W3C

XQuery 1.0: An XML Query Language

W3C Working Draft 02 May 2003

This version:
http://www.w3.org/TR/2003/WD-xquery-20030502/
Latest version:
http://www.w3.org/TR/xquery/
Previous versions:
http://www.w3.org/TR/2002/WD-xquery-20021115/ http://www.w3.org/TR/2002/WD-xquery-20020816/ http://www.w3.org/TR/2002/WD-xquery-20020430/ http://www.w3.org/TR/2001/WD-xquery-20011220/ http://www.w3.org/TR/2001/WD-xquery-20010607/
Editors:
Scott Boag (XSL WG), IBM Research <scott_boag@us.ibm.com>
Don Chamberlin (XML Query WG), IBM Almaden Research Center <chamberlin@almaden.ibm.com>
Mary F. Fernandez (XML Query WG), AT&T Labs <mff@research.att.com>
Daniela Florescu (XML Query WG), BEA Systems <danielaf@bea.com>
Jonathan Robie (XML Query WG), DataDirect Technologies <jonathan.robie@datadirect-technologies.com>
Jérôme Siméon (XML Query WG), Bell Labs, Lucent Technologies <simeon@research.bell-labs.com>

Abstract

XML is a versatile markup language, capable of labeling the information content of diverse data sources including structured and semi-structured documents, relational databases, and object repositories. A query language that uses the structure of XML intelligently can express queries across all these kinds of data, whether physically stored in XML or viewed as XML via middleware. This specification describes a query language called XQuery, which is designed to be broadly applicable across many types of XML data sources.

Status of this Document

This is a public W3C Working Draft for review by W3C Members and other interested parties. This section describes the status of this document at the time of its publication. It is a draft document and may be updated, replaced, or made obsolete by other documents at any time. It is inappropriate to use W3C Working Drafts as reference material or to cite them as other than "work in progress." A list of current public W3C technical reports can be found at http://www.w3.org/TR/.

Much of this document is the result of joint work by the XML Query and XSL Working Groups, which are jointly responsible for XPath 2.0, a language derived from both XPath 1.0 and XQuery. The XPath 2.0 and XQuery 1.0 Working Drafts are generated from a common source. These languages are closely related, sharing much of the same expression syntax and semantics, and much of the text found in the two Working Drafts is identical.

This version contains a new syntax for identifying types, and new features that allow path expressions to select element and attribute nodes based on their types as well as their names. It introduces the concept of a "module," and permits one module to import a function library defined in another module. It introduces changes to the semantics of element constructors, including automatic validation of the constructed element. It changes some of the details of the semantics of arithmetic and comparison operators, including making the value comparison operators transitive. It introduces a syntax by which an implementation can add its own extensions to XQuery. It includes some grammar changes, including changes in the comment delimiters and the syntax of the cast expression. A detailed list of changes can be found in G Revision Log.

This document is a work in progress. It contains many open issues, and should not be considered to be fully stable. Vendors who wish to create preview implementations based on this document do so at their own risk. While this document reflects the general consensus of the working groups, there are still controversial areas that may be subject to change.

Public comments on this document and its open issues are welcome, in particular comments on Issue 510. Comments should be sent to the W3C XPath/XQuery mailing list, public-qt-comments@w3.org (archived at http://lists.w3.org/Archives/Public/public-qt-comments/).

XQuery 1.0 has been defined jointly by the XML Query Working Group and the XSL Working Group (both part of the XML Activity).

Patent disclosures relevant to this specification may be found on the XML Query Working Group's patent disclosure page at http://www.w3.org/2002/08/xmlquery-IPR-statements and the XSL Working Group's patent disclosure page at http://www.w3.org/Style/XSL/Disclosures.

Table of Contents

1 Introduction
2 Basics
    2.1 Expression Context
        2.1.1 Static Context
        2.1.2 Evaluation Context
    2.2 Input Functions
    2.3 Expression Processing
        2.3.1 Document Order
        2.3.2 Typed Value and String Value
        2.3.3 Serialization of Query Results
    2.4 Types
        2.4.1 Predefined Types
        2.4.2 Type Checking
        2.4.3 SequenceType
            2.4.3.1 SequenceType Matching
        2.4.4 Type Conversions
            2.4.4.1 Atomization
            2.4.4.2 Effective Boolean Value
    2.5 Error Handling
        2.5.1 Kinds of Errors
        2.5.2 Handling Dynamic Errors
        2.5.3 Errors and Optimization
    2.6 Optional Features
        2.6.1 Basic XQuery
        2.6.2 Schema Import Feature
        2.6.3 Static Typing Feature
        2.6.4 Extensions
            2.6.4.1 Pragmas
            2.6.4.2 Must-Understand Extensions
            2.6.4.3 XQuery Flagger
3 Expressions
    3.1 Primary Expressions
        3.1.1 Literals
        3.1.2 Variables
        3.1.3 Parenthesized Expressions
        3.1.4 Function Calls
        3.1.5 XQuery Comments
    3.2 Path Expressions
        3.2.1 Steps
            3.2.1.1 Axes
            3.2.1.2 Node Tests
        3.2.2 Predicates
        3.2.3 Unabbreviated Syntax
        3.2.4 Abbreviated Syntax
    3.3 Sequence Expressions
        3.3.1 Constructing Sequences
        3.3.2 Combining Sequences
    3.4 Arithmetic Expressions
    3.5 Comparison Expressions
        3.5.1 Value Comparisons
        3.5.2 General Comparisons
        3.5.3 Node Comparisons
        3.5.4 Order Comparisons
    3.6 Logical Expressions
    3.7 Constructors
        3.7.1 Direct Element Constructors
            3.7.1.1 Attributes
            3.7.1.2 Namespaces
            3.7.1.3 Content
            3.7.1.4 Whitespace in Element Content
            3.7.1.5 Type of a Constructed Element
        3.7.2 Computed Constructors
            3.7.2.1 Computed Element Constructors
            3.7.2.2 Computed Attribute Constructors
            3.7.2.3 Document Node Constructors
            3.7.2.4 Text Node Constructors
        3.7.3 Other Constructors and Comments
    3.8 FLWOR Expressions
        3.8.1 For and Let Clauses
        3.8.2 Where Clause
        3.8.3 Order By and Return Clauses
        3.8.4 Example
    3.9 Unordered Expressions
    3.10 Conditional Expressions
    3.11 Quantified Expressions
    3.12 Expressions on SequenceTypes
        3.12.1 Instance Of
        3.12.2 Typeswitch
        3.12.3 Cast
        3.12.4 Castable
        3.12.5 Constructor Functions
        3.12.6 Treat
    3.13 Validate Expressions
4 Modules and Prologs
    4.1 Version Declaration
    4.2 Namespace Declarations
    4.3 Default Namespace Declarations
    4.4 Schema Imports
    4.5 Module Imports
    4.6 Variable Definitions
    4.7 Validation Declaration
    4.8 Xmlspace Declaration
    4.9 Default Collation
    4.10 Function Definitions

Appendices

A XQuery Grammar
    A.1 EBNF
        A.1.1 Parsing Notes
    A.2 Lexical structure
        A.2.1 Whitespace Rules
        A.2.2 Lexical Rules
    A.3 Reserved Function Names
    A.4 Precedence Order
B Type Promotion and Operator Mapping
    B.1 Type Promotion
    B.2 Operator Mapping
C References
    C.1 Normative References
    C.2 Non-normative References
    C.3 Background References
    C.4 Informative Material
D Glossary
E Example Applications (Non-Normative)
    E.1 Joins
    E.2 Grouping
    E.3 Queries on Sequence
    E.4 Recursive Transformations
F XPath 2.0 and XQuery 1.0 Issues (Non-Normative)
G Revision Log (Non-Normative)
    G.1 18 April 2003


1 Introduction

As increasing amounts of information are stored, exchanged, and presented using XML, the ability to intelligently query XML data sources becomes increasingly important. One of the great strengths of XML is its flexibility in representing many different kinds of information from diverse sources. To exploit this flexibility, an XML query language must provide features for retrieving and interpreting information from these diverse sources.

XQuery is designed to meet the requirements identified by the W3C XML Query Working Group [XML Query 1.0 Requirements] and the use cases in [XML Query Use Cases]. It is designed to be a language in which queries are concise and easily understood. It is also flexible enough to query a broad spectrum of XML information sources, including both databases and documents. The Query Working Group has identified a requirement for both a human-readable query syntax and an XML-based query syntax. XQuery is designed to meet the first of these requirements. XQuery is derived from an XML query language called Quilt [Quilt], which in turn borrowed features from several other languages, including XPath 1.0 [XPath 1.0], XQL [XQL], XML-QL [XML-QL], SQL [SQL], and OQL [ODMG].

XQuery Version 1.0 is an extension of XPath Version 2.0. Any expression that is syntactically valid and executes successfully in both XPath 2.0 and XQuery 1.0 will return the same result in both languages. Since these languages are so closely related, their grammars and language descriptions are generated from a common source to ensure consistency, and the editors of these specifications work together closely.

XQuery also depends on and is closely related to the following specifications:

This document specifies a grammar for XQuery, using the same Basic EBNF notation used in [XML], except that grammar symbols always have initial capital letters. Unless otherwise noted (see A.2 Lexical structure), whitespace is not significant in the grammar. Grammar productions are introduced together with the features that they describe, and a complete grammar is also presented in the appendix [A XQuery Grammar].

In the grammar productions in this document, nonterminal symbols are underlined and literal text is enclosed in double quotes. Certain productions (including the productions that define DecimalLiteral, DoubleLiteral, and StringLiteral) employ a regular-expression notation. The following example production describes the syntax of a function call:

[94]    FunctionCall    ::=    QName "(" (ExprSingle ("," ExprSingle)*)? ")"

The production should be read as follows: A function call consists of a QName followed by an open-parenthesis. The open-parenthesis is followed by an optional argument list. The argument list (if present) consists of one or more expressions, separated by commas. The optional argument list is followed by a close-parenthesis. The symbol ExprSingle denotes an expression that does not contain any top-level commas (since top-level commas in a function call are used to separate the function arguments).

Certain aspects of language processing are described in this specification as implementation-defined or implementation-dependent. These terms are defined as follows:

Editorial note  
A future version of this document will include links between terms (in bold font) and their definitions.


2 Basics

The basic building block of XQuery is the expression. The language provides several kinds of expressions which may be constructed from keywords, symbols, and operands. In general, the operands of an expression are other expressions. XQuery is a functional language which allows various kinds of expressions to be nested with full generality. (However, unlike a pure functional language, it does not allow variable substitutability if the variable definition contains construction of new nodes.) XQuery is also a strongly-typed language in which the operands of various expressions, operators, and functions must conform to the expected types.

Like XML, XQuery is a case-sensitive language. All keywords in XQuery use lower-case characters.

The value of an expression is always a sequence, which is an ordered collection of zero or more items. An item is either an atomic value or a node. An atomic value is a value in the value space of an XML Schema atomic type, as defined in [XML Schema] (that is, a simple type that is not a list type or a union type). A node conforms to one of the seven node kinds described in [XQuery 1.0 and XPath 2.0 Data Model]. Each node has a unique node identity. Some kinds of nodes have typed values, string values, and names, which can be extracted from the node. The typed value of a node is a sequence of zero or more atomic values. The string value of a node is a value of type xs:string. The name of a node is a value of type xs:QName.

A sequence containing exactly one item is called a singleton sequence. An item is identical to a singleton sequence containing that item. Sequences are never nested--for example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3). A sequence containing zero items is called an empty sequence.

In this document, the namespace prefixes xs: and xsi: are considered to be bound to the XML Schema namespaces http://www.w3.org/2001/XMLSchema and http://www.w3.org/2001/XMLSchema-instance, respectively (as described in [XML Schema]), and the prefix fn: is considered to be bound to the namespace of XPath/XQuery functions, http://www.w3.org/2003/05/xpath-functions (described in [XQuery 1.0 and XPath 2.0 Functions and Operators]). In some cases, where the meaning is clear and namespaces are not important to the discussion, built-in XML Schema typenames such as integer and string are used without a namespace prefix. Also, this document assumes that the default function namespace(see 4.2 Namespace Declarations) is set to the namespace of XPath/XQuery functions, so function names appearing without a namespace prefix can be assumed to be in this namespace.

2.1 Expression Context

The expression context for a given expression consists of all the information that can affect the result of the expression. This information is organized into two categories called the static context and the evaluation context.

2.1.1 Static Context

The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation. This information can be used to decide whether the expression contains a static error.

Many of the components of the static context can be assigned initial values by means of a Prolog (see 4 Modules and Prologs). Any component of the static context that is not assigned a default value in the XQuery specification, and is not assigned a value in the Prolog, may be assigned an implementation-defined initial value. If processing of an expression relies on some component of the static context that has not been assigned a value, a static error is raised.

Editorial note  
The impact on static context of queries that consist of multiple modules is under study by the Working Group.

Static context consists of the following components:

  • In-scope namespaces. This is a set of (prefix, URI) pairs. The in-scope namespaces are used for resolving prefixes used in QNames within the expression. The in-scope namespaces include the namespaces bound to the predefined namespace prefixes xml, xs, xsi, fn, and xdt (defined in 4.2 Namespace Declarations.)

  • Default element namespace. This is a namespace URI. This namespace is used for any unprefixed QName appearing in a position where an element or type name is expected.

  • Default function namespace. This is a namespace URI. This namespace URI is used for any unprefixed QName appearing as the function name in a function call.

  • In-scope schema definitions. This is a generic term for all the element, attribute, and type definitions that are in scope during processing of an expression. It includes the following three parts:

    • In-scope type definitions. The in-scope type definitions always include the built-in types of [XML Schema] and the predefined types in the namespace http://www.w3.org/2003/05/xpath-datatypes, which has the predefined namespace prefix xdt. Additional type definitions may be added to the in-scope type definitions by the external environment. If the Schema Import Feature is supported, in-scope type definitions also include all type definitions found in imported schemas.

      XML Schema distinguishes named types, which are given a QName by the schema designer, must be declared at the top level of a schema, and are uniquely identified by their QName, from anonymous types, which are not given a name by the schema designer, must be local, and are identified in an implementation-dependent way. Both named types and anonymous types can be present in the in-scope type definitions.

    • In-scope element declarations. Each element declaration is identified either by a QName (for a top-level element) or by an implementation-defined element identifier (for a local element). Element declarations may be provided by the language environment.If the Schema Import Feature is supported, in-scope element declarations include all element declarations found in imported schemas. An element declaration includes information about the substitution groups to which this element belongs.

    • In-scope attribute declarations. Each attribute declaration is identified either by a QName (for a top-level attribute) or by an implementation-defined attribute identifier (for a local attribute). Attribute declarations may be provided by the language environment. If the Schema Import Feature is supported, in-scope attribute declarations include all attribute declarations found in imported schemas.

  • In-scope variables. This is a set of (QName, type) pairs. It defines the set of variables that have been declared and are available for reference within the expression. The QName represents the name of the variable, and the type represents its static data type.

    The static types of in-scope variables may be declared in the Prolog, derived from static analysis of the expressions in which the variables are bound, or provided by the external environment.

  • In-scope functions. This part of the static context defines the set of functions that are available to be called from within an expression. Each function is uniquely identified by its QName and its arity (number of parameters). The static context maps the QName and arity into a function signature and a function definition. The function signature specifies the static types of the function parameters and the function result. For a user-defined function, the function definition is an XQuery expression. For an external function, the function definition is implementation-defined.

    For each atomic type in the in-scope type definitions, there is a constructor function in the in-scope functions. Constructor functions are discussed in 3.12.5 Constructor Functions.

  • In-scope collations. This is a set of (URI, collation) pairs. It defines the names of the collations that are available for use in function calls that take a collation name as an argument. A collation may be regarded as an object that supports two functions: a function that given a set of strings, returns a sequence containing those strings in sorted order; and a function that given two strings, returns true if they are considered equal, and false if not.

  • Default collation. This is a collation. This collation is used by string comparison functions when no explicit collation is specified.

  • Validation mode. One of strict, lax, or skip. This specifies the mode in which validation is performed by element constructors and by validate expressions. If no validation mode is specified in the Prolog, the default validation mode is lax.

  • Validation context. Either global or a path, starting with a top-level element name or type name in the in-scope schema definitions. Validation context determines the context in which top-level names are interpreted during validation of an element. The validation context for the outermost expression in a query is global. Validation context is affected by element constructors and by validate expressions.

  • XMLSpace policy. This policy, declared in the Prolog, controls the processing of whitespace by element constructors. Its value may be preserve or strip.

  • Base URI. This is an absolute URI, used when necessary in the resolution of relative URIs (for example, by the fn:resolve-uri function.) The base URI is always provided by the external environment.

XQuery Version 1.0 includes XPath Version 2.0 as a subset. In addition to the static context items listed above, XPath 2.0 requires a static context item named XPath 1.0 compatibility mode. Since XQuery does not support this mode, it always sets this context item to false when evaluating an XPath expression.

2.1.2 Evaluation Context

The evaluation context of an expression is defined as information that is available at the time the expression is evaluated.

One component of the evaluation context, the dynamic variables, can be set by the Prolog. Any component of the evaluation context that is not assigned a default value in the XQuery specification, and is not assigned a value in the Prolog, may be assigned an implementation-defined initial value. If processing of an expression relies on some component of the evaluation context that has not been assigned a value, a dynamic error is raised.

The evaluation context consists of all the components of the static context, and the additional components listed below.

The first three components of the evaluation context (context item, context position, and context size) are called the focus of the expression. The focus enables the processor to keep track of which nodes are being processed by the expression.

The focus for the outermost expression may supplied by the environment in which the expression is evaluated--otherwise, the focus for the outermost expression is undefined. Any reference to a component of an undefined focus raises an error. Certain language constructs, notably the path expression E1/E2 and the predicate expression E1[E2], create a new focus for the evaluation of a sub-expression. In these constructs, E2 is evaluated once for each item in the sequence that results from evaluating E1. Each time E2 is evaluated, it is evaluated with a different focus. The focus for evaluating E2 is referred to below as the inner focus, while the focus for evaluating E1 is referred to as the outer focus. The inner focus exists only while E2 is being evaluated. When this evaluation is complete, evaluation of the containing expression continues with its original focus unchanged.

  • The context item is the item currently being processed. An item is either an atomic value or a node. When the context item is a node, it can also be referred to as the context node. The context item is returned by the expression ".". When an expression E1/E2 or E1[E2] is evaluated, each item in the sequence obtained by evaluating E1 becomes the context item in the inner focus for an evaluation of E2.

  • The context position is the position of the context item within the sequence of items currently being processed. It changes whenever the context item changes. Its value is always an integer greater than zero. The context position is returned by the expression fn:position(). When an expression E1/E2 or E1[E2] is evaluated, the context position in the inner focus for an evaluation of E2 is the position of the context item in the sequence obtained by evaluating E1. The position of the first item in a sequence is always 1 (one). The context position is always less than or equal to the context size.

  • The context size is the number of items in the sequence of items currently being processed. Its value is always an integer greater than zero. The context size is returned by the expression last(). When an expression E1/E2 or E1[E2] is evaluated, the context size in the inner focus for an evaluation of E2 is the number of items in the sequence obtained by evaluating E1.

  • Dynamic variables. This is a set of (QName, value) pairs. It contains the same QNames as the in-scope variables in the static context for the expression. Each variable name is associated with a typed value. The dynamic type associated with the value of a variable may be more specific than the static type associated with the same variable. The value of a variable is, in general, a sequence.

    The typed value of a variable may be set by execution of an expression that binds a value to the variable, by the Prolog, or by the external environment.

  • Current date and time. This information represents an implementation-dependent point in time during processing of a query or transformation. It can be retrieved by the fn:current-date, fn:current-time, and fn:current-dateTime functions. If invoked multiple times during the execution of a query or transformation, these functions always returns the same result.

  • Implicit timezone. This is the timezone to be used when a date, time, or dateTime value that does not have a timezone is used in a comparison or in any other operation. This value is an instance of xdt:dayTimeDuration that is implementation-defined. See [ISO 8601] for the range of legal values of a timezone.

  • Input sequence. An input sequence is a sequence of nodes that can be accessed by the input function. It might be thought of as an "implicit input". The content of the input sequence is determined in an implementation-defined way.

2.2 Input Functions

XQuery has a set of functions that provide access to input data. These functions are of particular importance because they provide a way in which an expression can reference a document or a collection of documents. The input functions are described informally here, and in more detail in [XQuery 1.0 and XPath 2.0 Functions and Operators].

The input sequence is a part of the evaluation context for an expression. The way in which nodes are assigned to the input sequence is implementation-defined. For example, one implementation might provide a fixed mapping from a directory system to the input sequence, another implementation might provide a graphical user interface that allows users to choose a data source for the input sequence, and a third implementation might support UNIX-style pipes, allowing the output of one query to become the input sequence for another query.

The input functions supported by XQuery are as follows:

  • The fn:input function, which takes no parameters, returns the input sequence. For example, the expression fn:input()//customer returns all the customer elements that are descendants of nodes in the input sequence. If no input sequence has been bound, the fn:input function raises a dynamic error.

  • The fn:collection function returns the nodes found in a collection. A collection may be any sequence of nodes. A collection is identified by a string, which must be a valid URI. For example, the expression fn:collection("http://example.org")//customer identifies all the customer elements that are descendants of nodes found in the collection whose URI is http://example.org.

  • The fn:doc function, when its first argument is a string containing a single URI that refers to an XML document, returns a document node whose content is the Data Model representation of the given document.

If a given input function is invoked repeatedly with the same arguments during the scope of a single query or transformation, each invocation returns the same result.

2.3 Expression Processing

Editorial note  
Some material in this section duplicates material in [XQuery 1.0 and XPath 2.0 Data Model]. Work is in progress to decide where this material will be normatively defined (see Issue 554.)

XQuery is defined in terms of the [XQuery 1.0 and XPath 2.0 Data Model] (referred to in this document simply as the Data Model), which represents information in the form of nodes and atomic values. Before an XQuery expression can be processed, the input documents to be operated on by the expression must be represented in the Data Model. For example, an XML document might be converted to the Data Model by the following steps:

  1. The document might be parsed using an XML parser that generates an XML Information Set (see [XML Infoset]).

  2. The parsed document might be validated against one or more schemas. This process, which is described in [XML Schema], results in an abstract information structure called the Post-Schema Validation Infoset (PSVI).

  3. If necessary, the PSVI can be transformed to make it acceptable for processing by a particular system. For example, if the implementation understands only built-in XML Schema types, user-defined typenames in the PSVI might be replaced by their built-in base types or by generic types such as xs:anyType (for elements) and xs:anySimpleType (for attributes).

  4. The PSVI can be transformed into the Data Model by a process described in [XQuery 1.0 and XPath 2.0 Data Model]. During this transformation, an error is raised if the PSVI contains an element, attribute, or type whose expanded name matches a name in the in-scope schema definitions (ISSD), but whose definition in the PSVI is not consistent with the corresponding definition in the ISSD. Typenames in the PSVI that are not present in the ISSD are replaced by xs:anyType (for types of elements) or xs:anySimpleType (for types of attributes). At the conclusion of the transformation process, every element name, attribute name, and type name in the resulting Data Model instance matches an entry in the ISSD.

The above steps provide an example of how a Data Model instance might be constructed. A Data Model instance might also be synthesized directly from a relational database, or constructed in some other way. XQuery is defined in terms of operations on the Data Model, but it does not place any constraints on how the input Data Model instance is constructed (except for the constraint that the result must be consistent with the in-scope schema definitions).

Each element or attribute node in the Data Model has an annotation that indicates its dynamic type. If the Data Model was derived from an input XML document, the dynamic types of the elements and attributes are derived from schema validation. The dynamic type of an element or attribute indicates its range of values--for example, an attribute named version might have the dynamic type xs:decimal, indicating that it contains a decimal value.

The value of an attribute is represented directly within the attribute node. An attribute node whose type is unknown (such as might occur in a schemaless document) is annotated with the dynamic type xdt:untypedAtomic.

The value of an element is represented by the children of the element node, which may include text nodes and other element nodes. The dynamic type of an element node indicates how the values in its child text nodes are to be interpreted. An element whose type is unknown (such as might occur in a schemaless document) is annotated with the type xs:anyType.

Atomic values in the Data Model also carry dynamic type annotations. An atomic value of unknown type is annotated with the type xdt:untypedAtomic. Under certain circumstances (such as during processing of an arithmetic operator), an atomic value of xdt:untypedAtomic may be cast into a more specific type (such as xs:double).

This document provides a description of how each kind of expression is processed. For each expression, the operands and result are instances of the Data Model.

The terms document order, typed value, and string value are described here because they are of particular importance for the processing of expressions.

2.3.1 Document Order

Document order defines a total ordering among all the nodes seen by the language processor. Informally, document order corresponds to a pre-order, depth-first, left-to-right traversal of the nodes in the Data Model.

Within a given document, the document node is the first node, followed by element nodes, text nodes, comment nodes, and processing instruction nodes in the order of their representation in the XML form of the document (after expansion of entities). Element nodes occur before their children, and the children of an element node occur before its following siblings. The namespace nodes of an element immediately follow the element node, in implementation-defined order. The attribute nodes of an element immediately follow its namespace nodes, and are also in implementation-defined order.

The relative order of nodes in distinct documents is implementation-defined but stable within a given query or transformation. Given two distinct documents A and B, if a node in document A is before a node in document B, then every node in document A is before every node in document B. The relative order among free-floating nodes (those not in a document) is also implementation-defined but stable.

2.3.2 Typed Value and String Value

Nodes have a typed value and a string value that can be extracted by calling the fn:data function and the fn:string function, respectively. The typed value of a node is a sequence of atomic values, and the string value of a node is a string. Element and attribute nodes also have a type annotation, which is a type identifier that is found in the in-scope type definitions. The type annotation represents the dynamic (run-time) type of the node. XQuery does not provide a way to directly access the type annotation of an element or attribute node.

The typed value and string value for each kind of node are defined by the dm:typed-value and dm:string-value accessors in [XQuery 1.0 and XPath 2.0 Data Model]. The relationship between the typed value and the string value for various kinds of nodes is described and illustrated by examples below.

  1. For text, document, comment, processing instruction, and namespace nodes, the typed value of the node is the same as its string value, as an instance of xdt:untypedAtomic. (The string value of a document node is formed by concatenating the string values of all its descendant text nodes, in document order.)

  2. The typed value of an attribute node with the type annotation xdt:untypedAtomic is the same as its string value, as an instance of xdt:untypedAtomic. The typed value of an attribute node with any other type annotation is derived from its string value and type annotation in a way that is consistent with schema validation.

    Example: A1 is an attribute having string value "3.14E-2" and type annotation xs:double. The typed value of A1 is the xs:double value whose lexical representation is 3.14E-2.

    Example: A2 is an attribute with type annotation IDREFS, which is a list type derived from IDREF. Its string value is "bar baz faz". The typed value of A2 is a sequence of three atomic values ("bar", "baz", "faz"), each of type IDREF. The typed value of a node is never treated as an instance of a named list type. Instead, if the type annotation of a node is a list type (such as IDREFS), its typed value is treated as a sequence of the underlying base type (such as IDREF).

  3. For an element node, the relationship between typed value and string value depends on the node's type annotation, as follows:

    1. If the type annotation is xs:anyType, or denotes a complex type with mixed content, then the typed value of the node is equal to its string value, as an instance of xdt:untypedAtomic.

      Example: E1 is an element node having type annotation xs:anyType and string value "1999-05-31". The typed value of E1 is "1999-05-31", as an instance of xdt:untypedAtomic.

      Example: E2 is an element node with the type annotation formula, which is a complex type with mixed content. The content of E2 consists of the character "H", a child element named subscript with string value "2", and the character "O". The typed value of E2 is "H2O" as an instance of xdt:untypedAtomic.

    2. If the type annotation denotes a simple type or a complex type with simple content, then the typed value of the node is derived from its string value and its type annotation in a way that is consistent with schema validation.

      Example: E3 is an element node with the type annotation cost, which is a complex type that has several attributes and a simple content type of xs:decimal. The string value of E3 is "74.95". The typed value of E3 is 74.95, as an instance of xs:decimal.

      Example: E4 is an element node with the type annotation hatsizelist, which is a simple type derived by list from the type hatsize, which in turn is derived from xs:integer. The string value of E4 is "7 8 9". The typed value of E4 is a sequence of three values (7, 8, 9), each of type hatsize.

    3. If the type annotation denotes a complex type with empty content, then the typed value of the node is the empty sequence.

    4. If the type annotation denotes a complex type with non-mixed complex content, then the typed value of the node is undefined. The fn:data function raises an error when applied to such a node.

      Example: E5 is an element node with the type annotation weather, which is a complex type whose content type specifies elementOnly. E5 has two child elements named temperature and precipitation. The typed value of E5 is undefined, and the fn:data function applied to E5 raises an error.

2.3.3 Serialization of Query Results

Serialization is the process of converting an instance of the [XQuery 1.0 and XPath 2.0 Data Model] into a sequence of octets. The general framework for serialization of the Data Model is described in [XSLT 2.0 and XQuery 1.0 Serialization].

An XQuery implementation is not required to provide a serialization interface. For example, an implementation may only provide a DOM interface or an interface based on an event stream. In these cases, serialization would be done outside of the scope of this specification.

[XSLT 2.0 and XQuery 1.0 Serialization] defines a set of serialization parameters that govern the serialization process. If an XQuery implementation provides a serialization interface, it must support the "xml" value of the method parameter. In addition, the serialization interface may support (and may expose to users) any of the following serialization parameters (a default value is specified in each case):

  • encoding: default is implementation-defined.

  • cdata-section-elements: default is empty.

  • doctype-system: default is empty.

  • doctype-public: default is empty.

  • escape-uri-attributes: default is no.

  • indent: default is no.

  • media-type: default is implementation-defined.

  • normalize-unicode: default is implementation-defined.

  • omit-xml-declaration: default is yes.

  • standalone: default is yes.

  • character-map: default is empty.

  • version: default is 1.0.

2.4 Types

XQuery is a strongly typed language with a type system based on [XML Schema]. When the type of a value is incompatible with the expected type for the context in which it is used, a type error is raised. A type error may be detected and reported during the analysis phase or during the evaluation phase, as described in 2.4.2 Type Checking.

The XQuery type system is formally defined in [XQuery 1.0 Formal Semantics]. This section presents a summary of types from a user's perspective.

2.4.1 Predefined Types

All the built-in types of [XML Schema] are recognized by XQuery. These built-in types are in the namespace http://www.w3.org/2001/XMLSchema, which has the predefined namespace prefix xs. Some examples of built-in schema types include xs:integer, xs:string, and xs:date.

In addition, XQuery recognizes the predefined types listed below. All these predefined types are in the namespace http://www.w3.org/2003/05/xpath-datatypes, which has the predefined namespace prefix which is xdt.

  1. xdt:anyAtomicType is an abstract type that includes all atomic values (and no values that are not atomic). It is a subtype of xs:anySimpleType, which is the base type for all simple types, including atomic, list, and union types. All specific atomic types such as xs:integer, xs:string, and xdt:untypedAtomic, are subtypes of xdt:anyAtomicType.

  2. xdt:untypedAtomic is a specific atomic type used for untyped data, such as text that is not given a specific type by schema validation. It has no subtypes.

  3. xdt:dayTimeDuration is a subtype of xs:duration whose lexical representation contains only day, hour, minute, and second components.

  4. xdt:yearMonthDuration is a subtype of xs:duration whose lexical representation is restricted to contain only year and month components.

For more details about predefined types, see [XQuery 1.0 and XPath 2.0 Functions and Operators].

Additional types may be defined in schemas and imported into a query by means of a schema import, as discussed in 4.4 Schema Imports, or added to the in-scope type definitions by the external environment.

2.4.2 Type Checking

XQuery defines two phases of processing called the analysis phase and the evaluation phase.

The analysis phase depends on the expression itself and on the static context. The analysis phase does not depend on any input data. The purpose of type-checking during the analysis phase is to provide early detection of type errors and to compute the type of a result.

During the analysis phase, each expression is assigned a static type. In some cases, the static type is derived from the lexical form of the expression; for example, the static type of the literal 5 is xs:integer. In other cases, the static type of an expression is inferred according to rules based on the static types of its operands; for example, the static type of the expression 5 + 1.2 is xs:decimal. The static type of an expression may be either a named type or a structural description--for example, xs:boolean? denotes an optional occurrence of the xs:boolean type. The rules for inferring the static types of various expressions are described in [XQuery 1.0 Formal Semantics]. During the analysis phase, if static type checking is in effect and an operand of an expression is found to have a static type that is not appropriate for that operand, a type error is raised. If static type checking raises no errors and assigns a static type T to an expression, then execution of the expression on valid input data is guaranteed either to produce a value of type T or to raise a dynamic error.

The evaluation phase is performed only after successful completion of the analysis phase. The evaluation phase depends on input data, on the expression being evaluated, and on the evaluation context. During the evaluation phase, a dynamic type is associated with each value as it is computed. The dynamic type of a value may be either a structural type (such as "sequence of integers") or a named type. The dynamic type of a value may be more specific than the static type of the expression that computed it (for example, the static type of an expression might be "zero or more integers or strings," but at run time its value may have the dynamic type "integer.") If an operand of an expression is found to have a dynamic type that is incompatible with the expected type for that operand, a type error is raised.

Even though static typing can catch many type errors before an expression is executed, it is possible for an expression to raise an error during evaluation that was not detected by static analysis. For example, an expression may contain a cast of a string into an integer, which is statically valid. However, if the actual value of the string at run time cannot be cast into an integer, a dynamic error will result. Similarly, an expression may apply an arithmetic operator to a value whose static type is xs:anySimpleType. This is not a static error, but at run time, if the value cannot be successfully cast to a numeric type, a dynamic error will be raised.

It is also possible for static analysis of an expression to raise a type error, even though execution of the expression on certain inputs would be successful. For example, an expression might contain a function that requires an element as its parameter, and the analysis phase might infer the static type of the function parameter to be an optional element. This case would be treated as a static type error, even though the function call would be successful for input data in which the optional element is present.

2.4.3 SequenceType

When it is necessary to refer to a type in an XQuery expression, the syntax shown below is used. This syntax production is called "SequenceType", since it describes the type of an XQuery value, which is a sequence.

SequenceType
[117]    SequenceType    ::=    (ItemType OccurrenceIndicator?)
| "empty" "(" ")"
[133]    OccurrenceIndicator    ::=    "?" | "*" | "+"
[119]    ItemType    ::=    AtomicType | KindTest | "item" "(" ")"
[118]    AtomicType    ::=    QName
[120]    KindTest    ::=    DocumentTest
| ElementTest
| AttributeTest
| ProcessingInstructionTest
| CommentTest
| TextTest
| AnyKindTest
[123]    ProcessingInstructionTest    ::=    "processing-instruction" "(" StringLiteral? ")"
[125]    CommentTest    ::=    "comment" "(" ")"
[126]    TextTest    ::=    "text" "(" ")"
[127]    AnyKindTest    ::=    "node" "(" ")"
[124]    DocumentTest    ::=    "document-node" "(" ElementTest? ")"
[121]    ElementTest    ::=    "element" "(" ((SchemaContextPath LocalName)
| (NodeName ("," TypeName "nillable"?)?))? ")"
[122]    AttributeTest    ::=    "attribute" "(" ((SchemaContextPath "@" LocalName)
| ("@" NodeName ("," TypeName)?))? ")"
[128]    SchemaContextPath    ::=    SchemaGlobalContext "/" SchemaContextStep "/"*
[14]    SchemaGlobalContext    ::=    QName | SchemaGlobalTypeName
[15]    SchemaContextStep    ::=    QName
[13]    SchemaGlobalTypeName    ::=    "type" "(" QName ")"
[130]    LocalName    ::=    QName
[131]    NodeName    ::=    QName | "*"
[132]    TypeName    ::=    QName | "*"

QNames appearing in a SequenceType have their prefixes expanded to namespace URIs by means of the in-scope namespaces and the default element namespace. It is a static error to use a name in a SequenceType if that name is not found in the appropriate part of the in-scope schema definitions. If the name is used as an element name, it must appear in the in-scope element declarations; if it is used as an attribute name, it must appear in the in-scope attribute declarations; and if it is used as a type name, it must appear in the in-scope type definitions.

Here are some examples of SequenceTypes that might be used in XQuery expressions:

  • xs:date refers to the built-in Schema type date

  • attribute()? refers to an optional attribute

  • element() refers to any element

  • element(po:shipto, po:address) refers to an element that has the name po:shipto (or is in the substitution group of that element), and has the type annotation po:address (or a subtype of that type)

  • element(po:shipto, *) refers to an element named po:shipto (or in the substitution group of po:shipto), with no restrictions on its type

  • element(*, po:address) refers to an element of any name that has the type annotation po:address (or a subtype of po:address). If the keyword nillable were used following po:address, that would indicate that the element may have empty content and the attribute xsi:nil="true", even though the declaration of the type po:address has required content.

  • node()* refers to a sequence of zero or more nodes of any type

  • item()+ refers to a sequence of one or more nodes or atomic values

2.4.3.1 SequenceType Matching

During processing of an expression, it is sometimes necessary to determine whether a given value matches a type that was declared using the SequenceType syntax. This process is known as SequenceType matching. For example, an instance of expression returns true if a given value matches a given type, or false if it does not.

SequenceType matching between a given value and a given SequenceType is performed as follows:

If the SequenceType is empty(), the match succeeds only if the value is an empty sequence. If the SequenceType is an ItemType with no OccurrenceIndicator, the match succeeds only if the value contains precisely one item and that item matches the ItemType (see below). If the SequenceType contains an ItemType and an OccurrenceIndicator, the match succeeds only if the number of items in the value is consistent with the OccurrenceIndicator, and each of these items matches the ItemType. As a consequence of these rules, a value that is an empty sequence matches any SequenceType whose occurrence indicator is * or ?.

An OccurrenceIndicator indicates the number of items in a sequence, as follows:

  • ? indicates zero or one items

  • * indicates zero or more items

  • + indicates one or more items

As stated above, an item may be a node or an atomic value. The process of matching a given item against a given ItemType is performed as follows

  1. The ItemType item() matches any single item. For example, item() matches the atomic value 1 or the element <a/>.

  2. If an ItemType consists simply of a QName, that QName must be the name of an atomic type that is in the in-scope type definitions; otherwise a static error is raised. An ItemType consisting of the QName of an atomic type matches a value if the dynamic type of the value is the same as the named atomic type, or is derived from the named atomic type by restriction. For example, the ItemType xs:decimal matches the value 12.34 (a decimal literal); it also matches a value whose dynamic type is shoesize, if shoesize is an atomic type derived by restriction from xs:decimal. The named atomic type may be a generic type such as xdt:anyAtomicType. (Note that names of non-atomic types such as xs:IDREFS are not accepted in this context.)

  3. The following ItemTypes (referred to generically as KindTests) match nodes:

    1. node() matches any node.

    2. text() matches any text node.

    3. processing-instruction() matches any processing instruction node.

    4. processing-instruction(N ) matches any processing instruction node whose name (called its "PITarget" in XML) is equal to N, where N is a StringLiteral. Example: processing-instruction("browser") matches any processing instruction directed to the application named browser.

    5. comment() matches any comment node.

    6. document-node() matches any document node.

    7. document-node(E) matches any document node whose content consists of exactly one element node that matches E, where E is an ElementTest (see below). Example: document-node(element(book)) matches any document node whose content consists of exactly one element node named book, that conforms to the schema declaration for the top-level element book.

    8. An ElementTest (see below) matches an element node, optionally qualifying the node by its name, its type, or both.

    9. An AttributeTest (see below) matches an attribute node, optionally qualifying the node by its name, its type, or both.

An ElementTest is used to match an element node by its name and/or type. An ElementTest may take one of the following forms:

  1. element(), or element(*), or element(*,*). All these forms of ElementTest are equivalent, and they all match any single element node, regardless of its name or type.

  2. element(N, T), where N is a QName and T is a QName optionally followed by the keyword nillable. In this case, T must be the name of a top-level type definition in the in-scope type definitions. The ElementTest matches a given element node if:

    1. the name of the given element node is equal to N (expanded QNames match), or is equal to the name of any element in a substitution group headed by a top-level element with the name N; and:

    2. the type annotation of the given element node is T, or is a named type that is derived by restriction or extension from T. However, this test is not satisfied if the given element node has an attribute xsi:nil="true" and T does not specify nillable.

    The following examples illustrate this form of ElementTest, matching an element node whose name is person and whose type annotation is surgeon (the second example permits the element to have xsi:nil="true"):

    element(person, surgeon)
    element(person, surgeon nillable)
    
  3. element(N), where N is a QName. This form is very similar to the previous form, except that the required type, rather than being named explicitly, is taken from the top-level declaration of element N. In this case, N must be the name of a top-level element declaration in the in-scope element declarations. The ElementTest matches a given element node if:

    1. the name of the given element node is equal to N (expanded QNames match), or is equal to the name of any element in a substitution group headed by N; and:

    2. the type annotation of the given element node is the same as, or derived by restriction or extension from, the type of the top-level declaration for element N. The types to be compared may be either named types (identified by QNames) or anonymous types (identified in an implementation-dependent way). However, this test is not satisfied if the given element node has an attribute xsi:nil="true" and the top-level declaration for element N does not specify nillable.



    The following example illustrates this form of ElementTest, matching an element node whose name is person and whose type annotation conforms to the top-level person element declaration in the in-scope element declarations:

    element(person)
    
  4. element(N, *), where N is a QName. This ElementTest matches a given element node if the name of the node is equal to N (expanded QNames match), or is equal to the name of any element in a substitution group headed by a top-level element with the name N. The given element node may have any type annotation.

    The following example illustrates this form of ElementTest, matching any element node whose name is person or is in the person substitution group, regardless of its type annotation:

    element(person, *)
    
  5. element(*, T), where T is a QName optionally followed by the keyword nillable. In this case, T must be the name of a top-level type definition in the in-scope type definitions. The ElementTest matches a given element node if the node's type annotation is T, or is a named type that is derived by restriction or extension from T. However, this test is not satisfied if the given element node has an attribute xsi:nil="true" and T does not specify nillable.

    The following examples illustrate this form of ElementTest, matching any element node whose type annotation is surgeon, regardless of its name (the second example permits the element to have xsi:nil="true"):

    element(*, surgeon)
    element(*, surgeon nillable)
    
  6. element(P), where P is a valid schema context path beginning with a top-level element name or type name in the in-scope schema definitions and ending with an element name. This ElementTest matches a given element node if:

    1. the name of the given element node is equal to the last name in the path (expanded QNames match), and:

    2. the type annotation of the given element node is the same as the type of the element represented by the schema path P.

    The following examples illustrate this form of ElementTest, matching element nodes whose name is person. In the first example, the node must conform to the schema definition of a person element in a staff element in a hospital element. In the second example, the node must conform to the schema definition of a person element within the top-level type schedule:

    element(hospital/staff/person)
    element(type(schedule)/person)
    

An AttributeTest is used to match an attribute node by its name and/or type. An AttributeTest may take one of the following forms:

  1. attribute(), or attribute(@*), or attribute(@*,*). All these forms of AttributeTest are equivalent, and they all match any single attribute node, regardless of its name or type.

  2. attribute(@N, T), where N and T are QNames. In this case, T must be the name of a top-level simple type definition in the in-scope type definitions. This AttributeTest matches a given attribute node if:

    1. the name of the given attribute node is equal to N (expanded QNames match), and:

    2. the type annotation of the given attribute node is T, or is a named type that is derived by restriction from T.

    The following example illustrates this form of AttributeTest, matching an attribute node whose name is price and whose type annotation is currency:

    attribute(@price, currency)
    
  3. attribute(@N), where N is a QName. This form is very similar to the previous form, except that the required type, rather than being named explicitly, is taken from the top-level attribute declaration with name N.In this case, N must be the name of a top-level attribute declaration in the in-scope attribute declarations. This AttributeTest matches a given attribute node if:

    1. the name of the given attribute node is equal to N (expanded QNames match), and:

    2. the type annotation of the given attribute node is the same as, or derived by restriction from, the type of the top-level attribute declaration for N. The types to be compared may be either named types (identified by QNames) or anonymous types (identified in an implementation-dependent way).



    The following example illustrates this form of AttributeTest, matching an attribute node whose name is price and whose type annotation conforms to the schema declaration for a top-level price attribute:

    attribute(@price)
    
  4. attribute(@N, *), where N is a QName. This AttributeTest matches a given attribute node if the name of the node is equal to N (expanded QNames match). The given attribute node may have any type annotation.

    The following example illustrates this form of AttributeTest, matching any attribute node whose name is price, regardless of its type annotation:

    attribute(@price, *)
    
  5. attribute(@*, T), where T is a QName. In this case, T must be the name of a top-level simple type definition in the in-scope type definitions. This AttributeTest matches a given attribute node if the node's type annotation is T, or is a named type that is derived by restriction from T.

    The following example illustrates this form of AttributeTest, matching any attribute node whose type annotation is currency, regardless of its name:

    attribute(@*, currency)
    
  6. attribute(P), where P is a valid schema context path beginning with a top-level element name or type name in the in-scope schema definitions, and ending with an attribute name (preceded by @). This AttributeTest matches a given attribute node if:

    1. the name of the given attribute node is equal to the last name in the path (expanded QNames match), and:

    2. the type annotation of the given attribute node is the same as the type of the attribute represented by the schema path P.

    The following examples illustrate this form of AttributeTest, matching attribute nodes whose name is price. In the first example, the node must conform to the schema definition of a price attribute in a product element in a catalog element. In the second example, the node must conform to the schema definition of a price attribute within the top-level type plan:

    attribute(catalog/product/@price)
    attribute(type(plan)/@price)
    

2.4.4 Type Conversions

Some expressions do not require their operands to exactly match the expected type. For example, function parameters and returns expect a value of a particular type, but automatically perform certain type conversions, such as extraction of atomic values from nodes, promotion of numeric values, and implicit casting of untyped values. The conversion rules for function parameters and returns are discussed in 3.1.4 Function Calls. Other operators that provide special conversion rules include arithmetic operators, which are discussed in 3.4 Arithmetic Expressions, and value comparisons, which are discussed in 3.5.1 Value Comparisons.

2.4.4.1 Atomization

Type conversions sometimes depend on a process called atomization, which is used when a sequence of atomic values is required. The result of atomization is either a sequence of atomic values or a type error. Atomization of a sequence is defined as the result of invoking the fn:data function on the sequence, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].

The semantics of fn:data are repeated here for convenience. The result of fn:data is the sequence of atomic values produced by applying the following rules to each item in the input sequence:

  • If the item is an atomic value, it is returned.

  • If the item is a node, it is replaced by its typed value.

Atomization may be used in processing the following types of expressions:

  • Arithmetic expressions

  • Comparison expressions

  • Function calls and returns

  • Cast expressions

2.4.4.2 Effective Boolean Value

Under certain circumstances (listed below), it is necessary to find the effective boolean value of a sequence. This is defined as the result of invoking the fn:boolean function on the sequence, as defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].

The semantics of fn:boolean are repeated here for convenience. fn:boolean returns false if its operand is any of the following:

  • An empty sequence.

  • The boolean value false.

  • A zero-length string ("").

  • A numeric value that is equal to zero.

  • The double or float value NaN.

Otherwise, fn:boolean returns true.

The effective boolean value of a sequence is computed implicitly during processing of the following types of expressions:

  • Logical expressions (and, or)

  • The fn:not function

  • The where clause of a FLWOR expression

  • Certain types of predicates, such as a[b].

  • Conditional expressions (if)

  • Quantified expressions (some, every)

Note that the definition of effective boolean value is not used when casting a value to the type xs:boolean.

2.5 Error Handling

2.5.1 Kinds of Errors

As described in 2.4.2 Type Checking, XQuery defines an analysis phase, which does not depend on input data, and an evaluation phase, which does depend on input data.

The result of the analysis phase is either success or one or more type errors and/or static errors. Type errors reported by the analysis phase occur when the static type of an expression is not correct for the context in which it appears. Static errors are non-type-related errors such as syntax errors. The means by which errors are reported during the analysis phase is implementation-defined.

The result of the evaluation phase is either a result value, a type error, or a dynamic error. Type errors are raised during the evaluation phase when the dynamic type of an expression is not correct for the context in which it appears. Dynamic errors are non-type-related errors such as numeric overflow. If evaluation of an expression yields a value (that is, it does not raise an error), the value must be the value specified by the dynamic semantics defined in [XQuery 1.0 Formal Semantics].

If an implementation can determine by static analysis that an expression will necessarily raise a dynamic error (for example, because it attempts to construct a decimal value from a constant string that is not in the lexical space of xs:decimal), the implementation is allowed to report this error during the analysis phase (as well as during the evaluation phase).

[XQuery 1.0 Formal Semantics] defines the set of static, dynamic, and type errors. In addition to these errors, an XQuery implementation may raise implementation-defined warnings, either during the analysis phase or the evaluation phase. The circumstances in which warnings are raised, and the ways in which warnings are handled, are implementation-defined.

In addition to the errors defined in this specification, an implementation may raise a dynamic error if insufficient resources are available for processing a given expression. For example, an implementation may specify limitations on the maximum numbers or sizes of various objects. These limitations, and the consequences of exceeding them, are implementation-defined.

2.5.2 Handling Dynamic Errors

Except as noted in this document, if any operand of an expression raises a dynamic error, the expression also raises a dynamic error. If an expression can validly return a value or raise a dynamic error, the implementation may choose to return the value or raise the dynamic error. For example, the logical expression expr1 and expr2 may return the value false if either operand returns false, or may raise a dynamic error if either operand raises a dynamic error.

If more than one operand of an expression raises an error, the implementation may choose which error is raised by the expression. For example, in this expression:

($x div $y) + xs:decimal($z)

both ($x div $y) and xs:decimal($z) may raise an error. The implementation may choose which error is raised by the "+" expression. Once one operand raises an error, the implementation is not required, but is permitted, to evaluate any other operands.

A dynamic error carries an error value, which may be a single item or an empty sequence. For example, an error value might be an integer, a string, a QName, or an element. An implementation may provide a mechanism whereby an application-defined error handler can process error values and produce diagnostics; in the absence of such an error handler, the string-value of the error value may be used directly as an error message.

A dynamic error may be raised by a built-in function or operator. For example, the input function raises an error if the input sequence is not defined in the evaluation context.

An error can be raised explicitly by calling the fn:error function, which only raises an error and never returns a value. The fn:error function takes an optional item as its parameter, which is used as the error value. For example, the following function call raises a dynamic error whose error value is a string:

fn:error(fn:concat("Unexpected value ", fn:string($v)))

2.5.3 Errors and Optimization

Because different implementations may choose to evaluate or optimize an expression in different ways, the detection and reporting of dynamic errors is implementation dependent.

When an implementation is able to evaluate an expression without evaluating some subexpression, the implementation is never required to evaluate that subexpression solely to determine whether it raises a dynamic error. For example, if a function parameter is never used in the body of the function, an implementation may choose whether to evaluate the expression bound to that parameter in a function call.

In some cases, an optimizer may be able to achieve substantial performance improvements by rearranging an expression so that the underlying operations such as projection, restriction, and sorting are performed in a different order than that specified in [XQuery 1.0 Formal Semantics]. In such cases, dynamic errors may occur that could not have occurred if the expression were evaluated as written. For example, consider the following expression:

$N[@x castable as xs:date]
      [xs:date(@x) gt xs:date("2000-01-01")]

This expression cannot fail with a casting error if it is evaluated exactly as written. An implementation is permitted, however, to reorder the predicates to achieve better performance (for example, by taking advantage of an index). This reordering could cause the above expression to fail. However, an expression must not be rearranged in a way that causes it to return a non-error result that is different from the result defined by [XQuery 1.0 Formal Semantics].

To avoid unexpected errors caused by reordering of expressions, tests that are designed to prevent dynamic errors should be expressed using conditional expressions, as in the following example:

$N[if (@x castable as xs:date)
   then xs:date(@x) gt xs:date("2000-01-01")
   else false()]

In the case of a conditional expression, the implementation is required not to evaluate the then branch if the condition is false, and not to evaluate the else branch if the condition is true. Conditional and typeswitch expressions are the only kinds of expressions that provide guaranteed conditions under which a particular subexpression will not be evaluated.

2.6 Optional Features

XQuery defines a a required level of functionality, called Basic XQuery, and two optional features called the Schema Import Feature and the Static Typing Feature.

2.6.1 Basic XQuery

A Basic XQuery implementation must implement the full XQuery language as described in this specification, subject to the following limitations:

  1. If a Prolog contains a Schema Import, a Basic XQuery implementation raises a static error.

  2. In a Basic XQuery implementation, the in-scope type definitions consist only of the built-in types defined in [XML Schema] and the additional predefined types in the http://www.w3.org/2003/05/xpath-datatypes namespace.

  3. A mapping from a Post-Schema Validation Infoset (PSVI) to the Data Model is specified in [XQuery 1.0 and XPath 2.0 Data Model]. In a Basic XQuery implementation, this mapping maps each datatype that is not one of the predefined types listed above into its nearest supertype that belongs to this list. As a result of this mapping, all complex types are mapped into xs:anyType. (Of course, mapping from a PSVI is only one way in which a Data Model instance might be constructed--other ways are also possible.)

  4. If any SequenceType contains a typename that is not one of the predefined types listed above, a Basic XQuery implementation raises a static error.

  5. If any SequenceType contains an ElementTest or AttributeTest that contains a TypeName or a SchemaContextPath, a Basic XQuery implementation raises a static error.

  6. If the processing of an expression depends on the type of some value, and that type is not one of the predefined types listed above, a Basic XQuery implementation raises a dynamic error.

  7. A Basic XQuery implementation is not required to raise type errors during the analysis phase. If an expression contains one or more non-type-related static errors, then a Basic XQuery implementation must raise at least one of these static errors during the analysis phase. If the analysis phase is successful but one or more dynamic errors are encountered during the evaluation phase, then a Basic XQuery implementation must raise at least one of these dynamic errors.

2.6.2 Schema Import Feature

The Schema Import Feature removes the limitations specified by Rules 1 through 6 of Basic XQuery.

During the analysis phase, in-scope schema definitions are derived from schemas named in Schema Import clauses in the Prolog. If more than one schema is imported, the definitions contained in these schemas are collected into a single pool of definitions. This pool of definitions must satisfy the conditions for schema validity set out in Sections 3 and 5 of [XML Schema] Part 1. In brief, the definitions must be valid, they must be complete and they must be unique--that is, the pool of definitions must not contain two or more schema components with the same name and target namespace. If any of these conditions is violated, a static error must be raised.

2.6.3 Static Typing Feature

The Static Typing Feature removes the limitation specified by Rule 7 of Basic XQuery. An implementation that includes this feature is required to detect type errors during the analysis phase. If an expression contains one or more static errors or type errors, then a Static Typing implementation must raise at least one of these errors during the analysis phase.

2.6.4 Extensions

An XQuery implementation may make two kinds of extensions to this specification, called pragmas and must-understand extensions. While an XQuery implementation may support either of these kinds of extensions, this does not negate the requirement to support the XQuery functionality defined in this specification.

2.6.4.1 Pragmas

A pragma may be used to provide additional information to an XQuery implementation.

[1]    Pragma    ::=    "(::" "pragma" QName PragmaContents* "::)" /* pn: parens */
[5]    PragmaContents    ::=    Char

The QName is any QName that contains an explicit namespace prefix. PragmaContents may consist of any sequence of characters that does not include the sequence "::)". Pragmas may be used anywhere that ignorable whitespace is allowed, and within element content. See A.2 Lexical structure for the exact lexical states where pragmas are recognized. A pragma is identified by its PragmaQName.

If an implementation does not support a pragma, then that pragma shall be ignored. If an implementation does support a pragma and the implementation determines that the PragmaContents are invalid, then a static error is raised. Otherwise, the effect of the pragma on the result of the Query is implementation-defined.

The following example shows how a pragma might be used:

declare namespace exq = "http://example.org/XQueryImplementation"
   (:: pragma exq:timeout 1000 ::)
   count(input()//author)

An implementation that supports the exq:timeout pragma might raise a dynamic error if it is unable to count the authors within 1000 seconds. An implementation that does not support this pragma would execute as long as necessary to count the authors.

2.6.4.2 Must-Understand Extensions

An implementation may extend XQuery functionality by supporting must-understand extensions.

[2]    MustUnderstandExtension    ::=    "(::" "extension" QName ExtensionContents* "::)" /* pn: parens */
[6]    ExtensionContents    ::=    Char

The QName is any QName that contains an explicit namespace prefix. ExtensionContents may consist of any sequence of characters that does not include the sequence "::)". A must-understand extension may be used anywhere that ignorable whitespace is allowed, and within element content. See A.2 Lexical structure for the exact lexical states where these extensions are recognized. A must-understand extension is identified by its ExtensionQName.

If an implementation does not support a must-understand extension, then a static error is raised. If an implementation does support a must-understand extension and the implementation determines that the ExtensionContents are invalid, then a static error is raised. Otherwise, the effect of the must-understand extension on the result of the Query is implementation-defined.

The following example shows how a must-understand extension might be used:

   declare namespace exq = "http://example.org/XQueryImplementation"

   for $e in doc("employees.xml")//employee
   order by $e/lastname (:: extension exq:RightToLeft ::)
   return $e

An implementation that supports the exq:RightToLeft extension might order the last names by examining characters from right to left instead of from left to right. An implementation that does not support this extension would raise a static error.

2.6.4.3 XQuery Flagger

An XQuery Flagger is a facility that is provided by an implementation that is able to identify queries that contain must-understand extensions. If an implementation supports must-understand extensions, then an XQuery Flagger must be provided. The XQuery Flagger is disabled by default; the mechanism by which the XQuery Flagger is enabled is implementation-defined. When enabled, the XQuery Flagger must raise a static error for an otherwise valid Query that contains a must-understand extension.

An XQuery Flagger is provided to assist programmers in producing queries that are portable among multiple conforming XQuery implementations.

The following example illustrates how an XQuery Flagger might be used:

xquery RightToLeft.xquery -Flagger=on

If RightToLeft.xquery contains a must-understand extension such as exq:RightToLeft, then this XQuery invocation will result in a static error. If the XQuery Flagger was not enabled and the implementation supports exq:RightToLeft, then this query might execute without error.

3 Expressions

This section introduces each of the basic kinds of expression. Each kind of expression has a name such as PathExpr, which is introduced on the left side of the grammar production that defines the expression. Since XQuery is a composable language, each kind of expression is defined in terms of other expressions whose operators have a higher precedence. In this way, the precedence of operators is represented explicitly in the grammar.

The order in which expressions are discussed in this document does not reflect the order of operator precedence. In general, this document introduces the simplest kinds of expressions first, followed by more complex expressions. For a complete overview of the grammar, see the Appendix [A XQuery Grammar].

[39]    Expr    ::=    ExprSingle ("," ExprSingle)*
[40]    ExprSingle    ::=    FLWORExpr
| QuantifiedExpr
| TypeswitchExpr
| IfExpr
| OrExpr

A query may consist of one or more modules, as described in 4 Modules and Prologs. If a query is executable, one of its modules has a Query Body containing an expression whose value is the result of the query. An expression is represented in the XQuery grammar by the symbol Expr.

The XQuery operator that has lowest precedence is the comma operator, which is used to concatenate two operands to form a sequence. As shown in the grammar, a general expression (Expr) can consist of two operands (ExprSingle) separated by a comma. The name ExprSingle denotes an expression that does not contain a top-level comma operator (despite its name, an ExprSingle may evaluate to a sequence containing more than one item.)

The symbol ExprSingle is used in various places in the grammar where an expression is not allowed to contain a top-level comma. For example, each of the arguments of a function call must be an ExprSingle, because commas are used to separate the arguments of a function call.

After the comma, the expressions that have next lowest precedence are FLWORExpr, QuantifiedExpr, TypeswitchExpr, IfExpr, and OrExpr. Each of these expressions is described in a separate section of this document.

3.1 Primary Expressions

Primary expressions are the basic primitives of the language. They include literals, variables, function calls, constructors, and the use of parentheses to control precedence of operators. Constructors are described in 3.7 Constructors.

[73]    PrimaryExpr    ::=    Literal | FunctionCall | ("$" VarName) | ParenthesizedExpr | Constructor
[20]    VarName    ::=    QName

3.1.1 Literals

A literal is a direct syntactic representation of an atomic value. XQuery supports two kinds of literals: numeric literals and string literals.

[91]    Literal    ::=    NumericLiteral | StringLiteral
[92]    NumericLiteral    ::=    IntegerLiteral | DecimalLiteral | DoubleLiteral
[7]    IntegerLiteral    ::=    Digits
[8]    DecimalLiteral    ::=    ("." Digits) | (Digits "." [0-9]*) /* ws: explicit */
[9]    DoubleLiteral    ::=    (("." Digits) | (Digits ("." [0-9]*)?)) ("e" | "E") ("+" | "-")? Digits /* ws: explicit */
[10]    StringLiteral    ::=    ('"' (PredefinedEntityRef | CharRef | ('"' '"') | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | ("'" "'") | [^'&])* "'") /* ws: significant */
[22]    PredefinedEntityRef    ::=    "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";" /* ws: explicit */
[24]    CharRef    ::=    "&#" (Digits | ("x" HexDigits)) ";" /* ws: explicit */

The value of a numeric literal containing no "." and no e or E character is an atomic value whose type is xs:integer and whose value is obtained by parsing the numeric literal according to the rules of the xs:integer datatype. The value of a numeric literal containing "." but no e or E character is an atomic value whose type is xs:decimal and whose value is obtained by parsing the numeric literal according to the rules of the xs:decimal datatype. The value of a numeric literal containing an e or E character is an atomic value whose type is xs:double and whose value is obtained by parsing the numeric literal according to the rules of the xs:double datatype.

The value of a string literal is an atomic value whose type is xs:string and whose value is the string denoted by the characters between the delimiting apostrophes or quotation marks. If the literal is delimited by apostrophes, two adjacent apostrophes within the literal are interpreted as a single apostrophe. Similarly, if the literal is delimited by quotation marks, two adjacent quotation marks within the literal are interpreted as one quotation mark.

If a string literal is used in an XQuery expression contained within the value of an XML attribute, the characters used to delimit the literal should be different from the characters that are used to delimit the attribute.(See 3.7.1.1 Attributes for examples of expressions used in attribute values.)

A string literal may contain a predefined entity reference, which is a short sequence of characters, beginning with an ampersand, that represents a single character that might otherwise have syntactic significance. Each predefined entity reference is replaced by the character it represents when the string literal is processed. The predefined entity references recognized by XQuery are as follows:

Entity Reference Character Represented
&lt; <
&gt; >
&amp; &
&quot; "
&apos; '

A string literal may also contain a character reference, which is an XML-style reference to a Unicode character, identified by its decimal or hexadecimal code point. For example, the Euro symbol (€) can be represented by the character reference &#8364;.

Here are some examples of literal expressions:

  • "12.5" denotes the string containing the characters '1', '2', '.', and '5'.

  • 12 denotes the integer value twelve.

  • 12.5 denotes the decimal value twelve and one half.

  • 125E2 denotes the double value twelve thousand, five hundred.

  • "He said, ""I don't like it.""" denotes a string containing two quotation marks and one apostrophe.

  • Ben &amp; Jerry&apos;s denotes the string "Ben & Jerry's".

  • &#8364;99.50 denotes the string "€99.50".

The boolean values true and false can be represented by calls to the built-in functions fn:true() and fn:false(), respectively.

Values of other XML Schema built-in types can be constructed by calling the constructor for the given type. The constructors for XML Schema built-in types are defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. In general, the name of a constructor function for a given type is the same as the name of the type (including its namespace). For example:

  • xs:integer("12") returns the integer value twelve.

  • xs:date("2001-08-25") returns an item whose type is xs:date and whose value represents the date 25th August 2001.

  • xdt:dayTimeDuration("PT5H") returns an item whose type is xdt:dayTimeDuration and whose value represents a duration of five hours.

It is also possible to construct values of various types by using a cast expression. For example:

  • 9 cast as hatsize returns the atomic value 9 whose type is hatsize.

3.1.2 Variables

A variable reference is a QName preceded by a $-sign. Two variable references are equivalent if their local names are the same and their namespace prefixes are bound to the same namespace URI in the in-scope namespaces. An unprefixed variable reference is in no namespace.

Every variable reference must match a name in the in-scope variables, which include variables from the following sources:

  1. A variable may be declared in a Prolog, in the current module or an imported module. See 4 Modules and Prologs for a discussion of modules and Prologs.

  2. A variable may be added to the in-scope variables by the host language environment.

  3. A variable may be bound by an XQuery expression. The kinds of expressions that can bind variables are FLWOR expressions (3.8 FLWOR Expressions), quantified expressions (3.11 Quantified Expressions), and typeswitch expressions (3.12.2 Typeswitch). Function calls also bind values to the formal parameters of functions before executing the function body.



Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a static error to reference a variable that is not in scope. If a variable is bound in the static context for an expression, that variable is in scope for the entire expression.

If a variable reference matches two or more bindings that are in scope, then the reference is taken as referring to the inner binding, that is, the one whose scope is smaller. At evaluation time, the value of a variable reference is the value of the expression to which the relevant variable is bound. The scope of a variable binding is defined separately for each kind of expression that can bind variables.

3.1.3 Parenthesized Expressions

[93]    ParenthesizedExpr    ::=    "(" Expr? ")"

Parentheses may be used to enforce a particular evaluation order in expressions that contain multiple operators. For example, the expression (2 + 4) * 5 evaluates to thirty, since the parenthesized expression (2 + 4) is evaluated first and its result is multiplied by five. Without parentheses, the expression 2 + 4 * 5 evaluates to twenty-two, because the multiplication operator has higher precedence than the addition operator.

Empty parentheses are used to denote an empty sequence, as described in 3.3.1 Constructing Sequences.

3.1.4 Function Calls

A function call consists of a QName followed by a parenthesized list of zero or more expressions, called arguments. If the QName in the function call has no namespace prefix, it is considered to be in the default function namespace.

If the expanded QName and number of arguments in a function call do not match the name and arity of an in-scope function in the static context, a static error is raised.

[94]    FunctionCall    ::=    QName "(" (ExprSingle ("," ExprSingle)*)? ")"

A function call is evaluated as follows:

  1. Each argument expression is evaluated, producing an argument value. The order of argument evaluation is implementation-dependent and a function need not evaluate an argument if the function can evaluate its body without evaluating that argument.

  2. Each argument value is converted by applying the function conversion rules listed below.

  3. If the function is a built-in function, it is executed using the converted argument values. The result is a value of the function's declared return type.

  4. If the function is a user-defined function, the converted argument values are bound to the formal parameters of the function, and the function body is evaluated. The value returned by the function body is then converted to the declared return type of the function by applying the function conversion rules.

    When a converted argument value is bound to a function parameter, the argument value retains its most specific dynamic type, even though this may be a subtype of the type of the formal parameter. For example, a function with a parameter $p of type xs:decimal can be invoked with an argument of type xs:integer, which is derived from xs:decimal. During the processing of this function invocation, the dynamic type of $p inside the body of the function is considered to be xs:integer. Similarly, the value returned by a function retains its most specific type, which may be a subtype of the declared return type of the function. For example, a function that has a declared return type of xs:decimal may in fact return a value of dynamic type xs:integer.

    A function does not inherit a focus (context item, context position, and context size) from the environment of the function call. During evaluation of a function body, the focus is undefined, except where it is defined by the action of some expression inside the function body. Use of an expression that depends on the focus when the focus is undefined raises a static error.

The function conversion rules are used to convert an argument value or a return value to its expected type; that is, to the declared type of the function parameteror return. The expected type is expressed as a SequenceType. The function conversion rules are applied to a given value as follows:

  • If the expected type is a sequence of an atomic type (possibly with an occurrence indicator *, +, or ?), the following conversions are applied:

    1. Atomization is applied to the given value, resulting in a sequence of atomic values.

    2. Each item in the atomic sequence that is of type xdt:untypedAtomic is cast to the expected atomic type.

    3. For each numeric item in the atomic sequence that can be promoted to the expected atomic type using the promotion rules in B.1 Type Promotion, the promotion is done.

  • If, after the above conversions, the resulting value does not match the expected type according to the rules for SequenceType Matching, a type error is raised. Note that the rules for SequenceType Matching permit a value of a derived type to be substituted for a value of its base type.

A core library of functions is defined in [XQuery 1.0 and XPath 2.0 Functions and Operators]. Additional functions may be declared in a Prolog, imported from a library module, or provided by the external environment as part of the static context. For details on processing function names that have no namespace prefix, see 4.2 Namespace Declarations.

Since the arguments of a function call are separated by commas, any argument expression that contains a top-level comma operator must be enclosed in parentheses. Here are some illustrative examples of function calls:

  • three-argument-function(1, 2, 3) denotes a function call with three arguments.

  • two-argument-function((1, 2), 3) denotes a function call with two arguments, the first of which is a sequence of two values.

  • two-argument-function(1, ()) denotes a function call with two arguments, the second of which is an empty sequence.

  • one-argument-function((1, 2, 3)) denotes a function call with one argument that is a sequence of three values.

  • one-argument-function(( )) denotes a function call with one argument that is an empty sequence.

  • zero-argument-function( ) denotes a function call with zero arguments.

3.1.5 XQuery Comments

[3]    ExprComment    ::=    "(:" (ExprCommentContent | ExprComment)* ":)" /* pn: parens */
[4]    ExprCommentContent    ::=    Char

XQuery comments can be used to provide informative annotation. These comments are lexical constructs only, and do not affect the processing of an expression. Comments are delimited by the symbols (: and :). Comments may be nested.

Comments may be used anywhere that ignorable whitespace is allowed, and within element content. See A.2 Lexical structure for the exact lexical states where comments are recognized.

The following is an example of a comment:

(: Houston, we have a problem :)

3.2 Path Expressions

A path expression can be used to locate nodes within a tree.

[68]    PathExpr    ::=    ("/" RelativePathExpr?)
| ("//" RelativePathExpr)
| RelativePathExpr
[69]    RelativePathExpr    ::=    StepExpr (("/" | "//") StepExpr)*

A path expression consists of a series of one or more steps, separated by "/" or "//", and optionally beginning with "/" or "//". An initial "/" or "//" is an abbreviation for one or more initial steps that are implicitly added to the beginning of the path expression, as described below.

A path expression consisting of a single step is evaluated as described in 3.2.1 Steps.

Each occurrence of // in a path expression is expanded as described in 3.2.4 Abbreviated Syntax, leaving a sequence of steps separated by /. This sequence of steps is then evaluated from left to right. Each operation E1/E2 is evaluated as follows: Expression E1 is evaluated, and if the result is not a sequence of nodes, a dynamic error is raised. Each node resulting from the evaluation of E1 then serves in turn to provide an inner focus for an evaluation of E2, as described in 2.1.2 Evaluation Context. Each evaluation of E2 must result in a sequence of nodes; otherwise, a dynamic error is raised. The sequences of nodes resulting from all the evaluations of E2 are merged, eliminating duplicate nodes based on node identity and sorting the results in document order.

As an example of a path expression, child::div1/child::para selects the para element children of the div1 element children of the context node, or, in other words, the para element grandchildren of the context node that have div1 parents.

A "/" at the beginning of a path expression is an abbreviation for the initial step fn:root(self::node()). The effect of this initial step is to begin the path at the root node of the tree that contains the context node. If the context item is not a node, a type error is raised.

A "//" at the beginning of a path expression is an abbreviation for the initial steps fn:root(self::node())/descendant-or-self::node(). The effect of these initial steps is to establish an initial node sequence that contains all nodes in the same tree as the context node. This node sequence is then filtered by subsequent steps in the path expression. If the context item is not a node, a dynamic error is raised.

3.2.1 Steps

[70]    StepExpr    ::=    AxisStep | FilterStep
[71]    AxisStep    ::=    (ForwardStep | ReverseStep) Predicates
[72]    FilterStep    ::=    PrimaryExpr Predicates
[82]    ForwardStep    ::=    (ForwardAxis NodeTest) | AbbreviatedForwardStep
[83]    ReverseStep    ::=    (ReverseAxis NodeTest) | AbbreviatedReverseStep

A step generates a sequence of items and then filters the sequence by zero or more predicates. The value of the step consists of those items that satisfy the predicates. Predicates are described in 3.2.2 Predicates. XQuery provides two kinds of step, called a filter step and an axis step.

A filter step consists simply of a primary expression followed by zero or more predicates. The result of the filter expression consists of all the items returned by the primary expression for which all the predicates are true. If no predicates are specified, the result is simply the result of the primary expression. This result may contain nodes, atomic values, or any combination of these. The ordering of the items returned by a filter step is the same as their order in the result of the primary expression.

The result of an axis step is always a sequence of zero or more nodes, and these nodes are always returned in document order. An axis step may be either a forward step or a reverse step, followed by zero or more predicates. An axis step might be thought of as beginning at the context node and navigating to those nodes that are reachable from the context node via a specified axis. Such a step has two parts: an axis, which defines the "direction of movement" for the step, and a node test, which selects nodes based on their kind, name, and/or type.

In the abbreviated syntax for a step, the axis can be omitted and other shorthand notations can be used as described in 3.2.4 Abbreviated Syntax.

The unabbreviated syntax for an axis step consists of the axis name and node test separated by a double colon. The result of the step consists of the nodes reachable from the context node via the specified axis that have the node kind, name, and/or type specified by the node test. For example, the step child::para selects the para element children of the context node: child is the name of the axis, and para is the name of the element nodes to be selected on this axis. The available axes are described in 3.2.1.1 Axes. The available node tests are described in 3.2.1.2 Node Tests. Examples of steps are provided in 3.2.3 Unabbreviated Syntax and 3.2.4 Abbreviated Syntax.

3.2.1.1 Axes
[86]    ForwardAxis    ::=    "child" "::"
| "descendant" "::"
| "attribute" "::"
| "self" "::"
| "descendant-or-self" "::"
[87]    ReverseAxis    ::=    "parent" "::"

XQuery supports the following axes:

  • the child axis contains the children of the context node

  • the descendant axis contains the descendants of the context node; a descendant is a child or a child of a child and so on; thus the descendant axis never contains attribute or namespace nodes

  • the parent axis contains the parent of the context node, if there is one

  • the attribute axis contains the attributes of the context node; the axis will be empty unless the context node is an element

  • the self axis contains just the context node itself

  • the descendant-or-self axis contains the context node and the descendants of the context node

Axes can be categorized as forward axes and reverse axes. An axis that only ever contains the context node or nodes that are after the context node in document order is a forward axis. An axis that only ever contains the context node or nodes that are before the context node in document order is a reverse axis.

In XQuery, the parent axis is a reverse axis; all other axes are forward axes. Since the self axis always contains at most one node, it makes no difference whether it is a forward or reverse axis.

3.2.1.2 Node Tests

A node test is a condition that must be true for each node selected by a step. The condition may be based on the kind of the node (element, attribute, text, document, comment, processing instruction, or namespace), the name of the node, or (in the case of element and attribute nodes), the type annotation of the node.

[88]    NodeTest    ::=    KindTest | NameTest
[89]    NameTest    ::=    QName | Wildcard
[90]    Wildcard    ::=    "*"
| NCName ":" "*"
| "*" ":" NCName
/* ws: explicit */

Every axis has a principal node kind. If an axis can contain elements, then the principal node kind is element; otherwise, it is the kind of nodes that the axis can contain. Thus:

  • For the attribute axis, the principal node kind is attribute.

  • For all other axes, the principal node kind is element.

A node test that consists of a QName is called a name test. A name test is true if and only if the kind of the node is the principal node kind and the expanded-QName of the node is equal to the expanded-QName specified by the name test. For example, child::para selects the para element children of the context node; if the context node has no para children, it selects an empty set of nodes. attribute::abc:href selects the attribute of the context node with the QName abc:href; if the context node has no such attribute, it selects an empty set of nodes.

A QName in a name test is expanded into an expanded-QName using the in-scope namespaces in the expression context. It is a static error if the QName has a prefix that does not correspond to any in-scope namespace. An unprefixed QName, when used as a name test on an axis whose principal node kind is element, has the namespaceURI of the default element namespace in the expression context; otherwise, it has no namespaceURI.

A name test is not satisfied by an element node whose name does not match the QName of the name test, even if it is in a substitution group whose head is the named element.

A node test * is true for any node of the principal node kind. For example, child::* will select all element children of the context node, and attribute::* will select all attributes of the context node.

A node test can have the form NCName:*. In this case, the prefix is expanded in the same way as with a QName, using the in-scope namespaces in the static context. If the prefix is not found in the in-scope namespaces, a static error is raised. The node test is true for any node of the principal node kind whose expanded-QName has the namespace URI to which the prefix is bound, regardless of the local part of the name.

A node test can also have the form *:NCName. In this case, the node test is true for any node of the principal node kind whose local name matches the given NCName, regardless of its namespace.

An alternative form of a node test is called a KindTest, which can select nodes based on their kind, name, and type annotation. The syntax and semantics of a KindTest are described in 2.4.3 SequenceType. When a KindTest is used in a node test, only those nodes on the designated axis that match the KindTest are selected. Shown below are several examples of KindTests that might be used in path expressions:

  • node() matches any node.

  • text() matches any text node.

  • comment() matches any comment node.

  • element() matches any element node.

  • element(person) matches any element node whose name is person (or is in the substitution group headed by person), and whose type annotation conforms to the top-level schema declaration for a person element.

  • element(person, *) matches any element node whose name is person (or is in the substitution group headed by person), without any restriction on type annotation.

  • element(person, surgeon) matches any element node whose name is person (or is in the substitution group headed by person), and whose type annotation is surgeon.

  • element(*, surgeon) matches any element node whose type annotation is surgeon, regardless of its name.

  • element(hospital/staff/person) matches any element node whose name and type annotation conform to the schema declaration of a person element in a staff element in a top-level hospital element.

  • attribute() matches any attribute node.

  • attribute(@price, *) matches any attribute whose name is price, regardless of its type annotation.

  • attribute(*, xs:decimal) matches any attribute whose type annotation is xs:decimal, regardless of its name.

  • document-node() matches any document node.

  • document-node(element(book)) matches any document node whose content consists of a single element node that satisfies the KindTest element(book).

3.2.2 Predicates

[74]    Predicates    ::=    ("[" Expr "]")*

A predicate consists of an expression, called a predicate expression, enclosed in square brackets. A predicate serves to filter a sequence, retaining some items and discarding others. For each item in the sequence to be filtered, the predicate expression is evaluated using an inner focus derived from that item, as described in 2.1.2 Evaluation Context. The result of the predicate expression is coerced to a Boolean value, called the predicate truth value, as described below. Those items for which the predicate truth value is true are retained, and those for which the predicate truth value is false are discarded.

The predicate truth value is derived by applying the following rules, in order:

  1. If the value of the predicate expression is an atomic value of a numeric type, the predicate truth value is true if the value of the predicate expression is equal to the context position, and is false otherwise.

  2. Otherwise, the predicate truth value is the Effective Boolean Value of the predicate expression.

Here are some examples of axis steps that contain predicates:

  • This example selects the second chapter element that is a child of the context node:

    child::chapter[2]
    
  • This example selects all the descendants of the context node whose name is "toy" and whose color attribute has the value "red":

    descendant::toy[attribute::color = "red"]
    
  • This example selects all the employee children of the context node that have a secretary subelement:

    child::employee[secretary]
    

Here are some examples of filter steps that contain predicates:

  • List all the integers from 1 to 100 that are divisible by 5. (See 3.3.1 Constructing Sequences for an explanation of the to operator.)

    (1 to 100)[. mod 5 eq 0]
    
  • The result of the following expression is the integer 95:

    (99 to 0)[5]
    

3.2.3 Unabbreviated Syntax

This section provides a number of examples of path expressions in which the axis is explicitly specified in each step. The syntax used in these examples is called the unabbreviated syntax. In many common cases, it is possible to write path expressions more concisely using an abbreviated syntax, as explained in 3.2.4 Abbreviated Syntax.

  • child::para selects the para element children of the context node

  • child::* selects all element children of the context node

  • child::text() selects all text node children of the context node

  • child::node() selects all the children of the context node, whatever their node type

  • attribute::name selects the name attribute of the context node

  • attribute::* selects all the attributes of the context node

  • parent::* selects the parent of the context node. If the context node is an attribute node, this expression returns the element node (if any) to which the attribute node is attached.

  • descendant::para selects the para element descendants of the context node

  • descendant-or-self::para selects the para element descendants of the context node and, if the context node is a para element, the context node as well

  • self::para selects the context node if it is a para element, and otherwise selects nothing

  • child::chapter/descendant::para selects the para element descendants of the chapter element children of the context node

  • child::*/child::para selects all para grandchildren of the context node

  • / selects the root of the node hierarchy that contains the context node

  • /descendant::para selects all the para elements in the same document as the context node

  • /descendant::list/child::member selects all the member elements that have a list parent and that are in the same document as the context node

  • child::para[fn:position() = 1] selects the first para child of the context node

  • child::para[fn:position() = fn:last()] selects the last para child of the context node

  • child::para[fn:position() = fn:last()-1] selects the last but one para child of the context node

  • child::para[fn:position() > 1] selects all the para children of the context node other than the first para child of the context node

  • /descendant::figure[fn:position() = 42] selects the forty-second figure element in the document

  • /child::doc/child::chapter[fn:position() = 5]/child::section[fn:position() = 2]selects the second section of the fifth chapter of the doc document element

  • child::para[attribute::type="warning"]selects all para children of the context node that have a type attribute with value warning

  • child::para[attribute::type='warning'][fn:position() = 5]selects the fifth para child of the context node that has a type attribute with value warning

  • child::para[fn:position() = 5][attribute::type="warning"]selects the fifth para child of the context node if that child has a type attribute with value warning

  • child::chapter[child::title='Introduction']selects the chapter children of the context node that have one or more title children with string-value equal to Introduction

  • child::chapter[child::title] selects the chapter children of the context node that have one or more title children

  • child::*[self::chapter or self::appendix] selects the chapter and appendix children of the context node

  • child::*[self::chapter or self::appendix][fn:position() = fn:last()] selects the last chapter or appendix child of the context node

3.2.4 Abbreviated Syntax

[84]    AbbreviatedForwardStep    ::=    "." | ("@" NameTest) | NodeTest
[85]    AbbreviatedReverseStep    ::=    ".."

The abbreviated syntax permits the following abbreviations:

  1. The most important abbreviation is that the axis name can be omitted from an axis step. If the axis name is omitted from an axis step, the default axis is child unless the axis step contains an AttributeTest; in that case, the default axis is attribute. For example, a path expression section/para is an abbreviation for child::section/child::para. Similarly, section/attribute(@id) is an abbreviation for child::section/attribute::attribute(@id).

  2. There is also an abbreviation for attributes: attribute:: can be abbreviated by @. For example, a path expression para[@type="warning"] is short for child::para[attribute::type="warning"] and so selects para children with a type attribute with value equal to warning.

  3. // is effectively replaced by /descendant-or-self::node()/ during processing of a path expression. For example, //para is an abbreviation for /descendant-or-self::node()/child::para and so will select any para element in the document (even a para element that is a document element will be selected by //para since the document element node is a child of the root node); div1//para is short for div1/descendant-or-self::node()/child::para and so will select all para descendants of div1 children.

    Note that the path expression //para[1] does not mean the same as the path expression /descendant::para[1]. The latter selects the first descendant para element; the former selects all descendant para elements that are the first para children of their parents.

  4. A step consisting of . returns the context item. This is particularly useful in conjunction with the // operator. For example, the path expression .//para returns all para descendant elements of the context node.

  5. A step consisting of .. is short for parent::node(). For example, ../title is short for parent::node()/child::title and so will select the title children of the parent of the context node.

Here are some examples of path expressions that use the abbreviated syntax:

  • para selects the para element children of the context node

  • * selects all element children of the context node

  • text() selects all text node children of the context node

  • @name selects the name attribute of the context node

  • @* selects all the attributes of the context node

  • para[1] selects the first para child of the context node

  • para[fn:last()] selects the last para child of the context node

  • */para selects all para grandchildren of the context node

  • /doc/chapter[5]/section[2] selects the second section of the fifth chapter of the doc

  • chapter//para selects the para element descendants of the chapter element children of the context node

  • //para selects all the para descendants of the document root and thus selects all para elements in the same document as the context node

  • //list/member selects all the member elements in the same document as the context node that have a list parent

  • . selects the context item

  • .//para selects the para element descendants of the context node

  • .. selects the parent of the context node

  • ../@lang selects the lang attribute of the parent of the context node

  • para[@type="warning"] selects all para children of the context node that have a type attribute with value warning

  • para[@type="warning"][5] selects the fifth para child of the context node that has a typeattribute with value warning

  • para[5][@type="warning"] selects the fifth para child of the context node if that child has a type attribute with value warning

  • chapter[title="Introduction"] selects the chapter children of the context node that have one or more title children with string-value equal to Introduction

  • chapter[title] selects the chapter children of the context node that have one or more title children

  • employee[@secretary and @assistant] selects all the employee children of the context node that have both a secretary attribute and an assistant attribute

  • book/(chapter|appendix)/section selects every section element that has a parent that is either a chapter or an appendix element, that in turn is a child of a book element that is a child of the context node.

  • book/fn:id(publisher)/name returns the same result as fn:id(book/publisher)/name.

  • If E is any expression that returns a sequence of nodes, then the expression E/. returns the same nodes in document order, with duplicates eliminated based on node identity.

3.3 Sequence Expressions

XQuery supports operators to construct and combine sequences. A sequence is an ordered collection of zero or more items. An item may be an atomic value or a node. An item is identical to a sequence of length one containing that item. Sequences are never nested--for example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3).

3.3.1 Constructing Sequences

[39]    Expr    ::=    ExprSingle ("," ExprSingle)*
[61]    RangeExpr    ::=    AdditiveExpr ( "to" AdditiveExpr )?

One way to construct a sequence is by using the comma operator, which evaluates each of its operands and concatenates the resulting values, in order, into a single result sequence. Empty parentheses can be used to denote an empty sequence. In places where the grammar calls for ExprSingle, such as the arguments of a function call, any expression that contains a top-level comma operator must be enclosed in parentheses.

A sequence may contain duplicate values or nodes, but a sequence is never an item in another sequence. When a new sequence is created by concatenating two or more input sequences, the new sequence contains all the items of the input sequences and its length is the sum of the lengths of the input sequences.

Here are some examples of expressions that construct sequences:

  • This expression is a sequence of five integers:

    (10, 1, 2, 3, 4)
    
  • This expression constructs one sequence from the sequences 10, (1, 2), the empty sequence (), and (3, 4):

    (10, (1, 2), (), (3, 4))
    

    It evaluates to the sequence:

    10, 1, 2, 3, 4

  • This expression contains all salary children of the context node followed by all bonus children:

    (salary, bonus)
    
  • Assuming that $price is bound to the value 10.50, this expression:

    ($price, $price)
    

    evaluates to the sequence

    10.50, 10.50

A RangeExpr can be used to construct a sequence of consecutive integers. Each of the operands of the to operator is converted as though it was an argument of a function with the expected parameter type xs:integer (this process raises an error if the operand cannot be converted to a single integer). A sequence is constructed containing the two integer operands and every integer between the two operands. If the first operand is less than the second, the sequence is in increasing order, otherwise it is in decreasing order.

  • This example uses a range expression as one operand in constructing a sequence:

    (10, 1 to 4)
    

    It evaluates to the sequence:

    10, 1, 2, 3, 4

  • This example constructs a sequence of length one:

    10 to 10
    

    It evaluates to a sequence consisting of the single integer 10.

3.3.2 Combining Sequences

[65]    UnionExpr    ::=    IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )*
[66]    IntersectExceptExpr    ::=    ValueExpr ( ("intersect" | "except") ValueExpr )*
[67]    ValueExpr    ::=    ValidateExpr | PathExpr

XQuery provides several operators for combining sequences of nodes. The union and | operators are equivalent. They take two node sequences as operands and return a sequence containing all the nodes that occur in either of the operands. The intersect operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in both operands. The except operator takes two node sequences as operands and returns a sequence containing all the nodes that occur in the first operand but not in the second operand. All of these operators return their result sequences in document order without duplicates based on node identity. If an operand of union, intersect, or except contains an item that is not a node, a type error is raised.

Here are some examples of expressions that combine sequences. Assume the existence of three element nodes that we will refer to by symbolic names A, B, and C. Assume that $seq1 is bound to a sequence containing A and B, $seq2 is also bound to a sequence containing A and B, and $seq3 is bound to a sequence containing B and C. Then:

  • $seq1 union $seq1 evaluates to a sequence containing A and B.

  • $seq2 union $seq3 evaluates to a sequence containing A, B, and C.

  • $seq1 intersect $seq1 evaluates to a sequence containing A and B.

  • $seq2 intersect $seq3 evaluates to a sequence containing B only.

  • $seq1 except $seq2 evaluates to the empty sequence.

  • $seq2 except $seq3 evaluates to a sequence containing A only.

In addition to the sequence operators described here,[XQuery 1.0 and XPath 2.0 Functions and Operators] includes functions for indexed access to items or sub-sequences of a sequence, for indexed insertion or removal of items in a sequence, and for removing duplicate values or nodes from a sequence.

3.4 Arithmetic Expressions

XQuery provides arithmetic operators for addition, subtraction, multiplication, division, and modulus, in their usual binary and unary forms.

[62]    AdditiveExpr    ::=    MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )*
[63]    MultiplicativeExpr    ::=    UnaryExpr ( ("*" | "div" | "idiv" | "mod") UnaryExpr )*
[64]    UnaryExpr    ::=    ("-" | "+")* UnionExpr

The binary subtraction operator must be preceded by whitespace if it could otherwise be interpreted as part of the previous token. For example, a-b will be interpreted as a name, but a - b will be interpreted as an arithmetic operation.

An arithmetic expression is evaluated by applying the following rules, in order, until an error is raised or a value is computed:

  1. Atomization is applied to each operand.

  2. If either operand is now an empty sequence, the result of the operation is an empty sequence.

  3. If either operand is now a sequence of length greater than one, a type error is raised.

  4. If either operand is now of type xdt:untypedAtomic, it is cast to the default type for the given operator. The default type for the idiv operator is xs:integer; the default type for all other arithmetic operators is xs:double. If the cast fails, a type error is raised.

  5. If the operand types are now valid for the given operator, the operator is applied to the operands, resulting in an atomic value or a dynamic error (for example, an error might result from dividing by zero.) The combinations of atomic types that are accepted by the various arithmetic operators, and their respective result types, are listed in B.2 Operator Mapping together with the functions in [XQuery 1.0 and XPath 2.0 Functions and Operators] that define the semantics of the operation for each type.

  6. If the operand types are still not valid for the given operator, a type error is raised.

XQuery supports two division operators named div and idiv. The div operator accepts operands of any numeric types. The type of the result of the div operator is the least common type of its operands; however, if both operands are of type xs:integer, div returns a result of type xs:decimal. The idiv operator, on the other hand, requires its operands to be of type xs:integer and returns a result of type xs:integer, rounded toward zero.

Here are some examples of arithmetic expressions:

  • The first expression below returns -1.5, and the second expressions returns -1:

    -3 div 2
    -3 idiv 2
    
  • Subtraction of two date values results in a value of type xdt:dayTimeDuration:

    $emp/hiredate - $emp/birthdate
    
  • This example illustrates the difference between a subtraction operator and a hyphen:

    $unit-price - $unit-discount
    
  • Unary operators have higher precedence than binary operators, subject of course to the use of parentheses:

    -($bellcost + $whistlecost)
    

3.5 Comparison Expressions

Comparison expressions allow two values to be compared. XQuery provides four kinds of comparison expressions, called value comparisons, general comparisons, node comparisons, and order comparisons.

[60]    ComparisonExpr    ::=    RangeExpr ( (ValueComp
| GeneralComp
| NodeComp
| OrderComp) RangeExpr )?
[79]    ValueComp    ::=    "eq" | "ne" | "lt" | "le" | "gt" | "ge"
[78]    GeneralComp    ::=    "=" | "!=" | "<" | "<=" | ">" | ">="
[80]    NodeComp    ::=    "is" | "isnot"
[81]    OrderComp    ::=    "<<" | ">>"

3.5.1 Value Comparisons

Value comparisons are intended for comparing single values. The result of a value comparison is defined by applying the following rules, in order:

  1. Atomization is applied to each operand. If the result, called an atomized operand, does not contain exactly one atomic value, a type error is raised.

  2. Any atomized operand that has the dynamic type xdt:untypedAtomic is cast to the type xs:string.

  3. The result of the comparison is true if the value of the first operand is (equal, not equal, less than, less than or equal, greater than, greater than or equal) to the value of the second operand; otherwise the result of the comparison is false. B.2 Operator Mapping describes which combinations of atomic types are comparable, and how comparisons are performed on values of various types. If the value of the first atomized operand is not comparable with the value of the second atomized operand, a type error is raised.

Here are some examples of value comparisons:

  • The following comparison is true only if $book1 has a single author subelement and its value is "Kennedy":

    $book1/author eq "Kennedy"
    
  • The following comparison is true because the two constructed nodes have the same value after atomization, even though they have different identities:

    <a>5</a> eq <a>5</a>
    
  • The following comparison is true if hatsize and shoesize are both user-defined types that are derived by restriction from a primitive numeric type:

    hatsize(5) eq shoesize(5)
    

3.5.2 General Comparisons

General comparisons are existentially quantified comparisons that may be applied to operand sequences of any length. The result of a general comparison that does not raise an error is always true or false.

Atomization is applied to each operand of a general comparison. The result of the comparison is true if and only if there is a pair of atomic values, one belonging to the result of atomization of the first operand and the other belonging to the result of atomization of the second operand, that have the required magnitude relationship. Otherwise the result of the general comparison is false. The magnitude relationship between two atomic values is determined as follows:

  1. If either atomic value has the dynamic type xdt:untypedAtomic, that value is cast to a required type, which is determined as follows:

    1. If the dynamic type of the other atomic value is a numeric type, the required type is xs:double.

    2. If the dynamic type of the other atomic value is xdt:untypedAtomic, the required type is xs:string.

    3. Otherwise, the required type is the dynamic type of the other atomic value.

    If the cast to the required type fails, a dynamic error is raised.

  2. After any necessary casting, the atomic values are compared using one of the value comparison operators eq, ne, lt, le, gt, or ge, depending on whether the general comparison operator was =, !=, <, <=, >, or >=. The values have the required magnitude relationship if the result of this value comparison is true.

When evaluating a general comparison in which either operand is a sequence of items, an implementation may return true as soon as it finds an item in the first operand and an item in the second operand for which the underlying value comparison is true. Similarly, a general comparison may raise a dynamic error as soon as it encounters an error in evaluating either operand, or in comparing a pair of items from the two operands. As a result of these rules, the result of a general comparison is not deterministic in the presence of errors.

Here are some examples of general comparisons:

  • The following comparison is true if the value of any author subelement of $book1 has the string value "Kennedy":

    $book1/author = "Kennedy"
    
  • The following example contains three general comparisons. The value of the first two comparisons is true, and the value of the third comparison is false. This example illustrates the fact that general comparisons are not transitive.

    (1, 2) = (2, 3)
    (2, 3) = (3, 4)
    (1, 2) = (3, 4)
    
  • Suppose that $a, $b, and $c are bound to element nodes with type annotation xdt:untypedAtomic, with string values "1", "2", and "2.0" respectively. Then ($a, $b) = ($c, 3.0) returns false, because $b and $c are compared as strings. However, ($a, $b) = ($c, 2.0) returns true, because $b and 2.0 are compared as numbers.

3.5.3 Node Comparisons

The result of a node comparison is defined by applying the following rules, in order:

  1. Each operand must be either a single node or an empty sequence; otherwise a type error is raised.

  2. If either operand is an empty sequence, the result of the comparison is an empty sequence.

  3. A comparison with the is operator is true if the two operands are nodes that have the same identity; otherwise it is false. A comparison with the isnot operator is true if the two operands are nodes that have different identities; otherwise it is false. See [XQuery 1.0 and XPath 2.0 Data Model] for a discussion of node identity.

Use of the is operator is illustrated below.

  • The following comparison is true only if the left and right sides each evaluate to exactly the same single node:

    //book[isbn="1558604820"] is //book[call="QA76.9 C3845"]
    
  • The following comparison is false because each constructed node has its own identity:

    <a>5</a> is <a>5</a>
    

3.5.4 Order Comparisons

The result of an order comparison is defined by applying the following rules, in order:

  1. Both operands must be either a single node or an empty sequence; otherwise a type error is raised.

  2. If either operand is an empty sequence, the result of the comparison is an empty sequence.

  3. A comparison with the << operator returns true if the first operand node is earlier than the second operand node in document order; otherwise it returns false.

  4. A comparison with the >> operator returns true if the first operand node is later than the second operand node in document order; otherwise it returns false.

Here is an example of an order comparison:

  • The following comparison is true only if the node identified by the left side occurs before the node identified by the right side in document order:

    //purchase[parcel="28-451"] << //sale[parcel="33-870"]
    

3.6 Logical Expressions

A logical expression is either an and-expression or an or-expression. If a logical expression does not raise an error, its value is always one of the boolean values true or false.

Logical Expressions
[54]    OrExpr    ::=    AndExpr ( "or" AndExpr )*
[55]    AndExpr    ::=    InstanceofExpr ( "and" InstanceofExpr )*

The first step in evaluating a logical expression is to find the effective boolean value of each of its operands (see 2.4.4.2 Effective Boolean Value).

The value of an and-expression is determined by the effective boolean values (EBV's) of its operands. If an error is raised during computation of one of the effective boolean values, an and-expression may raise a dynamic error, as shown in the following table:

AND: EBV2 = true EBV2 = false error in EBV2
EBV1 = true true false error
EBV1 = false false false false or error
error in EBV1 error false or error error

The value of an or-expression is determined by the effective boolean values (EBV's) of its operands. If an error is raised during computation of one of the effective boolean values, an or-expression may raise a dynamic error, as shown in the following table:

OR: EBV2 = true EBV2 = false error in EBV2
EBV1 = true true true true or error
EBV1 = false true false error
error in EBV1 true or error error error

The order in which the operands of a logical expression are evaluated is implementation-dependent. The tables above are defined in such a way that an or-expression can return true if the first expression evaluated is true, and it can raise an error if evaluation of the first expression raises an error. Similarly, an and-expression can return false if the first expression evaluated is false, and it can raise an error if evaluation of the first expression raises an error. As a result of these rules, a logical expression is not deterministic in the presence of errors, as illustrated in the examples below.

Here are some examples of logical expressions:

  • The following expressions return true:

    1 eq 1 and 2 eq 2
    
    1 eq 1 or 2 eq 3
    
  • The following expression may return either false or raise a dynamic error:

    1 eq 2 and 3 idiv 0 = 1
    
  • The following expression may return either true or raise a dynamic error:

    1 eq 1 or 3 idiv 0 = 1
    
  • The following expression must raise a dynamic error:

    1 eq 1 and 3 idiv 0 = 1
    

In addition to and- and or-expressions, XQuery provides a function named not that takes a general sequence as parameter and returns a boolean value. The not function reduces its parameter to an effective boolean value. It then returns true if the effective boolean value of its parameter is false, and false if the effective boolean value of its parameter is true. If an error is encountered in finding the effective boolean value of its operand, not raises a dynamic error. The not function is described in [XQuery 1.0 and XPath 2.0 Functions and Operators].

3.7 Constructors

XQuery provides constructors that can create XML structures within a query. Constructors are provided for every kind of node in the Data Model ([XQuery 1.0 and XPath 2.0 Data Model]) except namespace nodes. A special form of constructor called a computed constructor can be used to create an element or attribute with a computed name or to create a document node or a text node.

[77]    Constructor    ::=    ElementConstructor
| XmlComment
| XmlProcessingInstruction
| CdataSection
| ComputedDocumentConstructor
| ComputedElementConstructor
| ComputedAttributeConstructor
| ComputedTextConstructor
[95]    ElementConstructor    ::=    "<" QName AttributeList ("/>" | (">" ElementContent* "</" QName S? ">")) /* ws: explicit */
/* pn: lt */
[27]    ElementContentChar    ::=    Char - [{}<&]
[103]    ElementContent    ::=    ElementContentChar
| "{{"
| "}}"
| ElementConstructor
| EnclosedExpr
| CdataSection
| CharRef
| PredefinedEntityRef
| XmlComment
| XmlProcessingInstruction
/* ws: significant */
[104]    AttributeList    ::=    (S (QName S? "=" S? AttributeValue)?)* /* ws: explicit */
[105]    AttributeValue    ::=    ('"' (EscapeQuot | AttributeValueContent)* '"')
| ("'" (EscapeApos | AttributeValueContent)* "'")
/* ws: significant */
[106]    AttributeValueContent    ::=    QuoteAttributeContentChar
| AposAttributeContentChar
| CharRef
| "{{"
| "}}"
| EnclosedExpr
| PredefinedEntityRef
/* ws: significant */
[28]    QuoteAttributeContentChar    ::=    Char - ["{}<&]
[29]    AposAttributeContentChar    ::=    Char - ['{}<&]
[25]    EscapeApos    ::=    "''"
[107]    EnclosedExpr    ::=    "{" Expr "}"

This section contains a conceptual description of the semantics of various kinds of constructor expressions. An XQuery implementation is free to use any implementation technique that produces the same result as the processing steps described in this section.

3.7.1 Direct Element Constructors

An element constructor creates an XML element. If the name, attributes, and content of the element are all constants, the element constructor is based on standard XML notation and is called a direct element constructor. For example, the following expression is a direct element constructor that creates a book element containing attributes, subelements, and text:

<book isbn="isbn-0060229357">
    <title>Harold and the Purple Crayon</title>
    <author>
        <first>Crockett</first>
        <last>Johnson</last>
    </author>
</book>

Unqualified element names used in a direct element constructor are implicitly qualified by the default namespace for element names. In a direct element constructor, the name used in the end tag must exactly match the name used in the corresponding start tag, including its prefix or absence of a prefix.

In a direct element constructor, curly braces { } delimit enclosed expressions, distinguishing them from literal text. Enclosed expressions are evaluated and replaced by their value, whereas material outside curly braces is simply treated as literal text, as illustrated by the following example:

<example>
   <p> Here is a query. </p>
   <eg> $i//title </eg>
   <p> Here is the result of the query. </p>
   <eg>{ $i//title }</eg>
</example>

The above query might generate the following result (whitespace has been added for readability to this result and other result examples in this document):

<example>
  <p> Here is a query. </p>
  <eg> $i//title </eg>
  <p> Here is the result of the query. </p>
  <eg><title>Harold and the Purple Crayon</title></eg>
</example>

Since XQuery uses curly braces to denote enclosed expressions, some convention is needed to denote a curly brace used as an ordinary character. For this purpose, a pair of identical curly brace characters within the content of an element or attribute are interpreted by XQuery as a single curly brace character (that is, the pair "{{" represents the character "{" and the pair "}}" represents the character "}".) A single left curly brace ("{") is interpreted as the beginning delimiter for an enclosed expression. A single right curly brace ("}") without a matching left curly brace is treated as an error.

The result of an element constructor is a new element node, with its own node identity. All the attribute and descendant nodes of the new element node are also new nodes with their own identities, even though they may be copies of existing nodes.

3.7.1.1 Attributes

The start tag of a direct element constructor may contain one or more attributes. As in XML, each attribute is specified by a name and a value. In a direct element constructor, the name of each attribute is specified by a constant QName, and the value of the attribute is specified by a string of characters enclosed in single or double quotes. As in the main content of the element constructor, an attribute value may contain expressions enclosed in curly braces, which are evaluated and replaced by their value during processing of the element constructor.

Each attribute in a direct element constructor creates a new attribute node, with its own node identity, whose parent is the constructed element node. (Exception: namespace declaration attributes (see 3.7.1.2 Namespaces) do not create attribute nodes.) All the attribute nodes generated by an element constructor must have distinct names.

Conceptually, an attribute (other than a namespace declaration attribute) in a direct element constructor is processed by the following steps:

  1. Predefined entity references and character references in the attribute content are expanded into their referenced strings, as described in 3.1.1 Literals.

  2. Each consecutive sequence of literal characters in the attribute content is treated as a string containing those characters. Whitespace in attribute content is normalized according to the rules for "Attribute Value Normalization" in [XML] (each whitespace character is replaced by a space (#x20) character.)

  3. Each enclosed expression is converted to a string as follows:

    1. Atomization is applied to the value of the enclosed expression, converting it to a sequence of atomic values.

    2. If the result of atomization is an empty sequence, the result is the zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string.

    3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair.

  4. Adjacent strings resulting from the above steps are concatenated with no intervening blanks. The resulting string becomes the value of the attribute.

  • Example:

    <shoe size="7"/>
    

    The value of the size attribute is "7".

  • Example:

    <shoe size="{7}"/>
    

    The value of the size attribute is "7".

  • Example:

    <shoe size="{()}"/>
    

    The value of the size attribute is the zero-length string.

  • Example:

    <chapter ref="[{1, 5 to 7, 9}]"/>
    

    The value of the ref attribute is "[1 5 6 7 9]".

  • Example:

    <shoe size="As big as {$hat/@size}"/>
    

    The value of the size attribute is the string "As big as ", concatenated with the string value of the node denoted by the expression $hat/@size.

3.7.1.2 Namespaces

The names used inside an element constructor may be qualified names that include namespace prefixes. Namespace prefixes can be bound to namespaces in the Prolog or in namespace declaration attributes. It is a static error to use a namespace prefix that has not been bound to a namespace.

A namespace declaration attribute serves to define a namespace prefix for use within the scope of an element constructor. A namespace declaration attribute always has the name xmlns or a QName with the prefix xmlns. If the value of a namespace declaration attribute is not a literal string, a static error is raised. A namespace declaration attribute does not cause an attribute node to be created. Namespace declaration attributes are discussed further in 4.2 Namespace Declarations and [XML Names]. The following element constructor illustrates the use of namespace declaration attributes that define the namespace prefixes metric and english:

<box xmlns:metric = "http://example.org/metric/units"
     xmlns:english = "http://example.org/english/units">
  <height> <metric:meters>3</metric:meters> </height>
  <width> <english:feet>6</english:feet> </width>
  <depth> <english:inches>18</english:inches> </depth>
</box>
Editorial note  
The namespace nodes to be generated in conjunction with the new element node have not yet been defined.
3.7.1.3 Content

The part of a direct element constructor between the start tag and the end tag is called the content of the element constructor. This content may consist of literal text characters, nested element constructors, and expressions enclosed in curly braces. In general, the value of an enclosed expression may be any sequence of nodes and/or atomic values. Enclosed expressions can be used in the content of an element constructor to compute both the content and the attributes of the constructed node.

Conceptually, the content of an element constructor is processed as follows:

  1. The content is evaluated to produce a sequence of nodes called the content sequence, as follows:

    1. Predefined entity references and character references are expanded into their referenced strings, as described in 3.1.1 Literals.

    2. Each consecutive sequence of literal characters evaluates to a single text node containing the characters. However, if the sequence consists entirely of boundary whitespace as defined in 3.7.1.4 Whitespace in Element Content and the Prolog does not specify xmlspace = preserve, then no text node is generated.

    3. Each nested element constructor is evaluated according to the rules in this section, resulting in a new element node.

    4. Enclosed expressions are evaluated as follows: For each node returned by an enclosed expression, a new deep copy of the node is constructed, including all its children, attributes, and namespace nodes (if any). Each copied node has a new node identity. Copied element nodes are given the type annotation xs:anyType, and copied attribute nodes are given the type annotation xs:anySimpleType. For each adjacent sequence of one or more atomic values returned by an enclosed expression, a new text node is constructed, containing the result of casting each atomic value to a string, with a single blank character inserted between adjacent values.

  2. If the content sequence contains a document node, a type error is raised.

  3. If the content sequence contains an attribute node following a node that is not an attribute node, a type error is raised. Attribute nodes occurring at the beginning of the content sequence become attributes of the new element node. If two or more attributes of the new element node have the same name, an error is raised.

  4. Adjacent text nodes in the content sequence are coalesced into a single text node by concatenating their contents, with no intervening blanks.

  5. The resulting sequence of nodes becomes the children and attributes of the new element node in the Data Model representation.

  6. The new element node is automatically validated, as described in 3.7.1.5 Type of a Constructed Element.

  • Example:

    <a>{1}</a>
    

    The constructed element node has one child, a text node containing the value "1".

  • Example:

    <a>{1, 2, 3}</a>
    

    The constructed element node has one child, a text node containing the value "1 2 3".

  • Example:

    <c>{1}{2}{3}</c>
    

    The constructed element node has one child, a text node containing the value "123".

  • Example:

    <b>{1, "2", "3"}</b>
    

    The constructed element node has one child, a text node containing the value "1 2 3".

  • Example:

    <fact>I saw 8 cats.</fact>
    

    The constructed element node has one child, a text node containing the value "I saw 8 cats.".

  • Example:

    <fact>I saw {5 + 3} cats.</fact>
    

    The constructed element node has one child, a text node containing the value "I saw 8 cats.".

  • Example:

    <fact>I saw <howmany>{5 + 3}</howmany> cats.</fact>
    

    The constructed element node has three children: a text node containing "I saw ", a child element node named howmany, and a text node containing " cats.". The child element node in turn has a single text node child containing the value "8".

3.7.1.4 Whitespace in Element Content

In a direct element constructor, whitespace characters may appear in element content. In some cases, enclosed expressions and/or nested elements may be separated only by whitespace characters. For example, in the expression below, the end-tag </title> and the start-tag <author> are separated by a newline character and four space characters:

<book isbn="isbn-0060229357">
    <title>Harold and the Purple Crayon</title>
    <author>
        <first>Crockett</first>
        <last>Johnson</last>
    </author>
</book>

We will refer to whitespace characters that occur by themselves in the boundaries between tags and/or enclosed expressions, as in the above example, as boundary whitespace. The Prolog contains a declaration called xmlspace that controls whether boundary whitespace is preserved by element constructors. If xmlspace is not declared in the prolog or is declared as xmlspace = strip, boundary whitespace is not considered significant and is discarded. On the other hand, if xmlspace = preserve is declared in the prolog, boundary whitespace is considered significant and is preserved.

  • Example:

    <cat>
       <breed>{$b}</breed>
       <color>{$c}</color>
    </cat>
    

    The constructed cat element node has two child element nodes named breed and color. Whitespace surrounding the child elements has been stripped away by the element constructor (assuming that the Prolog did not specify xmlspace = preserve.)

  • Example:

    <a>  {"abc"}  </a>
    

    If xmlspace is not declared or is declared as xmlspace = strip, this example is equivalent to <a>abc</a>. However, if xmlspace = preserve is declared, this example is equivalent to <a>  abc  </a>.

  • Example:

    <a> z {"abc"}</a>
    

    Since the whitespace surrounding the z is not boundary whitespace, it is always preserved. This example is equivalent to <a> z abc</a>.

For the purpose of the above rule, whitespace characters generated by character references such as &#x20; are not considered to be boundary whitespace, and are always preserved.

  • Example:

    <a>&#x20;{"abc"}</a>
    

    This example is equivalent to <a> abc</a>, regardless of the declaration of xmlspace.

It is important to remember that whitespace generated by an enclosed expression is never considered to be boundary whitespace, and is always preserved.

  • Example:

    <a>{"  "}</a>
    

    This example is equivalent to <a>  </a>, regardless of the declaration of xmlspace.

3.7.1.5 Type of a Constructed Element

A direct element constructor automatically validates the newly constructed element, using the schema validation process described in [XML Schema]. The validation process results in a type annotation for the element node and for each of its attribute nodes. The validation process may also result in adding additional attributes, with default values, to the constructed element. Validation is performed using the validation mode and validation context from the static context of the element constructor, according to the following rules:

  • If validation mode = skip, no validation is attempted. The constructed element node is given a type annotation of xs:anyType, and each of its attributes is given a type annotation of xdt:untypedAtomic.

  • If validation mode = strict, the in-scope element declarations are searched for an element declaration whose unique name matches the name of the constructed element, as interpreted in the validation context of the element constructor. If no such element declaration is found, validation fails and an error is raised (if the name of the constructed element is known statically, this can be a static error). If such an element declaration is found, the newly constructed element is converted to an Infoset representation using the rules for "Data Model to Infoset Mapping" in [XQuery 1.0 and XPath 2.0 Data Model]. The resulting Infoset is then validated according to the rules for "Assessing Schema Validity" in [XML Schema]. This validation process results in a Post-Schema Validation Infoset (PSVI). If, in this PSVI, the [validity] property of the constructed element is valid, then the PSVI is converted back into a Data Model representation, using the rules for "PSVI to Data Model Mapping" in [XQuery 1.0 and XPath 2.0 Data Model]. Otherwise, validation fails and a dynamic error is raised.

  • If validation mode = lax, the in-scope element declarations are searched for an element declaration that matches the name of the constructed element, as interpreted in the validation context of the element constructor. If such an element declaration is found, the constructed element is processed as though validation mode = strict; otherwise it is processed as though validation mode = skip.

A direct element constructor adds the name of the constructed element to the validation context for expressions that are nested inside the element constructor. This process is illustrated by the following example:

<customer>
   <hat>{7}</hat>
   <shoe>{"8"}</shoe>
</customer>

If <customer> is the outermost element constructor in the query, it is validated with a global validation context. However, it adds the name of the constructed element to the validation context for nested expressions, causing <hat> and <shoe> to be validated with the validation context /customer.

It is important to understand that the type annotation of a constructed element may be different from the type of the expression from which the element was constructed. In the above example, the hat element was constructed from an expression of type xs:integer, and the shoe element was constructed from an expression of type xs:string. If validation mode = skip, then after validation the hat and shoe elements will both have a type annotation of xs:anyType. However, if validation mode = strict, then after validation the hat and shoe elements will have type annotations that are derived from their element declarations--possibly schema-defined types such as hatsize and shoesize.

The validation process for a constructed element may be affected by the presence of an xsi:type attribute. For example, the following constructed element has an attribute that causes it to be validated as an integer:

<a xsi:type="xs:integer">47</a>

3.7.2 Computed Constructors

An alternative way to create nodes is by using a computed constructor. A computed constructor begins with a keyword that identifies the type of node to be created: element, attribute, document, or text. The keyword element or attribute is followed by the name of the node to be created (document and text nodes have no name). The name of an element or attribute may be specified either by a QName or by an expression enclosed in braces, called the name expression, that returns a QName. The final part of a computed constructor is an expression enclosed in braces, called the content expression, that generates the content of the node.

[97]    ComputedElementConstructor    ::=    ("element" QName "{" | ("element" "{" Expr "}" "{")) Expr? "}"
[98]    ComputedAttributeConstructor    ::=    ("attribute" QName "{" | ("attribute" "{" Expr "}" "{")) Expr? "}"
[96]    ComputedDocumentConstructor    ::=    "document" "{" Expr "}"
[99]    ComputedTextConstructor    ::=    "text" "{" Expr? "}"

The following example illustrates the use of computed element and attribute constructors in a simple case where the names of the constructed nodes are constants. This example generates exactly the same result as the first example in 3.7.1 Direct Element Constructors:

element book 
{
    attribute isbn { "isbn-0060229357" },
    element title { "Harold and the Purple Crayon" },
    element author 
    {
        element first { "Crockett" },
        element last { "Johnson" }
    }
}
3.7.2.1 Computed Element Constructors

The name expression of a computed element constructor is processed as follows:

  1. If the name expression returns an expanded QName, that QName is used as the name of the constructed element.

  2. If the name expression returns a string, that string is cast to a QName and its prefix is expanded using the in-scope namespaces. The resulting expanded QName is used as the name of the constructed element. If casting of the string to a QName or expansion of its prefix is not successful, a dynamic error is raised.

  3. If the name expression does not return a QName or a string, a type error is raised.



The content expression of a computed element constructor is processed as follows:

  1. For each node returned by the content expression, a new deep copy of the node is constructed, including all its children, attributes, and namespace nodes (if any). Each copied node has a new node identity. Copied element nodes are given the type annotation xs:anyType, and copied attribute nodes are given the type annotation xs:anySimpleType. For each adjacent sequence of one or more atomic values returned by the content expression, a new text node is constructed, containing the result of casting each atomic value to a string, with a single blank character inserted between adjacent values. The resulting sequence of nodes is called the content sequence.

  2. If the content sequence contains a document node, a type error is raised.

  3. If the content sequence contains an attribute node following a node that is not an attribute node, a type error is raised. Attribute nodes occurring at the beginning of the content sequence become attributes of the new element node. If two or more of these attribute nodes have the same name, an error is raised.

  4. Element, text, comment, and processing instruction nodes in the content sequence become the children of the constructed element node.

A computed element constructor automatically validates the constructed node, using the validation mode and validation context from its static context, as described in 3.7.1.5 Type of a Constructed Element. If the name of the constructed element is specified by a constant QName, this QName is added to the validation context for nested expressions. On the other hand, if the name of the constructed element is specified by a name expression, the validation context for nested expressions is set to global.

A computed element constructor might be used to make a modified copy of an existing element. For example, if the variable $e is bound to an element with numeric content, the following constructor might be used to create a new element with the same name and attributes as $e and with numeric content equal to twice the value of $e:

element
   {node-name($e)}
   {$e/@*, 2 * data($e)}

In this example, if $e is bound by the expression let $e := <length units="inches">{5}</length>, then the result of the example expression is the element <length units="inches">10</length>.

One important purpose of computed constructors is to allow the name of a node to be computed. We will illustrate this feature by an expression that translates the name of an element from one language to another. Suppose that the variable $dict is bound to a sequence of entries in a translation dictionary. Here is an example entry:

<entry word="address">
   <variant lang="German">Adresse</variant>
   <variant lang="Italian">indirizzo</variant>
</entry> 

Suppose further that the variable $e is bound to the following element:

<address>123 Roosevelt Ave. Flushing, NY 11368</address>

Then the following expression generates a new element in which the name of $e has been translated into Italian and the content of $e (including its attributes, if any) has been preserved. The first enclosed expression after the element keyword generates the name of the element, and the second enclosed expression generates the content and attributes:

  element 
    {$dict/entry[word=name($e)]/variant[lang="Italian"]}
    {$e/node()}

The result of this expression is as follows:

<indirizzo>123 Roosevelt Ave. Flushing, NY 11368</indirizzo>

Additional examples of computed element constructors can be found in E.4 Recursive Transformations.

Editorial note  
The namespace nodes to be generated in conjunction with the new element node have not yet been defined.
3.7.2.2 Computed Attribute Constructors

The name expression of a computed attribute constructor is processed as follows:

  1. If the name expression returns an expanded QName, that QName is used as the name of the constructed attribute.

  2. If the name expression returns a string, that string is cast to a QName and the resulting expanded QName is used as the name of the constructed attribute. If the cast fails, a dynamic error is raised.

  3. If the name expression does not return a QName or a string, a dynamic error is raised.

The content expression of a computed attribute constructor is processed as follows:

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.

  2. If the result of atomization is an empty sequence, the value of the attribute is the zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string, as an instance of xs:untypedAtomic, is the value of the attribute.

A computed attribute constructor does not perform any automatic validation of the constructed attribute. However, if the computed attribute constructor is inside an element constructor, the attribute will be validated during validation of its parent element.

  • Example:

    attribute size {4 + 3}
    

    The value of the size attribute is "7".

  • Example:

    attribute
       { if $sex = "M" then "husband" else "wife" }
       { <a>Hello</a>, 1 to 3, <b>Goodbye</b> }
    

    The name of the constructed attribute is either husband or wife. Its value is "Hello 1 2 3 Goodbye".

An attribute generated by a computed attribute constructor must not be a namespace declaration attribute--that is, its name must not be xmlns or a QName with prefix xmlns.

3.7.2.3 Document Node Constructors

All document node constructors are computed constructors. The result of a document node constructor is a new document node, with its own node identity.

A document node constructor is useful when the result of a query is to be a document in its own right. The following example illustrates a query that returns an XML document containing a root element named author-list:

document
   {
      <author-list>
         doc("bib.xml")//book/author
      </author-list>
   }

The content expression of a document node constructor is processed as follows:

  1. For each node returned by the content expression, a new deep copy of the node is constructed, including its children, attributes, and namespace nodes (if any). Each copied node has a new node identity. Copied element nodes are given the type annotation xs:anyType, and copied attribute nodes are given the type annotation xs:anySimpleType. For each adjacent sequence of one or more atomic values returned by the content expression, a new text node is constructed, containing the result of casting each atomic value to a string, with a single blank character inserted between adjacent values. The resulting sequence of nodes is called the content sequence.

  2. If the content sequence contains a document or attribute node, a type error is raised.

  3. The resulting sequence of nodes becomes the children of the new document node.

No schema validation is performed on the constructed document. The [XML] rules that govern the structure of an XML document (for example, the document node must have exactly one child that is an element node) are not enforced by the XQuery document node constructor.

3.7.2.4 Text Node Constructors

All text node constructors are computed constructors. The result of a text node constructor is a new text node, with its own node identity.

The content expression of a text node constructor is processed as follows:

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.

  2. If the result of atomization is an empty sequence, no text node is constructed. Otherwise, each atomic value in the atomized sequence is cast into a string.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string becomes the content of the constructed text node.

3.7.3 Other Constructors and Comments

The syntax for a CDATA section constructor, a processing instruction constructor, or an XML comment constructor is based on the syntax of the equivalent XML construct.

[100]    CdataSection    ::=    "<![CDATA[" Char* "]]>" /* ws: significant */
[101]    XmlProcessingInstruction    ::=    "<?" PITarget Char* "?>" /* ws: explicit */
[102]    XmlComment    ::=    "<!--" Char* "-->" /* ws: significant */

Each of the above constructors is terminated by the first occurrence of its ending delimiter. In other words, the content of a CDATA section may not contain the string "]]>", the content of a processing instruction may not contain the string "?>", and the content of an XML comment may not contain the string "-->".

The following examples illustrate constructors for processing instructions, comments, and CDATA sections.

<?format role="output" ?>
<!-- Tags are ignored in the following section -->
<![CDATA[ 
    <address>123 Roosevelt Ave. Flushing, NY 11368</address>
]]>

A CDATA section constructor constructs a text node whose content is the same as the content of the constructor. When this text node becomes a child of an element node, it is merged with adjacent text nodes in the normal way. A CDATA section constructor may be useful because it removes the need to escape special characters such as "<" and "&" within the scope of the CDATA section.

An implementation may choose to serialize text that was constructed using a CDATA section constructor by means of a CDATA section in the serialized output, but it is not obliged to do so. The fact that a CDATA section was used to construct the text is not visible in the Data Model.

Note that an XML comment actually constructs an XML comment node. An XQuery comment (see 3.1.5 XQuery Comments) is simply a comment used in documenting a query, and is not evaluated. Consider the following example.

(: This is an XQuery comment :)
<!-- This is an XML comment -->

The result of evaluating the above expression is as follows.

<!-- This is an XML comment -->

3.8 FLWOR Expressions

XQuery provides a feature called a FLWOR expression that supports iteration and binding of variables to intermediate results. This kind of expression is often useful for computing joins between two or more documents and for restructuring data. The name FLWOR, pronounced "flower", is suggested by the keywords for, let, where, order by, and return.

[41]    FLWORExpr    ::=    (ForClause | LetClause)+ WhereClause? OrderByClause? "return" ExprSingle
[42]    ForClause    ::=    "for" "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle ("," "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle)*
[44]    LetClause    ::=    "let" "$" VarName TypeDeclaration? ":=" ExprSingle ("," "$" VarName TypeDeclaration? ":=" ExprSingle)*
[115]    TypeDeclaration    ::=    "as" SequenceType
[43]    PositionalVar    ::=    "at" "$" VarName
[45]    WhereClause    ::=    "where" Expr
[46]    OrderByClause    ::=    ("order" "by" | "stable" "order" "by") OrderSpecList
[47]    OrderSpecList    ::=    OrderSpec ("," OrderSpec)*
[48]    OrderSpec    ::=    ExprSingle OrderModifier
[49]    OrderModifier    ::=    ("ascending" | "descending")? ("empty" "greatest" | "empty" "least")? ("collation" StringLiteral)?

The for and let clauses in a FLWOR expression generate a sequence of tuples of bound variables, called the tuple stream. The where clause serves to filter the tuple stream, retaining some tuples and discarding others. The order by clause imposes an ordering on the tuple stream. The return clause constructs the result of the FLWOR expression. The return clause is evaluated once for every tuple in the tuple stream, after filtering by the where clause, using the variable bindings in the respective tuples. The result of the FLWOR expression is an ordered sequence containing the concatenated results of these evaluations.

The following example of a FLWOR expression includes all of the possible clauses. The for clause iterates over all the departments in an input document, binding the variable $d to each department number in turn. For each binding of $d, the let clause binds variable $e to all the employees in the given department, selected from another input document. The result of the for and let clauses is a tuple stream in which each tuple contains a pair of bindings for $d and $e ($d is bound to a department number and $e is bound to a set of employees in that department). The where clause filters the tuple stream by keeping only those binding-pairs that represent departments having at least ten employees. The order by clause orders the surviving tuples in descending order by the average salary of the employees in the department. The return clause constructs a new big-dept element for each surviving tuple, containing the department number, headcount, and average salary.

for $d in doc("depts.xml")//deptno
let $e := doc("emps.xml")//emp[deptno = $d]
where count($e) >= 10
order by avg($e/salary) descending
return
   <big-dept>
      {
      $d,
      <headcount>{count($e)}</headcount>,
      <avgsal>{avg($e/salary)}</avgsal>
      }
   </big-dept>

The clauses in a FLWOR expression are described in more detail below.

3.8.1 For and Let Clauses

The purpose of the for and let clauses in a FLWOR expression is to produce a tuple stream in which each tuple consists of one or more bound variables.

The simplest example of a for clause contains one variable and an associated expression. It evaluates the expression and iterates over the items in the resulting sequence, binding the variable to each item in turn.

A for clause may also contain multiple variables, each with an associated expression. In this case, the for clause iterates each variable over the items that result from evaluating its expression. The resulting tuple stream contains one tuple for each combination of values in the Cartesian product of the sequences resulting from evaluating the given expressions. The order of the tuples in the tuple stream is determined by the order of the given expressions, as illustrated in the examples below.

A let clause may also contain one or more variables, each with an associated expression. Unlike a for clause, however, a let clause binds each variable to the result of its associated expression, without iteration. The variable bindings generated by let clauses are added to the binding tuples generated by the for clauses. If there are no for clauses, the let clauses generate one tuple containing all the variable bindings.

Although for and let clauses both bind variables, the manner in which variables are bound is quite different, as illustrated by the following examples. The first example uses a let clause:

let $s := (<one/>, <two/>, <three/>)
return <out>{$s}</out>

The variable $s is bound to the result of the expression (<one/>, <two/>, <three/>). Since there are no for clauses, the let clause generates one tuple that contains the binding of $s. The return clause is invoked for this tuple, creating the following output:

<out>
   <one/>
   <two/>
   <three/>
</out>

The next example is a similar query that contains a for clause instead of a let clause:

for $s in (<one/>, <two/>, <three/>)
return <out>{$s}</out>

In this example, the variable $s iterates over the given expression; first it is bound to <one/>, then to <two/>, and finally to <three/>. One tuple is generated for each of these bindings, and the return clause is invoked for each tuple, creating the following output:

<out>
   <one/>
</out>
<out>
   <two/>
</out>
<out>
   <three/>
</out>

The following example illustrates how binding tuples are generated by a for clause that contains multiple variables. Note that the order of the tuple stream is determined primarily by the order of the sequence bound to the leftmost variable, and secondarily by sequences bound to other variables, working from left to right.

for $i in (1, 2), $j in (3, 4)

The tuple stream generated by the above for clause is as follows (the order is significant):

($i = 1, $j = 3)
($i = 1, $j = 4)
($i = 2, $j = 3)
($i = 2, $j = 4)

The scope of a variable bound in a for or let clause comprises all subexpressions of the containing FLWOR expression that appear after the variable binding. The scope does not include the expression to which the variable is bound. The following example illustrates how for and let clauses may reference variables that were bound in earlier clauses in the same FLWOR expression:

for $x in input()
let $y := f($x)
for $z in g($x, $y)
return h($x, $y, $z)

Each variable bound in a for or let clause may have an optional type declaration, which is a type declared using the syntax in 2.4.3 SequenceType. If the type of a value bound to the variable does not match the declared type according to the rules for SequenceType Matching, a type error is raised. For example, the following expression raises a type error because the variable $salary has a type declaration that is not satisfied by the value that is bound to the variable:

let $salary as xs:decimal :=  "cat"
return $salary * 2

Each variable bound in a for clause may have an associated positional variable that is bound at the same time. The name of the positional variable is preceded by the keyword at. The positional variable always has an implied type of xs:integer. As a variable iterates over the items in a sequence, its positional variable iterates over the ordinal numbers of these items, starting with 1. Positional variables are illustrated by the following for clause:

for $car at $i in ("Ford", "Chevy"),
$pet at $j in ("Cat", "Dog")

The tuple stream generated by the above for clause is as follows (the order is significant):

($i = 1, $car = "Ford", $j = 1, $pet = "Cat")
($i = 1, $car = "Ford", $j = 2, $pet = "Dog")
($i = 2, $car = "Chevy", $j = 1, $pet = "Cat")
($i = 2, $car = "Chevy", $j = 2, $pet = "Dog")

3.8.2 Where Clause

The optional where clause serves as a filter for the tuples of variable bindings generated by the for and let clauses. The expression in the where clause, called the where-expression, is evaluated once for each of these tuples. If the effective boolean value of the where-expression is true, the tuple is retained and its variable bindings are used in an execution of the return clause. If the effective boolean value of the where-expression is false, the tuple is discarded. The effective boolean value of an expression is defined in 2.4.4.2 Effective Boolean Value.

The following expression illustrates how a where clause might be applied to a positional variable in order to perform sampling on an input sequence. This expression approximates the average value in a sequence by sampling one value out of each one hundred input values.

avg(for $x at $i in input() 
    where $i mod 100 = 0   
    return $x)

3.8.3 Order By and Return Clauses

The return clause of a FLWOR expression is evaluated once for each tuple in the tuple stream, and the results of these evaluations are concatenated to form the result of the FLWOR expression. If no order by clause is present, the order of the tuple stream is determined by the orderings of the sequences returned by the expressions in the for clauses. If an order by clause is present, it determines the order of the tuple stream. The order of the tuple stream, in turn, determines the order in which the return clause is evaluated using the variable bindings in the respective tuples.

An order by clause contains one or more ordering specifications, called orderspecs, as shown in the grammar above. For each tuple in the tuple stream, the orderspecs are evaluated, using the variable bindings in that tuple. The relative order of two tuples is determined by comparing the values of their orderspecs, working from left to right until a pair of unequal values is encountered. If the values to be compared are strings, the orderspec may indicate the collation to be used (if no collation is specified, the default collation is used.)

The process of evaluating and comparing the orderspecs is based on the following rules:

  • Atomization is applied to the result of the expression in each orderspec. If the result of atomization is neither a single atomic value nor an empty sequence, a type error is raised.

  • If the value of an orderspec has the dynamic type xdt:untypedAtomic (such as character data in a schemaless document), it is cast to the type xs:string.

  • Each orderspec must return values of the same type for all tuples in the tuple stream, and this type must be a (possibly optional) atomic type for which the gt operator is defined--otherwise, a dynamic error is raised.

When two orderspec values are compared to determine their relative position in the ordering sequence, the greater-than relationship is defined as follows:

  • When the orderspec specifies empty least, a value W is considered to be greater than a value V if one of the following is true:

    • V is an empty sequence and W is not an empty sequence.

    • V is NaN, and W is neither NaN nor an empty sequence.

    • No collation is specified, and W gt V is true.

    • A specific collation C is specified, and fn:compare(V, W, C) is less than zero.

  • When the orderspec specifies empty greatest, a value W is considered to be greater than a value V if one of the following is true:

    • W is an empty sequence and V is not an empty sequence.

    • W is NaN, and V is neither NaN nor an empty sequence.

    • No collation is specified, and W gt V is true.

    • A specific collation C is specified, and fn:compare(V, W, C) is less than zero.

  • When the orderspec specifies neither empty least nor empty greatest, it is implementation-defined whether the rules for empty least or empty greatest are used.

If T1 and T2 are two tuples in the tuple stream, and V1 and V2 are the first pair of values encountered when evaluating their orderspecs from left to right for which one value is greater than the other (as defined above), then:

  1. If V1 is greater than V2: If the orderspec specifies descending, then T1 precedes T2 in the tuple stream; otherwise, T2 precedes T1 in the tuple stream.

  2. If V2 is greater than V1: If the orderspec specifies descending, then T2 precedes T1 in the tuple stream; otherwise, T1 precedes T2 in the tuple stream.

If neither V1 nor V2 is greater than the other for any pair of orderspecs for tuples T1 and T2, then:

  1. If stable is specified, the original order of T1 and T2 is preserved in the tuple stream.

  2. If stable is not specified, the order of T1 and T2 in the tuple stream is implementation-defined.

An order by clause makes it easy to sort the result of a FLWOR expression, even if the sort key is not included in the result of the expression. For example, the following expression returns employee names in descending order by salary, without returning the actual salaries:

for $e in input() order by $e/salary return $e/name

The order by clause is the only facility provided by XQuery for specifying an order other than document order. Therefore, every query in which an order other than document order is required must contain a FLWOR expression, even though iteration would not otherwise be necessary. For example, a list of books with price less than 100 might be obtained by a simple path expression such as input()//book[price < 100]. But if these books are to be returned in alphabetic order by title, the query must be expressed as follows:

for $b in input()//book[price < 100]
order by $b/title
return $b

The following example illustrates an order by clause that uses several options. It causes a collection of books to be sorted in primary order by title, and in secondary descending order by price. A specific collation is specified for the title ordering, and in the ordering by price, books with no price are specified to occur last (as though they have the least possible price). Whenever two books with the same title and price occur, the keyword stable indicates that their input order is preserved.

for $b in input()//book
stable order by $b/title collation "eng-us",
   $b/price descending empty least
return $b

3.8.4 Example

The following example illustrates how FLWOR expressions can be nested, and how ordering can be specified at multiple levels of an element hierarchy. The example query inverts a document hierarchy to transform a bibliography into an author list. The input bibliography is a list of books in which each book contains a list of authors. The example is based on the following input:

<bib>
  <book>
    <title>TCP/IP Illustrated</title>
    <author>Stevens</author>
    <publisher>Addison-Wesley</publisher>
  </book>
  <book>
    <title>Advanced Unix Programming</title>
    <author>Stevens</author>
    <publisher>Addison-Wesley</publisher>
  </book>
  <book>
    <title>Data on the Web</title>
    <author>Abiteboul</author>
    <author>Buneman</author>
    <author>Suciu</author>
  </book>
</bib>

The following query transforms the input document into a list in which each author's name appears only once, followed by a list of titles of books written by that author. The distinct-values function is used to eliminate duplicates (by value) from a list of author nodes. The author list, and the lists of books published by each author, are returned in alphabetic order using the default collation.

<authlist>
 {
   for $a in distinct-values(input()//author)
   order by $a
   return
     <author>
        <name>
          { $a/text() }
        </name>
        <books>
          {
            for $b in input()//book[author = $a]
            order by $b/title
            return $b/title 
          }
        </books>
     </author>
 }
</authlist>

The result of the above expression is as follows:

<authlist>
   <author>
      <name>Abiteboul</name>
      <books>
         <title>Data on the Web</title>
      </books>
   </author>
   <author>
      <name>Buneman</name>
      <books>
         <title>Data on the Web</title>
      </books>
   </author>
   <author>
      <name>Stevens</name>
      <books>
         <title>TCP/IP Illustrated</title>
         <title>Advanced Unix Programming</title>
      </books>
   </author>
   <author>
      <name>Suciu</name>
      <books>
         <title>Data on the Web</title>
      </books>
   </author>
</authlist>

3.9 Unordered Expressions

In general, XQuery expressions return sequences that have a well-defined order. For example, the result of an axis step in a path expression is always returned in document order. Similarly, the result of a FLWOR expression is ordered by its order by clause and/or the expressions in its for clauses. However, in some expressions, the order of the result may not be significant to the user. In such an expression, one ordering may be much more efficient to materialize than another, and a significant performance advantage may be realized by allowing the system to materialize the results of the expression in the order it finds most efficient. XQuery provides a function named unordered for this purpose.

The unordered function takes any sequence of items as its argument, and returns the same sequence of items in a nondeterministic order. A call to the unordered function may be thought of as giving permission for the argument expression to be materialized in whatever order the system finds most efficient. The unordered function may be applied to the result of a query or to a subexpression inside a query.

The use of the unordered function is illustrated by the following example, which joins together two documents named parts.xml and suppliers.xml. The example returns the part numbers of red parts, paired with the supplier numbers of suppliers who supply these parts. If the unordered function were not used, the resulting list of (part number, supplier number) pairs would be required to have an ordering that is controlled primarily by the document order of parts.xml and secondarily by the document order of suppliers.xml. However, this might not be the most efficient way to process the query if the ordering of the result is not important. An XQuery implementation might be able to process the query more efficiently by using an index to find the red parts, or by using suppliers.xml rather than parts.xml to control the primary ordering of the result. The unordered keyword gives the query evaluator freedom to make these kinds of optimizations.

unordered(
  for $p in doc("parts.xml")//part[color = "Red"],
      $s in doc("suppliers.xml")//supplier
  where $p/suppno = $s/suppno  
  return
    <ps>
       { $p/partno, $s/suppno }
    </ps>
)

3.10 Conditional Expressions

XQuery supports a conditional expression based on the keywords if, then, and else.

Conditional Expression
[53]    IfExpr    ::=    "if" "(" Expr ")" "then" Expr "else" ExprSingle

The expression following the if keyword is called the test expression, and the expressions following the then and else keywords are called the then-expression and else-expression, respectively.

The first step in processing a conditional expression is to find the effective boolean value of the test expression, as defined in 2.4.4.2 Effective Boolean Value.

The value of a conditional expression is defined as follows: If the effective boolean value of the test expression is true, the value of the then-expression is returned. If the effective boolean value of the test expression is false, the value of the else-expression is returned.

Conditional expressions have a special rule for propagating dynamic errors. If the effective value of the test expression is true, the conditional expression ignores (does not raise) any dynamic errors encountered in the else-expression. In this case, since the else-expression can have no observable effect, it need not be evaluated. Similarly, if the effective value of the test expression is false, the conditional expression ignores any dynamic errors encountered in the then-expression, and the then-expression need not be evaluated.

Here are some examples of conditional expressions:

  • In this example, the test expression is a comparison expression:

    if ($widget1/unit-cost < $widget2/unit-cost) 
      then $widget1
      else $widget2
    
  • In this example, the test expression tests for the existence of an attribute named discounted, independently of its value:

    if ($part/@discounted) 
      then $part/wholesale 
      else $part/retail
    

3.11 Quantified Expressions

Quantified expressions support existential and universal quantification. The value of a quantified expression is always true or false.

[50]    QuantifiedExpr    ::=    ("some" "$" | "every" "$") VarName TypeDeclaration? "in" ExprSingle ("," "$" VarName TypeDeclaration? "in" ExprSingle)* "satisfies" ExprSingle

A quantified expression begins with a quantifier, which is the keyword some or every, followed by one or more in-clauses that are used to bind variables, followed by the keyword satisfies and a test expression. Each in-clause associates a variable with an expression that returns a sequence of values. The in-clauses generate tuples of variable bindings, using values drawn from the Cartesian product of the sequences returned by the binding expressions. Conceptually, the test expression is evaluated for each tuple of variable bindings. Results depend on the effective boolean values of the test expressions, as defined in 2.4.4.2 Effective Boolean Value. The value of the quantified expression is defined by the following rules:

  1. If the quantifier is some, the quantified expression is true if at least one evaluation of the test expression has the effective boolean value true; otherwise the quantified expression is false. This rule implies that, if the in-clauses generate zero binding tuples, the value of the quantified expression is false.

  2. If the quantifier is every, the quantified expression is true if every evaluation of the test expression has the effective boolean value true; otherwise the quantified expression is false. This rule implies that, if the in-clauses generate zero binding tuples, the value of the quantified expression is true.

The scope of a variable bound in a quantified expression comprises all subexpressions of the quantified expression that appear after the variable binding. The scope does not include the expression to which the variable is bound.

Each variable bound in an in-clause of a quantified expression may have an optional type declaration, which is a datatype declared using the syntax in 2.4.3 SequenceType. If the type of a value bound to the variable does not match the declared type according to the rules for SequenceType Matching, a type error is raised.

The order in which test expressions are evaluated for the various binding tuples is implementation-defined. If the quantifier is some, an implementation may return true as soon as it finds one binding tuple for which the test expression has an effective Boolean value of true, and it may raise a dynamic error as soon as it finds one binding tuple for which the test expression raises an error. Similarly, if the quantifier is every, an implementation may return false as soon as it finds one binding tuple for which the test expression has an effective Boolean value of false, and it may raise a dynamic error as soon as it finds one binding tuple for which the test expression raises an error. As a result of these rules, the value of a quantified expression is not deterministic in the presence of errors, as illustrated in the examples below.

Here are some examples of quantified expressions:

  • This expression is true if every part element has a discounted attribute (regardless of the values of these attributes):

    every $part in //part satisfies $part/@discounted
    
  • This expression is true if at least one employee element satisfies the given comparison expression:

    some $emp in //employee satisfies ($emp/bonus > 0.25 * $emp/salary)
    
  • In the following examples, each quantified expression evaluates its test expression over nine tuples of variable bindings, formed from the Cartesian product of the sequences (1, 2, 3) and (2, 3, 4). The expression beginning with some evaluates to true, and the expression beginning with every evaluates to false.

    some $x in (1, 2, 3), $y in (2, 3, 4) 
         satisfies $x + $y = 4
    
    every $x in (1, 2, 3), $y in (2, 3, 4) 
         satisfies $x + $y = 4
    
  • This quantified expression may either return true or raise a type error, since its test expression returns true for one variable binding and raises a type error for another:

    some $x in (1, 2, "cat") satisfies $x * 2 = 4
    
  • This quantified expression may either return false or raise a type error, since its test expression returns false for one variable binding and raises a type error for another:

    every $x in (1, 2, "cat") satisfies $x * 2 = 4
    
  • This quantified expression contains a type declaration that is not satisfied by every item in the test expression. If the Static Typing Feature is implemented, this expression raises a type error during the analysis phase. Otherwise, the expression may either return true or raise a type error during the evaluation phase.

    some $x as xs:integer in (1, 2, "cat") satisfies $x * 2 = 4
    

3.12 Expressions on SequenceTypes

In addition to their use in function parameters and results, SequenceTypes are used in instance of, typeswitch, cast, castable, and treat expressions.

3.12.1 Instance Of

[56]    InstanceofExpr    ::=    TreatExpr ( "instance" "of" SequenceType )?

The boolean operator instance of returns true if the value of its first operand matches the type named in its second operand, according to the rules for SequenceType Matching; otherwise it returns false. For example:

  • 5 instance of xs:integer

    This example returns true because the given value is an instance of the given type.

  • 5 instance of xs:decimal

    This example returns true because the given value is an integer literal, and xs:integer is derived by restriction from xs:decimal.

  • <a>{5}</a> instance of xs:integer

    This example returns false because the given value is not an integer; instead, it is an element containing an integer.

  • <a>{5}</a> instance of element(*, xs:integer)

    This example returns true if the validation process on the constructed element is successful and the schema definition for element a calls for content of type xs:integer.

  • . instance of element()

    This example returns true if the context item is an element node.

3.12.2 Typeswitch

[51]    TypeswitchExpr    ::=    "typeswitch" "(" Expr ")" CaseClause+ "default" ("$" VarName)? "return" ExprSingle
[52]    CaseClause    ::=    "case" ("$" VarName "as")? SequenceType "return" Expr

The typeswitch expression chooses one of several expressions to evaluate based on the dynamic type of an input value.

In a typeswitch expression, the typeswitch keyword is followed by an expression enclosed in parentheses, called the operand expression. This is the expression whose type is being tested. The remainder of the typeswitch expression consists of one or more case clauses and a default clause.

Each case clause specifies a SequenceType followed by a return expression. The effective case is the first case clause such that the value of the operand expression matches the SequenceType in the case clause, using the rules of SequenceType Matching. The value of the typeswitch expression is the value of the return expression in the effective case. If the value of the operand expression is not a value of any type named in a case clause, the value of the typeswitch expression is the value of the return expression in the default clause.

A case or default clause may optionally specify a variable name. Within the return expression of the case or default clause, this variable name is bound to the value of the operand expression, and its static type is considered to be the SequenceType named in the case or default clause. If the return expression does not depend on the value of the operand expression, the variable may be omitted from the case or default clause.

The scope of a variable binding in a case or default clause comprises that clause. It is not an error for more than one case or default clause in the same typeswitch expression to bind variables with the same name.

The following example shows how a typeswitch expression might be used to process an expression in a way that depends on its dynamic type.

typeswitch($customer/billing-address)
   case $a as element(*, USAddress) return $a/state
   case $a as element(*, CanadaAddress) return $a/province
   case $a as element(*, JapanAddress) return $a/prefecture
   default return "unknown"

3.12.3 Cast

[59]    CastExpr    ::=    ComparisonExpr ( "cast" "as" SingleType )?
[116]    SingleType    ::=    AtomicType "?"?

Occasionally it is necessary to convert a value to a specific datatype. For this purpose, XQuery provides a cast expression that creates a new value of a specific type based on an existing value. A cast expression takes two operands: an input expression and a target type. The type of the input expression is called the input type. The target type must be a named atomic type, represented by a QName, optionally followed by the occurrence indicator ? if an empty sequence is permitted. If the target type has no namespace prefix, it is considered to be in the default element namespace. The semantics of the cast expression are as follows:

  1. Atomization is performed on the input expression.

  2. If the result of atomization is a sequence of more than one atomic value, a type error is raised.

  3. If the result of atomization is an empty sequence:

    1. If ? is specified after the target type, the result of the cast expression is an empty sequence.

    2. If ? is not specified after the target type, a type error is raised.

  4. If the result of atomization is a single atomic value, the result of the cast expression depends on the input type and the target type. In general, the cast expression attempts to create a new value of the target type based on the input value. Only certain combinations of input type and target type are supported. The rules are listed below. For the purpose of these rules, we use the terms subtype and supertype in the following sense: if type B is derived from type A by restriction, then B is a subtype of A, and A is a supertype of B.

    1. cast is supported for the combinations of input type and target type listed in [XQuery 1.0 and XPath 2.0 Functions and Operators]. For each of these combinations, both the input type and the target type are built-in schema types. For example, a value of type xs:string can be cast into the type xs:decimal. For each of these built-in combinations, the semantics of casting are specified in [XQuery 1.0 and XPath 2.0 Functions and Operators].

    2. cast is supported if the input type is a derived atomic type and the target type is a supertype of the input type. In this case, the input value is mapped into the value space of the target type, unchanged except for its type. For example, if shoesize is derived by restriction from xs:integer, a value of type shoesize can be cast into the type xs:integer.

    3. cast is supported if the target type is a derived atomic type and the input type is xs:string or xdt:untypedAtomic. The input value is first converted to a value in the lexical space of the target type by applying the whitespace normalization rules for the target type; a dynamic error is raised if the resulting lexical value does not satisfy the pattern facet of the target type. The lexical value is then converted to the value space of the target type using the schema-defined rules for the target type; a dynamic error is raised if the resulting value does not satisfy all the facets of the target type.

    4. cast is supported if the target type is a derived atomic type and the input type is a supertype of the target type. The input value must satisfy all the facets of the target type (in the case of the pattern facet, this is checked by generating a string representation of the input value, using the rules for casting to xs:string). The resulting value is the same as the input value, but with a different dynamic type.

    5. If a primitive type P1 can be cast into a primitive type P2, then any subtype of P1 can be cast into any subtype of P2, provided that the facets of the target type are satisfied. First the input value is cast to P1 using rule (b) above. Next, the value of type P1 is cast to the type P2, using rule (a) above. Finally, the value of type P2 is cast to the target type, using rule (d) above.

    6. For any combination of input type and target type that is not in the above list, a cast expression raises a type error.

If casting from the input type to the target type is supported but nevertheless it is not possible to cast the input value into the value space of the target type, a dynamic error is raised. This includes the case when any facet of the target type is not satisfied. For example, the expression "2003-02-31" cast as xs:date would raise a dynamic error.

3.12.4 Castable

[58]    CastableExpr    ::=    CastExpr ( "castable" "as" SingleType )?

XQuery provides a form of Boolean expression that tests whether a given value is castable into a given target type. The expression V castable as T returns true if the value V can be successfully cast into the target type T by using a cast expression; otherwise it returns false. The castable predicate can be used to avoid errors at evaluation time. It can also be used to select an appropriate type for processing of a given value, as illustrated in the following example:

if ($x castable as hatsize)
then $x cast as hatsize
else if ($x castable as IQ)
then $x cast as IQ
else $x cast as xs:string

3.12.5 Constructor Functions

Constructor functions provide an alternative syntax for casting.

For every built-in atomic type T that is defined in [XML Schema], as well as the predefined types xdt:dayTimeDuration, xdt:yearMonthDuration, and xdt:untypedAtomic, a built-in constructor function is provided. The signature of the built-in constructor function for type T is as follows:

T($x as item) as T

The constructor function for type T accepts any single item (either a node or an atomic value) as input, and returns a value of type T (or raises a dynamic error). Its semantics are exactly the same as a cast expression with target type T. The built-in constructor functions are described in more detail in [XQuery 1.0 and XPath 2.0 Functions and Operators]. The following are examples of built-in constructor functions:

  • This example is equivalent to "2000-01-01" cast as xs:date.

    xs:date("2000-01-01")
    
  • This example is equivalent to ($floatvalue * 0.2E-5) cast as xs:decimal.

    xs:decimal($floatvalue * 0.2E-5)
    
  • This example returns a dayTimeDuration value equal to 21 days. It is equivalent to "P21D" cast as xdt:dayTimeDuration.

    xdt:dayTimeDuration("P21D")
    

For each user-defined top-level atomic type T in the in-scope type definitions, a constructor function is effectively defined. Like the built-in constructor functions, the constructor functions for user-defined types have the same name (including namespace or lack of namespace) as the type, accept any item as input, and have semantics identical to a cast expression with the user-defined type as target type. For example, if usa:zipcode is a user-defined top-level atomic type in the in-scope type definitions, then the expression usa:zipcode("12345") is equivalent to the expression "12345" cast as usa:zipcode.

If the argument to any constructor function is a literal value, the result of the function may be computed statically, and an error encountered in this process may be reported as a static error.

3.12.6 Treat

[57]    TreatExpr    ::=    CastableExpr ( "treat" "as" SequenceType )?

XQuery provides an expression called treat that can be used to modify the static type of its operand.

Like cast, the treat expression takes two operands: an expression and a SequenceType. Unlike cast, however, treat does not change the dynamic type or value of its operand. Instead, the purpose of treat is to ensure that an expression has an expected type at evaluation time.

The semantics of expr1 treat as type1 are as follows:

  • During static analysis (if the Static Typing Feature is implemented):

    type1 must be derived by restriction from the static type of expr1--otherwise, a type error is raised. The static type of the treat expression is type1. This enables the expression to be used as an argument of a function that requires a parameter of type1.

  • During expression evaluation (at "run-time"):

    If expr1 matches type1, using the SequenceType Matching rules in 2.4.3 SequenceType, the treat expression returns the value of expr1; otherwise, it raises a dynamic error. If the value of expr1 is returned, its identity is preserved. The treat expression ensures that the value of its expression operand conforms to the expected type at run-time.

  • Example:

    $myaddress treat as element(*, USAddress)
    

    The static type of $myaddress may be element(*, Address), a less specific type than element(*, USAddress). However, at run-time, the value of $myaddress must match the type element(*, USAddress) using SequenceType Matching rules; otherwise a dynamic error is raised.

3.13 Validate Expressions

[75]    ValidateExpr    ::=    ("validate" "{" | ("validate" "global" "{") | ("validate" "context" SchemaContextLocation "{") | ("validate" SchemaMode SchemaContext? "{")) Expr "}"
[12]    SchemaMode    ::=    "lax" | "strict" | "skip"
[76]    SchemaContext    ::=    ("context" SchemaContextLocation) | "global"
[129]    SchemaContextLocation    ::=    (SchemaContextPath QName) | SchemaGlobalTypeName
[128]    SchemaContextPath    ::=    SchemaGlobalContext "/" SchemaContextStep "/"*
[14]    SchemaGlobalContext    ::=    QName | SchemaGlobalTypeName
[13]    SchemaGlobalTypeName    ::=    "type" "(" QName ")"
[15]    SchemaContextStep    ::=    QName

A validate expression can be used to validate a document node or an element node with respect to the in-scope schema definitions, using the schema validation process described in [XML Schema]. If the argument of a validate expression does not evaluate to exactly one document or element node, a type error is raised.

In the result of the validate expression, the input node and all its descendant nodes are replaced by new nodes that have their own identity and contain type annotations and default values generated by the validation process. The hierarchical relationships among the input nodes are preserved among the nodes created by the validation process.

The result of a validate expression is equivalent to the following steps:

  1. The input node and its descendants are converted from the Data Model to an XML Information Set ([XML Infoset]), using the mapping described in [XQuery 1.0 and XPath 2.0 Data Model]. If the input node is a document node, the resulting Information Set must represent a well-formed XML document (for example, the document node must have exactly one child that is an element node); otherwise a type error is raised.

  2. The Information Set produced in the previous step is validated according to the rules in [XML Schema], using the in-scope schema definitions. If the topmost node is a document node, the validation process includes checking of uniqueness and reference constraints. If the topmost node is an element node, checks of uniqueness and reference constraints are omitted. The result of this step is a Post-Schema Validation Infoset (PSVI). If the validation process is not successful, a type error is raised.

  3. The PSVI produced in the previous step is converted back into the Data Model, using the mapping described in [XQuery 1.0 and XPath 2.0 Data Model].

A validate expression may specify a validation mode, which may have one of the following three values:

  • strict requires that each element to be validated must be present in the in-scope element declarations, and that the content of each element must conform to its definition.

  • skip indicates that no validation is to be attempted. In this mode, each element node is given the type annotation xs:anyType, and each attribute node is given the type annotation xdt:untypedAtomic.

  • lax behaves like strict for elements that are present in the in-scope element declarations, and like skip for elements that are not present.

If no validation mode is specified for a validate expression, the expression uses the validation mode in its static context. If a validation mode is specified, that validation mode is made effective in the static context for nested expressions.

A validate expression may also contain a validation context that affects the interpretation of element names. If the validation context is global, all top-level element names in the material to be validated are checked against top-level in-scope schema declarations. Alternatively, the validation context may specify that top-level element names in the validated material are to be interpreted as local names within a given schema context. In this case, the validation context begins with the name of a top-level element or type. The steps inside the validation context trace a path relative to this top-level element or type, as illustrated by the following examples, which are based on schemas defined in [XML Schema], Part 0:

  • Suppose that $x is bound to a shipTo element. Then validate strict context po:purchaseOrder {$x} validates the value of $x in strict mode, in the context of the top-level element declaration po:purchaseOrder.

  • Suppose that $y is bound to a productName element. Then validate context po:purchaseOrder/items/item {$y} validates the value of $y in the context of an item element, inside an items element, inside the top-level element declaration po:purchaseOrder.

  • Suppose that $z is bound to a zip element. Then validate context type(po:USAddress) {$z} validates the value of $z in the context of the top-level type declaration po:USAddress.

If no validation context is specified for a validate expression, the expression uses the validation context in its static context. If a validation context is specified, that validation context is made effective in the static context for nested expressions.

Since each element constructor automatically performs validation on the constructed element, it is rarely necessary to use an explicit validate expression. Typically, an explicit validate expression is used to enclose an element constructor if the user wishes to specify a validation mode or validation context that is different from that of the static context, thus affecting the behavior of the element constructor and its nested expressions. For example, the following expression constructs an element named zip and specifies that it must be validated in strict mode and in the context of the top-level type named po:Address:

validate strict context type(po:Address)
   { <zip>90952</zip> }

4 Modules and Prologs

[30]    Module    ::=    MainModule | LibraryModule
[31]    MainModule    ::=    Prolog QueryBody
[32]    LibraryModule    ::=    ModuleDecl Prolog
[33]    ModuleDecl    ::=    "module" StringLiteral
[34]    Prolog    ::=    Version? (NamespaceDecl
| XMLSpaceDecl
| DefaultNamespaceDecl
| DefaultCollationDecl
| SchemaImport
| ModuleImport
| VarDefn
| ValidationDecl)* FunctionDefn*
[38]    QueryBody    ::=    Expr

A module is a piece of XQuery code that can independently undergo the analysis phase described in 2.4.2 Type Checking. A module that contains a Prolog followed by a Query Body is called a main module. A query consists of exactly one main module. In a main module, the Query Body can be evaluated, and its value is the result of the query. A module that contains a Module Declaration followed by a Prolog is called a library module. A library module cannot be evaluated directly; instead, it provides function and variable definitions that can be imported into other modules. No module may contain both a Module Declaration and a Query Body.

The Module Declaration, if present, consists of the keyword module followed by a URI that serves as the target namespace of the module. The target namespace is the default namespace for variable definitions in the module, and is also the default function namespace for the module unless the module's Prolog explicitly declares a different default function namespace.

All variables and functions defined in a library module must be, explicitly or implicitly, in the target namespace of the library module. If a library module declares a default function namespace that is different from its target namespace (for example, in order to use the functions in [XQuery 1.0 and XPath 2.0 Functions and Operators] without a prefix), then the names of functions defined in the library module must have explicit prefixes that are bound to the target namespace of the library module.

Any module may import a library module by means of a module import that specifies the target namespace of the library module to be imported. When a module imports one or more library modules, the variables and functions defined in the imported modules are added to the static context and (where applicable) to the dynamic context of the importing module.

The Prolog is a series of declarations and definitions that create the environment for query processing. The Prolog may contain a version declaration that specifies the version of the XQuery language that is used in the module. The Prolog may also include namespace declarations, schema imports, module imports, variable definitions, and declarations that control various processing options. In addition, the Prolog may contain some function definitions.

The Query Body, if present, consists of an expression that defines the result of the query, as described in 3 Expressions. A module can be evaluated only if it has a Query Body.

4.1 Version Declaration

[35]    Version    ::=    "xquery" "version" StringLiteral

A version declaration specifies the applicable XQuery syntax and semantics for a module. The version number "1.0" indicates the requirement that the query must be processed by an XQuery Version 1.0 processor. If the version declaration is not present, the version is presumed to be "1.0". An XQuery implementation must raise a static error when processing a query labeled with a version that the implementation does not support. It is the intent of the XQuery working group to give later versions of this specification numbers other than "1.0", but this intent does not indicate a commitment to produce any future versions of XQuery, nor if any are produced, to use any particular numbering scheme.

The following is an example of a version declaration:

xquery version "1.0"

4.2 Namespace Declarations

[110]    NamespaceDecl    ::=    "declare" "namespace" NCName "=" StringLiteral

A Namespace Declaration defines a namespace prefix and associates it with a namespace URI, adding the (prefix, URI) pair to the set of in-scope namespaces. The string literal used in a namespace declaration must be a valid URI, and may not be a zero-length string. The namespace declaration is in scope throughout the query in which it is declared, unless it is overridden by a namespace declaration attribute in an element constructor.

The following query illustrates a namespace declaration:

declare namespace foo = "http://example.org"
<foo:bar> Lentils </foo:bar>

In the query result, the newly created node is in the namespace associated with the namespace URI http://example.org.

Multiple declarations of the same namespace prefix in the Prolog result in a static error. However, a declaration of a namespace in the Prolog can override a prefix that has been predeclared in the static context.

(: Error: multiple declarations of namespace 'xx' :)

declare namespace xx = "http://example.org/foo"
declare namespace xx = "http://example.org/bar"

<xx:bing/>

It is a static error to use a QName with a namespace prefix that has not been declared.

In an element constructor, a namespace declaration attribute can be used to bind a prefix to a namespace, adding a (prefix, URI) pair to the set of in-scope namespaces for the element in which it occurs and for nested expressions. The binding of a prefix by a namespace declaration attribute overrides any binding of the same prefix by a higher-level element or by the Prolog. The value of a namespace declaration attribute must be a valid URI. In the Data Model, a namespace declaration attribute generates a namespace node rather than an attribute node. Namespace nodes are not retrieved by queries that return the attributes of an element. The following query illustrates a namespace declaration attribute that binds the prefix foo within the scope of a constructed element:

<foo:bar xmlns:foo="http://example.org">{ //foo:bing }</foo:bar>

When element or attribute names are compared, they are considered identical if the local part and namespace URI match. Namespace prefixes need not be identical for two names to match, as illustrated by the following example:

declare namespace xx = "http://example.org"

let $i := <foo:bar xmlns:foo = "http://example.org">
              <foo:bing> Lentils </foo:bing>
          </foo:bar>
return $i/xx:bing

Although the namespace prefixes xx and foo differ, both are bound to the namespace URI "http://example.org". Since xx:bing and foo:bing have the same local name and the same namespace URI, they match. The output of the above query is as follows.

<foo:bing> Lentils </foo:bing>

XQuery has five predefined namespace prefixes that are present in the in-scope namespaces before each query is processed. These prefixes may be used without an explicit declaration. Their definitions may be overridden by namespace declarations in the Prolog or by namespace declaration attributes on constructed elements (except for the prefix xml, which may not be redefined.) The five predefined namespace prefixes are as follows:

  • xml = http://www.w3.org/XML/1998/namespace

  • xs = http://www.w3.org/2001/XMLSchema

  • xsi = http://www.w3.org/2001/XMLSchema-instance

  • fn = http://www.w3.org/2003/05/xpath-functions

  • xdt = http://www.w3.org/2003/05/xpath-datatypes

Additional predefined namespace prefixes may be added to the in-scope namespaces by an implementation.

The namespace prefix xmlns also has a special significance (it identifies a namespace declaration attribute), and it may not be redefined.

4.3 Default Namespace Declarations

[111]    DefaultNamespaceDecl    ::=    ("default" "element" | "default" "function") "namespace" "=" StringLiteral

Default Namespace Declarations can be used in a Prolog to facilitate the use of unprefixed QNames. The string literal used in a default namespace declaration must be a valid URI, and may be a zero-length string. The following kinds of default namespace declarations are supported:

  • Declaration of a default element namespace defines a namespace URI that is associated with unprefixed names of elements and types. If no default element namespace is declared, unqualified names of elements and types are in no namespace. The following example illustrates the declaration of a default namespace for elements and types:

    default element namespace = "http://example.org/names"
    

    If a direct element constructor includes an attribute named xmlns, it is considered to be a namespace declaration attribute that specifies a new default element namespace within the scope of the constructed element and its descendants. For example, within the scope of the following constructed element, the default element namespace is http://example.org/altnames.

    <abc xmlns="http://example.org/altnames">Content goes here.</abc>
    
  • A Prolog may contain a declaration for a default function namespace. If no default function namespace is declared in the Prolog of a library module, the default function namespace for that module is the target namespace of the module. If no default function namespace is declared in the Prolog of a main module, the default function namespace for that module is the namespace of XPath/XQuery functions, http://www.w3.org/2003/05/xpath-functions. The following example illustrates the declaration of a default function namespace:

    default function namespace = "http://example.com/functions"
    

    The effect of declaring a default function namespace is that all functions in the default function namespace, including implicitly-defined constructor functions, are aliased with a name that has the original local name, but no namespace URI. It is a static error if this results in two functions having the same name and arity. The function may be referred to using either its original name or its alias--that is, the namespace prefix becomes optional.

    When a function call uses a function name with no prefix, the local name of the function must match a function in one of the following categories:

    1. Functions (including implicitly-defined constructor functions) in the default function namespace.

    2. Functions defined in the Prolog of the current module or an imported module, without a namespace prefix.

    3. Constructor functions for atomic types in the in-scope type definitions whose names are in no namespace.



Unqualified attribute names and variable names are never in a namespace, with one exception: in a variable definition in a library module, if the name of the variable being defined has no prefix, it is considered to be in the target namespace of the library module.

4.4 Schema Imports

[135]    SchemaImport    ::=    "import" "schema" SchemaPrefix? StringLiteral "at" StringLiteral?
[136]    SchemaPrefix    ::=    ("namespace" NCName "=") | ("default" "element" "namespace" "=")

A schema import imports the element, attribute, and type definitions from a named schema into the in-scope schema definitions. The string literals in a schema import must be valid URIs. The schema import specifies the target namespace of the schema to be imported, and optionally the location of the schema. A schema import may also bind a namespace prefix to the target namespace of the imported schema, or may declare that target namespace to be the default element namespace. The optional location indication can be disregarded by an implementation if it has another way to locate the given schema.

The following example imports the schema for an XHTML document, specifying both its target namespace and its location, and binding the prefix xhtml to this namespace:

import schema namespace xhtml="http://www.w3.org/1999/xhtml" 
            at "http://example.org/xhtml/xhtml.xsd"

The following example imports a schema by specifying only its target namespace, and makes it the default element namespace for the query:

import schema default element namespace="http://example.org/abc"

It is a static error to import two schemas that both define the same name in the same symbol space and in the same scope. For instance, a query may not import two schemas that include top-level element declarations for two elements with the same expanded name.

Note:

XQuery 1.0 supports querying of DTD-validated documents only if the Static Typing Feature is not enabled. Since XQuery 1.0 does not provide a means for importing Document Type Definitions (DTDs), implementations supporting the Static Typing Feature level are not required to recognize or support type information in DTDs.

If static typing of queries that access DTD-validated documents is required, the DTD should be converted to an XML Schema and the resulting schema should be imported into the query. We request public comment on this restriction.

4.5 Module Imports

[36]    ModuleImport    ::=    "import" "module" ("namespace" NCName "=")? StringLiteral "at" StringLiteral?

A module import imports the function definitions and variable definitions from the Prolog of a library module into the in-scope functions and in-scope variables of the importing module. The string literals in a module import must be valid URIs. The module import identifies the module to be imported by its target namespace, and may also specify its location by using an at clause. Implementations may locate modules in any manner that is convenient, and are free to ignore the specified location if they have another way to find a module. By means of an optional namespace clause, a module import may bind a namespace prefix to the target namespace of the imported module.

Each module has its own static context. A module import imports only functions and variable definitions; it does not import other declarations from the imported module, such as in-scope schema definitions or in-scope namespaces. Module imports are not transitive--that is, importing a module provides access only to function and variable definitions contained directly in the imported module. For example, if module A imports module B, and module B imports module C, module A does not have access to the functions and variables defined in module C. Two modules may import each other.

It is a type error to import a module if the importing module's in-scope type definitions do not include definitions for the type names that appear in variable definitions, function parameters, or function returns found in the imported module. It is a static error to import a module that contains function definitions or variable definitions whose names are already defined in the static context of the importing module.

To illustrate the above rules, suppose that a certain schema defines a type named triangle. Suppose that a library module imports the schema, binds its target namespace to the prefix geo, and defines a function with the signature area($t as geo:triangle) as xs:double. If a query wishes to use this function, it must import both the library module and the schema on which it is based. Importing the library module alone would not provide access to the type definition on which the area function is defined.

4.6 Variable Definitions

[37]    VarDefn    ::=    "define" S "variable" "$" VarName TypeDeclaration? (("{" Expr "}") | "external")
[20]    VarName    ::=    QName
[115]    TypeDeclaration    ::=    "as" SequenceType

A variable definition adds the static type of a variable to the static context, and may also add a value for the variable to the evaluation context.

If a variable definition includes a type, that type is added to the static context as the type of the variable. If a variable definition includes an expression but not an explicit type, the static type of the variable is inferred from the static type of the expression. If a variable definition includes both a type and an expression, the static type of the expression must be compatible with the declared static type; otherwise a type error is raised.

If a variable definition includes an expression, the value of the expression is bound to the variable in the evaluation context. If the variable definition includes the keyword external, a value must be provided for the variable by the external environment before the query can be evaluated. If the value provided by the external environment is not compatible with the declared type of the variable, a type error is raised.

If a variable definition contains neither a type nor an expression, the type and value of the variable must both be provided by the external environment at evaluation time. The static type of such a variable is considered to be xs:anyType.

A variable or function may appear in the expression part of a variable definition only if that variable or function is defined before the variable definition (that is, its definition must be declared or imported earlier in the Prolog than the variable definition in which it is used.)

All variables defined in a library module must be implicitly or explicitly in the target namespace of the library module. When a library module is imported, variables in the imported module are added to the in-scope variables of the importing module.

The term variable definition always refers to a definition of a variable in a Prolog. The binding of a variable to a value in a query expression, such as a FLWOR expression, is known as a variable binding, and does not make the variable visible to an importing module.

Here are some examples of variable definitions:

  • The following definition specifies both the type and the value of a variable. This definition causes the type xs:integer to be associated with variable $x in the static context, and the value 7 to be associated with variable $x in the evaluation context.

    define variable $x as xs:integer {7}
    
  • The following definition specifies a value but not a type. The static type of the variable is inferred from the static type of its value. In this case, the variable $x has a static type of xs:decimal, inferred from its value which is 7.5.

    define variable $x {7.5}
    
  • The following definition specifies a type but not a value. The keyword external indicates that the value of the variable will be provided by the external environment. At evaluation time, if the variable $x in the evaluation context does not have a value of type xs:integer, a type error is raised.

    define variable $x as xs:integer external
    
  • The following definition specifies neither a type nor a value. It simply declares that the query depends on the existence of a variable named $x, whose type and value will be provided by the external environment. During query analysis, the type of $x is considered to be xs:anyType. During query evaluation, the evaluation context must include a type and a value for $x, and its value must be compatible with its type.

    define variable $x external
    

4.7 Validation Declaration

[134]    ValidationDecl    ::=    "validation" "lax" | "validation" "strict" | "validation" "skip"

The validation declaration in the Prolog sets the validation mode in the static context to strict, lax, or skip. This establishes a default validation mode for the query. The default validation context for the query is always set to global. The default validation mode and validation context can be overridden by validate expressions within the body of the query. The significance of validation mode and validation context are described in 3.13 Validate Expressions.

4.8 Xmlspace Declaration

[108]    XMLSpaceDecl    ::=    "declare" "xmlspace" "=" ("preserve" | "strip")

The xmlspace declaration in a Prolog controls whether boundary whitespace is preserved by element and attribute constructors during execution of the query, as described in 3.7.1.4 Whitespace in Element Content. If xmlspace = preserve is specified, boundary whitespace is preserved. If xmlspace = strip is specified or if no xmlspace declaration is present, boundary whitespace is stripped (deleted).

The following example illustrates an xmlspace declaration:

declare xmlspace = preserve

4.9 Default Collation

[109]    DefaultCollationDecl    ::=    "default" "collation" "=" StringLiteral

A Prolog may declare a default collation, which is the name of the collation to be used by all functions and operators that require a collation if no other collation is specified. For example, the gt operator on strings is defined by a call to the fn:compare function, which takes an optional collation parameter. Since the gt operator does not specify a collation, the fn:compare function implements gt by using the default collation specified in the Prolog. The default collation is identified by a literal string containing a URI.

The following example illustrates a declaration of a default collation:

default collation = "http://example.org/languages/Icelandic"

If a Prolog specifies no default collation, the system provided default collation is chosen. If the system does not provide a default collation, the Unicode codepoint collation (http://www.w3.org/2003/05/xpath-functions/collation/codepoint) is used. If a Prolog specifies more than one default collation, or value specified does not identify a collation known to the implementation, a static error is raised.

4.10 Function Definitions

In addition to the built-in functions described in [XQuery 1.0 and XPath 2.0 Functions and Operators], XQuery allows users to define functions of their own. A function definition specifies the name of the function, the names and datatypes of the parameters, and the datatype of the result. All datatypes are specified using the syntax described in 2.4.3 SequenceType. A function definition also includes either an expression called the function body that defines how the result of the function is computed from its parameters, or the keyword external, indicating that the function is an external function.

[112]    FunctionDefn    ::=    "define" "function" QName "(" ParamList? (")" | (")" "as" SequenceType)) (EnclosedExpr | "external") /* pn: parens */
[113]    ParamList    ::=    Param ("," Param)*
[114]    Param    ::=    "$" VarName TypeDeclaration?
[115]    TypeDeclaration    ::=    "as" SequenceType

External functions are implemented outside the query environment. For example, an XQuery implementation might provide a set of external functions in addition to the core function library described in [XQuery 1.0 and XPath 2.0 Functions and Operators]. The purpose of a function definition for an external function is to declare the datatypes of the function parameters and result, for use in type checking of the query that contains or imports the function declaration.

An XQuery implementation may provide a facility whereby external functions can be implemented using a host programming language, but it is not required to do so. If such a facility is provided, the protocols by which parameters are passed to an external function, and the result of the function is returned to the invoking query, are implementation-defined. An XQuery implementation may augment the type system of [XQuery 1.0 and XPath 2.0 Data Model] with additional types that are designed to facilitate exchange of data with host programming languages, or it may provide mechanisms for the user to define such types. For example, a type might be provided that encapsulates an object returned by an external function, such as an SQL database connection.

The name of a function may be qualified with a namespace prefix. If no namespace prefix is specified, the function is in no namespace. To avoid the risk of name collisions, authors of general-purpose or long-lived function libraries are encouraged to define their functions in an explicit namespace.

If a function parameter is declared using a name but no type, its default type is item*. If the returns clause is omitted from a function definition, its default return type is item*.

The parameters of a function definition are considered to be variables whose scope is the function body. It is an error for a function definition to have more than one parameter with the same name. The type of a function parameter can be any type that can be expressed as a SequenceType (see 2.4.3 SequenceType).

The following example illustrates the definition and use of a function that accepts a sequence of valid employee elements (as defined in the in-scope element declarations), summarizes them by department, and returns a sequence of valid dept elements (again, as defined in the in-scope element declarations).

  • Using a function, prepare a summary of employees that are located in Denver.

    define function summary($emps as element(employee)*) 
       as element(dept)*
    {
       for $d in distinct-values($emps/deptno)
       let $e := $emps[deptno = $d]
       return
          <dept>
             <deptno>{$d}</deptno>
             <headcount> {count($e)} </headcount>
             <payroll> {sum($e/salary)} </payroll>
          </dept>
    }
    
    summary(doc("acme_corp.xml")//employee[location = "Denver"])
    

Rules for converting function arguments to their declared parameter types, and for converting the result of a function to its declared result type, are described in 3.1.4 Function Calls

A function may be defined recursively--that is, it may reference its own definition. Mutually recursive functions, whose bodies reference each other, are also allowed. The following example defines a recursive function that computes the maximum depth of a node hierarchy, and calls the function to find the maximum depth of a particular document. In its definition, the user-defined function depth calls the built-in functions empty and max.

  • Find the maximum depth of the document named partlist.xml.

    define function depth($e as node()) as xs:integer
    {
       (: A node with no children has depth 1 :)
       (: Otherwise, add 1 to max depth of children :)
       if (empty($e/*)) then 1
       else max(for $c in $e/* return depth($c)) + 1
    }
    
    depth(doc("partlist.xml"))
    

In XQuery 1.0, user-defined functions may not be overloaded. Only one function definition may have a given name. However, some of the built-in functions in the XQuery core library are overloaded--for example, the fn:string function can be called with either zero arguments or one argument.

Since a constructor function is effectively defined for every user-defined atomic type in the in-scope type definitions, a static error is raised if the Prolog attempts to define a function with the same name as any of these types.

Note:

If a future version of XQuery supports overloading of user-defined functions, an ambiguity may arise between a function that takes a node as parameter and a function with the same name that takes an atomic value as parameter (since a function call automatically extracts the atomic value of a node when necessary). The designers of such a future version of XQuery can avoid this ambiguity by writing suitable rules to govern function overloading. Nevertheless, users who are concerned about this possibility may choose to explicitly extract atomic values from nodes when calling functions that expect atomic values.

A XQuery Grammar

A.1 EBNF

The following grammar uses the same Basic Extended Backus-Naur Form (EBNF) notation as [XML], except that grammar symbols always have initial capital letters. The notation "< ... >" is used to indicate a grouping of terminals that together may help disambiguate the individual symbols. To help readability, this "< ... >" notation is absent in the EBNF in the main body of this document.

Comments on grammar productions are between '/*' and '*/' symbols. A 'pn:' prefix means a 'Parser Note', and are meant as clarifications for parsing rules, and are explained in A.1.1 Parsing Notes. A 'ws:' prefix explains the whitespace rules for the production, the details of which are explained in A.2.1 Whitespace Rules

Note:

The Semicolon character is reserved for future use.

Named Terminals
[1]    Pragma    ::=    "(::" "pragma" QName PragmaContents* "::)" /* pn: parens */
[2]    MustUnderstandExtension    ::=    "(::" "extension" QName ExtensionContents* "::)" /* pn: parens */
[3]    ExprComment    ::=    "(:" (ExprCommentContent | ExprComment)* ":)" /* pn: parens */
[4]    ExprCommentContent    ::=    Char
[5]    PragmaContents    ::=    Char
[6]    ExtensionContents    ::=    Char
[7]    IntegerLiteral    ::=    Digits
[8]    DecimalLiteral    ::=    ("." Digits) | (Digits "." [0-9]*) /* ws: explicit */
[9]    DoubleLiteral    ::=    (("." Digits) | (Digits ("." [0-9]*)?)) ("e" | "E") ("+" | "-")? Digits /* ws: explicit */
[10]    StringLiteral    ::=    ('"' (PredefinedEntityRef | CharRef | ('"' '"') | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | ("'" "'") | [^'&])* "'") /* ws: significant */
[11]    S    ::=    [http://www.w3.org/TR/REC-xml#NT-S]
[12]    SchemaMode    ::=    "lax" | "strict" | "skip"
[13]    SchemaGlobalTypeName    ::=    "type" "(" QName ")"
[14]    SchemaGlobalContext    ::=    QName | SchemaGlobalTypeName
[15]    SchemaContextStep    ::=    QName
[16]    Digits    ::=    [0-9]+
[17]    EscapeQuot    ::=    '"' '"'
[18]    PITarget    ::=    NCName
[19]    NCName    ::=    [http://www.w3.org/TR/REC-xml-names/#NT-NCName]
[20]    VarName    ::=    QName
[21]    QName    ::=    [http://www.w3.org/TR/REC-xml-names/#NT-QName]
[22]    PredefinedEntityRef    ::=    "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";" /* ws: explicit */
[23]    HexDigits    ::=    [0-9] | [a-f] | [A-F]+
[24]    CharRef    ::=    "&#" (Digits | ("x" HexDigits)) ";" /* ws: explicit */
[25]    EscapeApos    ::=    "''"
[26]    Char    ::=    [http://www.w3.org/TR/REC-xml#NT-Char]
[27]    ElementContentChar    ::=    Char - [{}<&]
[28]    QuoteAttributeContentChar    ::=    Char - ["{}<&]
[29]    AposAttributeContentChar    ::=    Char - ['{}<&]
Non-Terminals
[30]    Module    ::=    MainModule | LibraryModule
[31]    MainModule    ::=    Prolog QueryBody
[32]    LibraryModule    ::=    ModuleDecl Prolog
[33]    ModuleDecl    ::=    <"module" StringLiteral>
[34]    Prolog    ::=    Version? (NamespaceDecl
| XMLSpaceDecl
| DefaultNamespaceDecl
| DefaultCollationDecl
| SchemaImport
| ModuleImport
| VarDefn
| ValidationDecl)* FunctionDefn*
[35]    Version    ::=    <"xquery" "version" StringLiteral>
[36]    ModuleImport    ::=    <"import" "module"> ("namespace" NCName "=")? StringLiteral <"at" StringLiteral>?
[37]    VarDefn    ::=    <"define" S "variable" "$"> VarName TypeDeclaration? (("{" Expr "}") | "external")
[38]    QueryBody    ::=    Expr
[39]    Expr    ::=    ExprSingle ("," ExprSingle)*
[40]    ExprSingle    ::=    FLWORExpr
| QuantifiedExpr
| TypeswitchExpr
| IfExpr
| OrExpr
[41]    FLWORExpr    ::=    (ForClause | LetClause)+ WhereClause? OrderByClause? "return" ExprSingle
[42]    ForClause    ::=    <"for" "$"> VarName TypeDeclaration? PositionalVar? "in" ExprSingle ("," "$" VarName TypeDeclaration? PositionalVar? "in" ExprSingle)*
[43]    PositionalVar    ::=    "at" "$" VarName
[44]    LetClause    ::=    <"let" "$"> VarName TypeDeclaration? ":=" ExprSingle ("," "$" VarName TypeDeclaration? ":=" ExprSingle)*
[45]    WhereClause    ::=    "where" Expr
[46]    OrderByClause    ::=    (<"order" "by"> | <"stable" "order" "by">) OrderSpecList
[47]    OrderSpecList    ::=    OrderSpec ("," OrderSpec)*
[48]    OrderSpec    ::=    ExprSingle OrderModifier
[49]    OrderModifier    ::=    ("ascending" | "descending")? (<"empty" "greatest"> | <"empty" "least">)? ("collation" StringLiteral)?
[50]    QuantifiedExpr    ::=    (<"some" "$"> | <"every" "$">) VarName TypeDeclaration? "in" ExprSingle ("," "$" VarName TypeDeclaration? "in" ExprSingle)* "satisfies" ExprSingle
[51]    TypeswitchExpr    ::=    <"typeswitch" "("> Expr ")" CaseClause+ "default" ("$" VarName)? "return" ExprSingle
[52]    CaseClause    ::=    "case" ("$" VarName "as")? SequenceType "return" Expr
[53]    IfExpr    ::=    <"if" "("> Expr ")" "then" Expr "else" ExprSingle
[54]    OrExpr    ::=    AndExpr ( "or" AndExpr )*
[55]    AndExpr    ::=    InstanceofExpr ( "and" InstanceofExpr )*
[56]    InstanceofExpr    ::=    TreatExpr ( <"instance" "of"> SequenceType )?
[57]    TreatExpr    ::=    CastableExpr ( <"treat" "as"> SequenceType )?
[58]    CastableExpr    ::=    CastExpr ( <"castable" "as"> SingleType )?
[59]    CastExpr    ::=    ComparisonExpr ( <"cast" "as"> SingleType )?
[60]    ComparisonExpr    ::=    RangeExpr ( (ValueComp
| GeneralComp
| NodeComp
| OrderComp) RangeExpr )?
[61]    RangeExpr    ::=    AdditiveExpr ( "to" AdditiveExpr )?
[62]    AdditiveExpr    ::=    MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )*
[63]    MultiplicativeExpr    ::=    UnaryExpr ( ("*" | "div" | "idiv" | "mod") UnaryExpr )*
[64]    UnaryExpr    ::=    ("-" | "+")* UnionExpr
[65]    UnionExpr    ::=    IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )*
[66]    IntersectExceptExpr    ::=    ValueExpr ( ("intersect" | "except") ValueExpr )*
[67]    ValueExpr    ::=    ValidateExpr | PathExpr
[68]    PathExpr    ::=    ("/" RelativePathExpr?)
| ("//" RelativePathExpr)
| RelativePathExpr
[69]    RelativePathExpr    ::=    StepExpr (("/" | "//") StepExpr)*
[70]    StepExpr    ::=    AxisStep | FilterStep
[71]    AxisStep    ::=    (ForwardStep | ReverseStep) Predicates
[72]    FilterStep    ::=    PrimaryExpr Predicates
[73]    PrimaryExpr    ::=    Literal | FunctionCall | ("$" VarName) | ParenthesizedExpr | Constructor
[74]    Predicates    ::=    ("[" Expr "]")*
[75]    ValidateExpr    ::=    (<"validate" "{"> | (<"validate" "global"> "{") | (<"validate" "context"> SchemaContextLocation "{") | (<"validate" SchemaMode> SchemaContext? "{")) Expr "}"
[76]    SchemaContext    ::=    ("context" SchemaContextLocation) | "global"
[77]    Constructor    ::=    ElementConstructor
| XmlComment
| XmlProcessingInstruction
| CdataSection
| ComputedDocumentConstructor
| ComputedElementConstructor
| ComputedAttributeConstructor
| ComputedTextConstructor
[78]    GeneralComp    ::=    "=" | "!=" | "<" | "<=" | ">" | ">="
[79]    ValueComp    ::=    "eq" | "ne" | "lt" | "le" | "gt" | "ge"
[80]    NodeComp    ::=    "is" | "isnot"
[81]    OrderComp    ::=    "<<" | ">>"
[82]    ForwardStep    ::=    (ForwardAxis NodeTest) | AbbreviatedForwardStep
[83]    ReverseStep    ::=    (ReverseAxis NodeTest) | AbbreviatedReverseStep
[84]    AbbreviatedForwardStep    ::=    "." | ("@" NameTest) | NodeTest
[85]    AbbreviatedReverseStep    ::=    ".."
[86]    ForwardAxis    ::=    <"child" "::">
| <"descendant" "::">
| <"attribute" "::">
| <"self" "::">
| <"descendant-or-self" "::">
[87]    ReverseAxis    ::=    <"parent" "::">
[88]    NodeTest    ::=    KindTest | NameTest
[89]    NameTest    ::=    QName | Wildcard
[90]    Wildcard    ::=    "*"
| <NCName ":" "*">
| <"*" ":" NCName>
/* ws: explicit */
[91]    Literal    ::=    NumericLiteral | StringLiteral
[92]    NumericLiteral    ::=    IntegerLiteral | DecimalLiteral | DoubleLiteral
[93]    ParenthesizedExpr    ::=    "(" Expr? ")"
[94]    FunctionCall    ::=    <QName "("> (ExprSingle ("," ExprSingle)*)? ")"
[95]    ElementConstructor    ::=    "<" QName AttributeList ("/>" | (">" ElementContent* "</" QName S? ">")) /* ws: explicit */
/* pn: lt */
[96]    ComputedDocumentConstructor    ::=    <"document" "{"> Expr "}"
[97]    ComputedElementConstructor    ::=    (<"element" QName "{"> | (<"element" "{"> Expr "}" "{")) Expr? "}"
[98]    ComputedAttributeConstructor    ::=    (<"attribute" QName "{"> | (<"attribute" "{"> Expr "}" "{")) Expr? "}"
[99]    ComputedTextConstructor    ::=    <"text" "{"> Expr? "}"
[100]    CdataSection    ::=    "<![CDATA[" Char* "]]>" /* ws: significant */
[101]    XmlProcessingInstruction    ::=    "<?" PITarget Char* "?>" /* ws: explicit */
[102]    XmlComment    ::=    "<!--" Char* "-->" /* ws: significant */
[103]    ElementContent    ::=    ElementContentChar
| "{{"
| "}}"
| ElementConstructor
| EnclosedExpr
| CdataSection
| CharRef
| PredefinedEntityRef
| XmlComment
| XmlProcessingInstruction
/* ws: significant */
[104]    AttributeList    ::=    (S (QName S? "=" S? AttributeValue)?)* /* ws: explicit */
[105]    AttributeValue    ::=    ('"' (EscapeQuot | AttributeValueContent)* '"')
| ("'" (EscapeApos | AttributeValueContent)* "'")
/* ws: significant */
[106]    AttributeValueContent    ::=    QuoteAttributeContentChar
| AposAttributeContentChar
| CharRef
| "{{"
| "}}"
| EnclosedExpr
| PredefinedEntityRef
/* ws: significant */
[107]    EnclosedExpr    ::=    "{" Expr "}"
[108]    XMLSpaceDecl    ::=    <"declare" "xmlspace"> "=" ("preserve" | "strip")
[109]    DefaultCollationDecl    ::=    <"default" "collation" "="> StringLiteral
[110]    NamespaceDecl    ::=    <"declare" "namespace"> NCName "=" StringLiteral
[111]    DefaultNamespaceDecl    ::=    (<"default" "element"> | <"default" "function">) "namespace" "=" StringLiteral
[112]    FunctionDefn    ::=    <"define" "function"> <QName "("> ParamList? (")" | (<")" "as"> SequenceType)) (EnclosedExpr | "external") /* pn: parens */
[113]    ParamList    ::=    Param ("," Param)*
[114]    Param    ::=    "$" VarName TypeDeclaration?
[115]    TypeDeclaration    ::=    "as" SequenceType
[116]    SingleType    ::=    AtomicType "?"?
[117]    SequenceType    ::=    (ItemType OccurrenceIndicator?)
| <"empty" "(" ")">
[118]    AtomicType    ::=    QName
[119]    ItemType    ::=    AtomicType | KindTest | <"item" "(" ")">
[120]    KindTest    ::=    DocumentTest
| ElementTest
| AttributeTest
| ProcessingInstructionTest
| CommentTest
| TextTest
| AnyKindTest
[121]    ElementTest    ::=    <"element" "("> ((SchemaContextPath LocalName)
| (NodeName ("," TypeName "nillable"?)?))? ")"
[122]    AttributeTest    ::=    <"attribute" "("> ((SchemaContextPath "@" LocalName)
| ("@" NodeName ("," TypeName)?))? ")"
[123]    ProcessingInstructionTest    ::=    <"processing-instruction" "("> StringLiteral? ")"
[124]    DocumentTest    ::=    <"document-node" "("> ElementTest? ")"
[125]    CommentTest    ::=    <"comment" "("> ")"
[126]    TextTest    ::=    <"text" "("> ")"
[127]    AnyKindTest    ::=    <"node" "("> ")"
[128]    SchemaContextPath    ::=    <SchemaGlobalContext "/"> <SchemaContextStep "/">*
[129]    SchemaContextLocation    ::=    (SchemaContextPath QName) | SchemaGlobalTypeName
[130]    LocalName    ::=    QName
[131]    NodeName    ::=    QName | "*"
[132]    TypeName    ::=    QName | "*"
[133]    OccurrenceIndicator    ::=    "?" | "*" | "+"
[134]    ValidationDecl    ::=    <"validation" "lax"> | <"validation" "strict"> | <"validation" "skip">
[135]    SchemaImport    ::=    <"import" "schema"> SchemaPrefix? StringLiteral <"at" StringLiteral>?
[136]    SchemaPrefix    ::=    ("namespace" NCName "=") | (<"default" "element"> "namespace" "=")

A.1.1 Parsing Notes

  1. A look-ahead of one character is required to distinguish function patterns from a QName followed by a comment. For example:address (: this may be empty :) may be mistaken for a call to a function named "address" unless this lookahead is employed.

  2. Token disambiguation of the overloaded "<" pattern is defined in terms of positional lexical states. The "<" comparison operator can not occur in the same places as a "<" tag open pattern. The "<" comparison operator can only occur in the OPERATOR state, and the "<" tag open pattern can only occur in the DEFAULT and the ELEMENT_CONTENT states. (These states are only a specification tool, and do not imply an implementation strategy for this same effect.)

A.2 Lexical structure

Legal characters are those allowed in the [XML] recommendation.

When patterns are simple string matches, the strings are embedded directly into the EBNF. In other cases, named terminals are used.

It is up to an implementation to decide on the exact tokenization strategy, which may be different depending on the parser construction. In the EBNF, the notation "< ... >" is used to indicate a grouping of terminals that together may help disambiguate the individual symbols.

This document uses lexical states to assist with terminal symbol recognition. The states specify lexical constraints and transitions based on grammatical positioning. The rules for calculating these states are given in the A.2.2 Lexical Rules section. The specification of these states in this document does not imply any tokenization strategy on the part of implementations.

When tokenizing, the longest possible match that is valid in the current lexical state is prefered .

All keywords are case sensitive.

A.2.1 Whitespace Rules

For readability, Whitespace may be used in most expressions even though not explicitly notated in the EBNF. Whitespace may be freely added between terminals, except a few cases where whitespace is needed to disambiguate the token. For instance, in XML, "-" is a valid character in an element or attribute name. When used as an operator after the characters of a name, it must be separated from the name, e.g. by using whitespace or parentheses.

Special whitespace notation is specified with the EBNF productions, when it is different from the default rules, as follows.

Whitespace: explicit

"ws: explicit" means that the EBNF notation must explicitly notate where whitespace is allowed, otherwise whitespace may not be freely used.

Whitespace: significant

"ws: significant" means that whitespace is significant as value content.

For XQuery, Whitespace is not freely allowed in the non-computed Constructor productions, but is specified explicitly in the grammar, in order to be more consistent with XML. The lexical states where whitespace must have explicit specification are as follows: START_TAG, END_TAG, ELEMENT_CONTENT, XML_COMMENT, PROCESSING_INSTRUCTION, PROCESSING_INSTRUCTION_CONTENT, CDATA_SECTION, QUOT_ATTRIBUTE_CONTENT, and APOS_ATTRIBUTE_CONTENT.

A.2.2 Lexical Rules

Editorial note  
The role of these states as normative parts of the specification is being investigated. One proposal suggests that only of subset of these states need be normative.

The lexical contexts and transitions between lexical contexts is described in terms of a series of states and transitions between those states.

The tables below define the complete lexical rules for XQuery. Each table corresponds to a lexical state in which the tokens listed are recognized only in that state. When a given token is recognized in the given state, the transition to the next state is given. In some cases, a transition will "push" the current state or a specific state onto an abstract stack, and will later restore that state by a "pop" when another lexical event occurs.

The lexical states have in many cases close connection to the parser productions. However, just because a token is recognized in a certain lexical state, does not mean it will be legal in the parser state.

The DEFAULT State

This state is for patterns that occur at the beginning of an expression or subexpression.

Pattern Transition To State
DecimalLiteral, "..", ".", DoubleLiteral, IntegerLiteral, <NCName ":" "*">, <"stable" "order" "by">, "]", ")", <"*" ":" NCName>, "*", StringLiteral, <"typeswitch" "(">
OPERATOR
<"default" "collation" "=">, <"declare" "namespace">
NAMESPACEDECL
<"default" "element">, <"default" "function">, <"import" "schema">, <"import" "module">
NAMESPACEKEYWORD
"$", <"for" "$">, <"let" "$">, <"some" "$">, <"every" "$">
VARNAME
<"define" S "variable" "$">
VARNAME
pushState(DEFAULT)
<")" "as">
ITEMTYPE
<"element" "(">, <"attribute" "(">, <"comment" "(">, <"text" "(">, <"node" "(">, <"processing-instruction" "(">, <"document-node" "(">
KINDTEST
pushState(OPERATOR)
OfType
QNAME
"<!--"
XML_COMMENT
pushState()
"<?"
PROCESSING_INSTRUCTION
pushState()
"<![CDATA["
CDATA_SECTION
pushState()
"<"
START_TAG
pushState(OPERATOR)
<"declare" "xmlspace">
XMLSPACE_DECL
"}"
popState()
<"validate" "{">, <"validate" "global">
DEFAULT
pushState(OPERATOR)
<"validate" "context">, <"validate" SchemaMode>
KINDTEST
pushState(OPERATOR)
<"element" "{">, <"attribute" "{">
pushState(OPERATOR);pushState(DEFAULT)
<"attribute" QName "{">, <"element" QName "{">, <"document" "{">, <"text" "{">
pushState(OPERATOR)
<"define" "function">
DEFAULT
pushState(DEFAULT)
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()
"{", <"xquery" "version" StringLiteral>, <"at" StringLiteral>, "@", <"attribute" "::">, <"child" "::">, <"descendant-or-self" "::">, <"descendant" "::">, <"parent" "::">, <"self" "::">, ",", <"if" "(">, "[", "(", "-", "+", QMark, <QName "(">, <"validation" "lax">, <"validation" "strict">, <"validation" "skip">, <"module" StringLiteral>, "//", "/"
(maintain state)


The OPERATOR State

This state is for patterns that are defined for operators.

Pattern Transition To State
<"define" "function">
DEFAULT
pushState(DEFAULT)
"external", "and", <"at" StringLiteral>, "at", ":=", ",", "div", "else", "=", "except", "eq", "ge", "gt", "le", "lt", "ne", ">=", ">>", ">", "idiv", "global", "intersect", "in", "isnot", "is", "[", "(", "<=", "<<", "<", "-", "mod", "*", "!=", <"order" "by">, "or", "+", QMark, "return", "satisfies", "//", "/", "then", "to", "union", "|", "where", "{"
DEFAULT
<"validate" "{">
DEFAULT
pushState(OPERATOR)
<"default" "collation" "=">
NAMESPACEDECL
<"import" "schema">, <"import" "module">, <"default" "element">, <"default" "function">
NAMESPACEKEYWORD
<"declare" "namespace">
NAMESPACEDECL
<"instance" "of">, <"castable" "as">, <"cast" "as">, <"treat" "as">, "case", "as", <")" "as">, InContext
ITEMTYPE
OfType
QNAME
<"declare" "xmlspace">
XMLSPACE_DECL
"}"
popState()
"$", <"for" "$">, <"let" "$">, <"some" "$">, <"every" "$">
VARNAME
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()
"]", IntegerLiteral, DecimalLiteral, DoubleLiteral, <"typeswitch" "(">, <"stable" "order" "by">, "collation", ")", "ascending", "descending", <"empty" "greatest">, <"empty" "least">, StringLiteral, "default", <NCName ":" "*">, <"*" ":" NCName>, ".", ".."
(maintain state)


The QNAME State

When a qualified name is expected, and it is required to remove ambiguity from patterns that look like functions, this state is used.

Pattern Transition To State
<NCName ":" "*">, <"*" ":" NCName>, ".", ".."
OPERATOR
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()


The NAMESPACEDECL State

This state occurs inside of a namespace declaration, and is needed to recognize a NCName that is to be used as the prefix, as opposed to allowing a QName to occur. (Otherwise, the difference between NCName and QName are ambiguous.)

Pattern Transition To State
StringLiteral
DEFAULT
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()
"=", NCName
(maintain state)


The NAMESPACEKEYWORD State

This state occurs at places where the keyword "namespace" is expected, which would otherwise be ambiguous compared to a QName. QNames can not occur in this state.

Pattern Transition To State
StringLiteral, <"at" StringLiteral>
DEFAULT
"namespace"
NAMESPACEDECL
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()
<"default" "element">, <"default" "function">
(maintain state)


The XMLSPACE_DECL State

This state occurs at places where the keywords "preserve" and "strip" is expected to support "declare xmlspace". QNames can not occur in this state.

Pattern Transition To State
"preserve", "strip"
DEFAULT
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()
"="
(maintain state)


The ITEMTYPE State

This state distinguishes tokens that can occur only inside the ItemType production.

Pattern Transition To State
"$"
VARNAME
<"empty" "(" ")">
OPERATOR
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()
<"element" "(">, <"attribute" "(">, <"comment" "(">, <"text" "(">, <"node" "(">, <"processing-instruction" "(">, <"document-node" "(">
KINDTEST
pushState(OCCURRENCEINDICATOR)
QName, <"item" "(" ")">
OCCURRENCEINDICATOR


The KINDTEST State
Pattern Transition To State
"{"
DEFAULT
<SchemaGlobalContext "/">, SchemaGlobalTypeName
SCHEMACONTEXTSTEP
")"
popState()
"*", QName
CLOSEKINDTEST
"@", "context", "global", StringLiteral
(maintain state)


The CLOSEKINDTEST State
Pattern Transition To State
")"
popState()
","
KINDTEST
"{"
DEFAULT
"nillable"
(maintain state)


The OCCURRENCEINDICATOR State
Pattern Transition To State
NotOccurrenceIndicator
OPERATOR
input_stream.backup(1)
"?", "*", "+"
OPERATOR


The SCHEMACONTEXTSTEP State

This state distinguishes the SchemaContextStep from the SchemaGlobalContext.

Pattern Transition To State
<SchemaContextStep "/">, "@"
(maintain state)
"{"
DEFAULT
QName
CLOSEKINDTEST


The VARNAME State

This state differentiates variable names from qualified names. This allows only the pattern of a QName to be recognized when otherwise ambiguities could occur.

Pattern Transition To State
VarName
OPERATOR
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()


The START_TAG State

This state allows attributes in the native XML syntax, and marks the beginning of an element construction. Element constructors also push the current state, popping it at the conclusion of an end tag. In the START_TAG state, the string ">" is recognized as a token which is associated with the transition to the original state.

Pattern Transition To State
"/>"
popState()
">"
ELEMENT_CONTENT
'"'
QUOT_ATTRIBUTE_CONTENT
"'"
APOS_ATTRIBUTE_CONTENT
"{"
DEFAULT
pushState()
QName, "="
(maintain state)


The ELEMENT_CONTENT State

This state allows XML-like content, without these characters being misinterpreted as expressions. The character "{" marks a transition to the DEFAULT state, i.e. the start of an embedded expression, and the "}" character pops back to the ELEMENT_CONTENT state. To allow curly braces to be used as character content, a double left or right curly brace is interpreted as a single curly brace character. The string "</" is interpreted as the beginning of an end tag, which is associated with a transition to the END_TAG state.

Pattern Transition To State
"</"
END_TAG
"{"
DEFAULT
pushState()
"<!--"
XML_COMMENT
pushState()
"<?"
PROCESSING_INSTRUCTION
pushState()
"<![CDATA["
CDATA_SECTION
pushState()
"<"
START_TAG
pushState()
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()
PredefinedEntityRef, CharRef, "{{", "}}", ElementContentChar
(maintain state)


The END_TAG State

When the end tag is terminated, the state is popped to the state that was pushed at the start of the corresponding start tag.

Pattern Transition To State
">"
popState()
"{"
DEFAULT
pushState()
QName
(maintain state)


The XML_COMMENT State

The "<--" token marks the beginning of an XML Comment, and the "-->" token marks the end. This allows no special interpretation of other characters in this state.

Pattern Transition To State
"-->"
popState()
Char, PragmaContents, ExtensionContents
(maintain state)


The EXPR_COMMENT State

The "(:" token marks the beginning of an expression Comment, and the ":)" token marks the end. This allows no special interpretation of other characters in this state.

Pattern Transition To State
":)", "::)"
popState()
"(:"
EXPR_COMMENT
pushState()
"(::"
EXT_KEY
pushState()
ExprCommentContent
(maintain state)


The EXT_KEY State

The "(::" token marks the beginning of an expression extension, which must be followed by a keyword.

Pattern Transition To State
QName, QName
EXPR_COMMENT
"pragma", "extension"
(maintain state)


The PROCESSING_INSTRUCTION State

In this state, only lexemes that are legal in a processing instruction name are recognized.

Pattern Transition To State
PITarget
PROCESSING_INSTRUCTION_CONTENT


The PROCESSING_INSTRUCTION_CONTENT State

In this state, only characters are that are legal in processing instruction content are recognized.

Pattern Transition To State
"?>"
popState()
Char
(maintain state)


The CDATA_SECTION State

In this state, only lexemes that are legal in a CDATA section are recognized.

Pattern Transition To State
"]]>"
popState()
Char
(maintain state)


The QUOT_ATTRIBUTE_CONTENT State

This state allows content legal for attributes. The character "{" marks a transition to the DEFAULT state, i.e. the start of an embedded expression, and the "}" character pops back to the original state. To allow curly braces to be used as character content, a double left or right curly brace is interpreted as a single curly brace character. This state is the same as QUOT_ATTRIBUTE_CONTENT, except that apostrophes are allowed without escaping, and an unescaped quote marks the end of the state.

Pattern Transition To State
'"'
START_TAG
"{"
DEFAULT
pushState()
EscapeQuot, PredefinedEntityRef, CharRef, "{{", "}}", QuoteAttributeContentChar
(maintain state)


The APOS_ATTRIBUTE_CONTENT State

This state is the same as QUOT_ATTRIBUTE_CONTENT, except that quotes are allowed, and an unescaped apostrophe marks the end of the state.

Pattern Transition To State
"'"
START_TAG
"{"
DEFAULT
pushState()
EscapeApos, PredefinedEntityRef, CharRef, "{{", "}}", AposAttributeContentChar
(maintain state)


A.3 Reserved Function Names

The following is a list of names that may not be used as user function names, in an unprefixed form.

  • if

  • typeswitch

  • node

  • comment

  • text

  • processing-instruction

A.4 Precedence Order

In all cases the grammar defines built-in precedence. In the cases where a number of statements are a choice at the same production level, the expressions are always evaluated from left to right.

B Type Promotion and Operator Mapping

B.1 Type Promotion

Under certain circumstances, an atomic value can be promoted from one type to another. Type promotion is used in function calls (see 3.1.4 Function Calls) and in processing of operators that accept numeric operands (listed in the tables below). The following type promotions are permitted:

  1. A value of type xs:float (or any type derived by restriction from xs:float) can be promoted to the type xs:double. The result is the xs:double value that is the same as the original value. This kind of promotion may cause loss of precision.

  2. A value of type xs:decimal (or any type derived by restriction from xs:decimal) can be promoted to either of the types xs:float or xs:double. The result is the value of the target type that is closest to the original value.

Note that promotion is different from subtype substitution. For example:

  • A function that expects a parameter $p of type xs:float can be invoked with a value of type xs:decimal. This is an example of promotion. The value is actually converted to the expected type. Within the body of the function, $p instance of xs:decimal returns false.

  • A function that expects a parameter $p of type xs:decimal can be invoked with a value of type xs:integer. This is an example of subtype substitution. The value retains its original type. Within the body of the function, $p instance of xs:integer returns true.

B.2 Operator Mapping

The tables in this section list the combinations of types for which the various operators of XQuery are defined. For each valid combination of types, the table indicates the function(s) that are used to implement the operator and the type of the result. Definitions of the functions can be found in [XQuery 1.0 and XPath 2.0 Functions and Operators]. Note that in some cases the function does not implement the full semantics of the given operator. For a complete description of each operator (including its behavior for empty sequences or sequences of length greater than one), see the descriptive material in the main part of this document.

Operators listed in the tables may be validly applied to operands whose types are derived by restriction from the listed operand types. For example, a table entry indicates that the gt operator may be applied to two xs:date operands, returning xs:boolean. Therefore, the gt operator may also be applied to two (possibly different) subtypes of xs:date, also returning xs:boolean.

In the operator tables, the term numeric refers to the types xs:integer, xs:decimal, xs:float, and xs:double. An operator whose operands and result are designated as numeric might be thought of as representing four operators, one for each of the numeric types. For example, the numeric + operator might be thought of as representing the following four operators:

Operator First operand type Second operand type Result type
+ xs:integer xs:integer xs:integer
+ xs:decimal xs:decimal xs:decimal
+ xs:float xs:float xs:float
+ xs:double xs:double xs:double

A numeric operator accepts operands of the four numeric types and any type that is derived by restriction from one of the four numeric types. If the result type of an operator is listed as numeric, it means "the first numeric type, in promotion order, into which all operands can be converted by subtype substitution and promotion." As an example, suppose that the type hatsize is derived from xs:integer and the type shoesize is derived from xs:float. Then if the + operator is invoked with operands of type hatsize and shoesize, it returns a result of type xs:float. Similarly, if + is invoked with two operands of type hatsize it returns a result of type xs:integer.

In the following tables, the term Gregorian refers to the types xs:gYearMonth, xs:gYear, xs:gMonthDay, xs:gDay, and xs:gMonth. For binary operators that accept two Gregorian-type operands, both operands must have the same type (for example, if one operand is of type xs:gDay, the other operand must be of type xs:gDay.)

Binary Operators
Operator Type(A) Type(B) Function Result type
A + B numeric numeric op:numeric-add(A, B) numeric
A + B xs:date xdt:yearMonthDuration op:add-yearMonthDuration-to-date(A, B) xs:date
A + B xdt:yearMonthDuration xs:date op:add-yearMonthDuration-to-date(B, A) xs:date
A + B xs:date xdt:dayTimeDuration op:add-dayTimeDuration-to-date(A, B) xs:date
A + B xdt:dayTimeDuration xs:date op:add-dayTimeDuration-to-date(B, A) xs:date
A + B xs:time xdt:dayTimeDuration op:add-dayTimeDuration-to-time(A, B) xs:time
A + B xdt:dayTimeDuration xs:time op:add-dayTimeDuration-to-time(B, A) xs:time
A + B xs:datetime xdt:yearMonthDuration op:add-yearMonthDuration-to-dateTime(A, B) xs:dateTime
A + B xdt:yearMonthDuration xs:datetime op:add-yearMonthDuration-to-dateTime(B, A) xs:dateTime
A + B xs:datetime xdt:dayTimeDuration op:add-dayTimeDuration-to-dateTime(A, B) xs:dateTime
A + B xdt:dayTimeDuration xs:datetime op:add-dayTimeDuration-to-dateTime(B, A) xs:dateTime
A + B xdt:yearMonthDuration xdt:yearMonthDuration op:add-yearMonthDurations(A, B) xdt:yearMonthDuration
A + B xdt:dayTimeDuration xdt:dayTimeDuration op:add-dayTimeDurations(A, B) xdt:dayTimeDuration
A - B numeric numeric op:numeric-subtract(A, B) numeric
A - B xs:date xs:date op:subtract-dates(A, B) xdt:dayTimeDuration
A - B xs:date xdt:yearMonthDuration op:subtract-yearMonthDuration-from-date(A, B) xs:date
A - B xs:date xdt:dayTimeDuration op:subtract-dayTimeDuration-from-date(A, B) xs:date
A - B xs:time xs:time op:subtract-times(A, B) xdt:dayTimeDuration
A - B xs:time xdt:dayTimeDuration op:subtract-dayTimeDuration-from-time(A, B) xs:time
A - B xs:datetime xs:datetime fn:subtract-dateTimes-yielding-dayTimeDuration(A, B) xdt:dayTimeDuration
A - B xs:datetime xdt:yearMonthDuration op:subtract-yearMonthDuration-from-dateTime(A, B) xs:dateTime
A - B xs:datetime xdt:dayTimeDuration op:subtract-dayTimeDuration-from-dateTime(A, B) xs:dateTime
A - B xdt:yearMonthDuration xdt:yearMonthDuration op:subtract-yearMonthDurations(A, B) xdt:yearMonthDuration
A - B xdt:dayTimeDuration xdt:dayTimeDuration op:subtract-dayTimeDurations(A, B) xdt:dayTimeDuration
A * B numeric numeric op:numeric-multiply(A, B) numeric
A * B xdt:yearMonthDuration xs:decimal op:multiply-yearMonthDuration(A, B) xdt:yearMonthDuration
A * B xs:decimal xdt:yearMonthDuration op:multiply-yearMonthDuration(B, A) xdt:yearMonthDuration
A * B xdt:dayTimeDuration xs:decimal op:multiply-dayTimeDuration(A, B) xdt:dayTimeDuration
A * B xs:decimal xdt:dayTimeDuration op:multiply-dayTimeDuration(B, A) xdt:dayTimeDuration
A idiv B xs:integer xs:integer op:integer-div(A, B) xs:integer
A div B numeric numeric op:numeric-divide(A, B) numeric; but xs:decimal if both operands are xs:integer
A div B xdt:yearMonthDuration xs:decimal op:divide-yearMonthDuration(A, B) xdt:yearMonthDuration
A div B xdt:dayTimeDuration xs:decimal op:divide-dayTimeDuration(A, B) xdt:dayTimeDuration
A mod B numeric numeric op:numeric-mod(A, B) numeric
A eq B numeric numeric op:numeric-equal(A, B) xs:boolean
A eq B xs:boolean xs:boolean op:boolean-equal(A, B) xs:boolean
A eq B xs:string xs:string op:numeric-equal(fn:compare(A, B), 1) xs:boolean
A eq B xs:date xs:date op:date-equal(A, B) xs:boolean
A eq B xs:time xs:time op:time-equal(A, B) xs:boolean
A eq B xs:dateTime xs:dateTime op:datetime-equal(A, B) xs:boolean
A eq B xdt:yearMonthDuration xdt:yearMonthDuration op:yearMonthDuration-equal(A, B) xs:boolean
A eq B xdt:dayTimeDuration xdt:dayTimeDuration op:dayTimeDuration-equal(A, B) xs:boolean
A eq B Gregorian Gregorian op:gYear-equal(A, B) etc. xs:boolean
A eq B xs:hexBinary xs:hexBinary op:hex-binary-equal(A, B) xs:boolean
A eq B xs:base64Binary xs:base64Binary op:base64-binary-equal(A, B) xs:boolean
A eq B xs:anyURI xs:anyURI op:anyURI-equal(A, B) xs:boolean
A eq B xs:QName xs:QName op:QName-equal(A, B) xs:boolean
A eq B xs:NOTATION xs:NOTATION op:NOTATION-equal(A, B) xs:boolean
A ne B numeric numeric fn:not(op:numeric-equal(A, B)) xs:boolean
A ne B xs:boolean xs:boolean fn:not(op:boolean-equal(A, B)) xs:boolean
A ne B xs:string xs:string fn:not(op:numeric-equal(fn:compare(A, B), 1)) xs:boolean
A ne B xs:date xs:date fn:not(op:date-equal(A, B)) xs:boolean
A ne B xs:time xs:time fn:not(op:time-equal(A, B)) xs:boolean
A ne B xs:dateTime xs:dateTime fn:not(op:datetime-equal(A, B)) xs:boolean
A ne B xdt:yearMonthDuration xdt:yearMonthDuration fn:not(op:yearMonthDuration-equal(A, B)) xs:boolean
A ne B xdt:dayTimeDuration xdt:dayTimeDuration fn:not(op:dayTimeDuration-equal(A, B) xs:boolean
A ne B Gregorian Gregorian fn:not(op:gYear-equal(A, B)) etc. xs:boolean
A ne B xs:hexBinary xs:hexBinary fn:not(op:hex-binary-equal(A, B)) xs:boolean
A ne B xs:base64Binary xs:base64Binary fn:not(op:base64-binary-equal(A, B)) xs:boolean
A ne B xs:anyURI xs:anyURI fn:not(op:anyURI-equal(A, B)) xs:boolean
A ne B xs:QName xs:QName fn:not(op:QName-equal(A, B)) xs:boolean
A ne B xs:NOTATION xs:NOTATION xs:not(op:NOTATION-equal(A, B)) xs:boolean
A gt B numeric numeric op:numeric-greater-than(A, B) xs:boolean
A gt B xs:boolean xs:boolean op:boolean-greater-than(A, B) xs:boolean
A gt B xs:string xs:string op:numeric-greater-than(fn:compare(A, B), 0) xs:boolean
A gt B xs:date xs:date op:date-greater-than(A, B) xs:boolean
A gt B xs:time xs:time op:time-greater-than(A, B) xs:boolean
A gt B xs:dateTime xs:dateTime op:datetime-greater-than(A, B) xs:boolean
A gt B xdt:yearMonthDuration xdt:yearMonthDuration op:yearMonthDuration-greater-than(A, B) xs:boolean
A gt B xdt:dayTimeDuration xdt:dayTimeDuration op:dayTimeDuration-greater-than(A, B) xs:boolean
A lt B numeric numeric op:numeric-less-than(A, B) xs:boolean
A lt B xs:boolean xs:boolean op:boolean-less-than(A, B) xs:boolean
A lt B xs:string xs:string op:numeric-less-than(fn:compare(A, B), 0) xs:boolean
A lt B xs:date xs:date op:date-less-than(A, B) xs:boolean
A lt B xs:time xs:time op:time-less-than(A, B) xs:boolean
A lt B xs:dateTime xs:dateTime op:datetime-less-than(A, B) xs:boolean
A lt B xdt:yearMonthDuration xdt:yearMonthDuration op:yearMonthDuration-less-than(A, B) xs:boolean
A lt B xdt:dayTimeDuration xdt:dayTimeDuration op:dayTimeDuration-less-than(A, B) xs:boolean
A ge B numeric numeric fn:not(op:numeric-less-than(A, B)) xs:boolean
A ge B xs:string xs:string op:numeric-greater-than(fn:compare(A, B), -1) xs:boolean
A ge B xs:date xs:date fn:not(op:date-less-than(A, B)) xs:boolean
A ge B xs:time xs:time fn:not(op:time-less-than(A, B)) xs:boolean
A ge B xs:dateTime xs:dateTime fn:not(op:datetime-less-than(A, B)) xs:boolean
A ge B xdt:yearMonthDuration xdt:yearMonthDuration fn:not(op:yearMonthDuration-less-than(A, B)) xs:boolean
A ge B xdt:dayTimeDuration xdt:dayTimeDuration fn:not(op:dayTimeDuration-less-than(A, B)) xs:boolean
A le B numeric numeric fn:not(op:numeric-greater-than(A, B)) xs:boolean
A le B xs:string xs:string op:numeric-less-than(fn:compare(A, B), 1) xs:boolean
A le B xs:date xs:date fn:not(op:date-greater-than(A, B)) xs:boolean
A le B xs:time xs:time fn:not(op:time-greater-than(A, B)) xs:boolean
A le B xs:dateTime xs:dateTime fn:not(op:datetime-greater-than(A, B)) xs:boolean
A le B xdt:yearMonthDuration xdt:yearMonthDuration fn:not(op:yearMonthDuration-greater-than(A, B)) xs:boolean
A le B xdt:dayTimeDuration xdt:dayTimeDuration fn:not(op:dayTimeDuration-greater-than(A, B)) xs:boolean
A is B node node op:node-equal(A, B) xs:boolean
A isnot B node node fn:not(op:node-equal(A, B)) xs:boolean
A << B node node op:node-before(A, B) xs:boolean
A >> B node node op:node-after(A, B) xs:boolean
A union B node* node* op:union(A, B) node*
A | B node* node* op:union(A, B) node*
A intersect B node* node* op:intersect(A, B) node*
A except B node* node* op:except(A, B) node*
A to B xs:integer xs:integer op:to(A, B) xs:integer+
A , B item* item* op:concatenate(A, B) item*
Unary Operators
Operator Operand type Function Result type
+ A numeric op:numeric-unary-plus(A) numeric
- A numeric op:numeric-unary-minus(A) numeric

C References

C.1 Normative References

XQuery 1.0 and XPath 2.0 Functions and Operators
World Wide Web Consortium. XQuery 1.0 and XPath 2.0 Functions and Operators W3C Working Draft, 15 November 2002. See http://www.w3.org/TR/xpath-functions/
XQuery 1.0 Formal Semantics
World Wide Web Consortium. XQuery 1.0 Formal Semantics. W3C Working Draft, 2 May 2003. See http://www.w3.org/TR/xquery-semantics/.
XML Schema
World Wide Web Consortium. XML Schema, Parts 0, 1, and 2. W3C Recommendation, 2 May 2001. See http://www.w3.org/TR/2001/REC-xmlschema-0-20010502/, http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/, and http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/.
XQuery 1.0 and XPath 2.0 Data Model
World Wide Web Consortium. XQuery 1.0 and XPath 2.0 Data Model. W3C Working Draft, 2 May 2003. See http://www.w3.org/TR/xpath-datamodel/.
XSLT 2.0 and XQuery 1.0 Serialization
World Wide Web Consortium. XSLT 2.0 and XQuery 1.0 Serialization. W3C Working Draft, 2 May 2003. See http://www.w3.org/TR/xslt-xquery-serialization/.
XML
World Wide Web Consortium. Extensible Markup Language (XML) 1.0. W3C Recommendation. See http://www.w3.org/TR/2000/REC-xml-20001006
XML Names
World Wide Web Consortium. Namespaces in XML. W3C Recommendation. See http://www.w3.org/TR/REC-xml-names/
ISO/IEC 10646
ISO (International Organization for Standardization). ISO/IEC 10646-1993 (E). Information technology -- Universal Multiple-Octet Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane. [Geneva]: International Organization for Standardization, 1993 (plus amendments AM 1 through AM 7).
ISO/IEC 10646-2000
ISO (International Organization for Standardization). ISO/IEC 10646-1:2000. Information technology -- Universal Multiple-Octet Coded Character Set (UCS) -- Part 1: Architecture and Basic Multilingual Plane. [Geneva]: International Organization for Standardization, 2000.
Unicode
The Unicode Consortium. The Unicode Standard, Version 2.0. Reading, Mass.: Addison-Wesley Developers Press, 1996.
Unicode3
The Unicode Consortium. The Unicode Standard, Version 3.0. Reading, Mass.: Addison-Wesley Developers Press, 2000. ISBN 0-201-61633-5.

C.2 Non-normative References

XML Query 1.0 Requirements
World Wide Web Consortium. XML Query 1.0 Requirements. W3C Working Draft, 15 Feb 2001. See http://www.w3.org/TR/xmlquery-req.
XQueryX 1.0
World Wide Web Consortium. XQueryX, Version 1.0. W3C Working Draft, 7 June 2001. See http://www.w3.org/TR/xqueryx
Editorial note  
As of the date of this publication, XQueryX has not incorporated recent language changes; it will be made consistent with this document in its next edition.
XPath 2.0
World Wide Web Consortium. XML Path Language (XPath) Version 2.0. W3C Working Draft, 2 May 2003. See http://www.w3.org/TR/xpath20/
XSLT 2.0
World Wide Web Consortium. XSL Transformations (XSLT) 2.0. W3C Working Draft. See http://www.w3.org/TR/xslt20/
XML Query Use Cases
World Wide Web Consortium. XML Query Use Cases. W3C Working Draft, 2 May 2003. See http://www.w3.org/TR/xquery-usecases/.
ISO 8601
International Organization for Standardization (ISO). Representations of Dates and Times, 2000-08-03. Available from http://www.iso.ch/

C.3 Background References

XQL
J. Robie, J. Lapp, D. Schach. XML Query Language (XQL). See http://www.w3.org/TandS/QL/QL98/pp/xql.html.
XML-QL
Alin Deutsch, Mary Fernandez, Daniela Florescu, Alon Levy, and Dan Suciu. A Query Language for XML. See http://www.research.att.com/~mff/files/final.html
SQL
International Organization for Standardization (ISO). Information Technology-Database Language SQL. Standard No. ISO/IEC 9075:1999. (Available from American National Standards Institute, New York, NY 10036, (212) 642-4900.)
ODMG
Rick Cattell et al. The Object Database Standard: ODMG-93, Release 1.2. Morgan Kaufmann Publishers, San Francisco, 1996.
Lorel
Serge Abiteboul, Dallan Quass, Jason McHugh, Jennifer Widom, and Janet L. Wiener. The Lorel Query Language for Semistructured Data. International Journal on Digital Libraries, 1(1):68-88, April 1997. See "http://www-db.stanford.edu/~widom/pubs.html
YATL
S. Cluet, S. Jacqmin, and J. Simeon. The New YATL: Design and Specifications. Technical Report, INRIA, 1999.
Quilt
Don Chamberlin, Jonathan Robie, and Daniela Florescu. Quilt: an XML Query Language for Heterogeneous Data Sources. In Lecture Notes in Computer Science, Springer-Verlag, Dec. 2000. Also available at http://www.almaden.ibm.com/cs/people/chamberlin/quilt_lncs.pdf. See also http://www.almaden.ibm.com/cs/people/chamberlin/quilt.html.
XPath 1.0
World Wide Web Consortium. XML Path Language (XPath) Version 1.0. W3C Recommendation, Nov. 16, 1999. See http://www.w3.org/TR/xpath.html

C.4 Informative Material

RFC2396
T. Berners-Lee, R. Fielding, and L. Masinter. Uniform Resource Identifiers (URI): Generic Syntax. IETF RFC 2396. See http://www.ietf.org/rfc/rfc2396.txt.
Character Model
World Wide Web Consortium. Character Model for the World Wide Web. W3C Working Draft. See http://www.w3.org/TR/charmod/
XML Infoset
World Wide Web Consortium. XML Information Set. W3C Recommendation 24 October 2001. See http://www.w3.org/TR/xml-infoset/
XPointer
World Wide Web Consortium. XML Pointer Language (XPointer). W3C Last Call Working Draft 8 January 2001. See http://www.w3.org/TR/WD-xptr
XSLT 1.0
World Wide Web Consortium. XSL Transformations (XSLT) 1.0. W3C Recommendation. See http://www.w3.org/TR/xslt

D Glossary

Editorial note  
To be done.

E Example Applications (Non-Normative)

This section contains examples of several important classes of queries that can be expressed using XQuery. The applications described here include joins across multiple data sources, grouping and aggregation, queries based on sequential relationships, and recursive transformations.

E.1 Joins

Joins, which combine data from multiple sources into a single result, are a very important type of query. In this section we will illustrate how several types of joins can be expressed in XQuery. We will base our examples on the following three documents:

  1. A document named parts.xml that contains many part elements; each part element in turn contains partno and description subelements.

  2. A document named suppliers.xml that contains many supplier elements; each supplier element in turn contains suppno and suppname subelements.

  3. A document named catalog.xml that contains information about the relationships between suppliers and parts. The catalog document contains many item elements, each of which in turn contains partno, suppno, and price subelements.

A conventional ("inner") join returns information from two or more related sources, as illustrated by the following example, which combines information from three documents. The example generates a "descriptive catalog" derived from the catalog document, but containing part descriptions instead of part numbers and supplier names instead of supplier numbers. The new catalog is ordered alphabetically by part description and secondarily by supplier name.

<descriptive-catalog>
   { 
     for $i in doc("catalog.xml")//item,
         $p in doc("parts.xml")//part[partno = $i/partno],
         $s in doc("suppliers.xml")//supplier[suppno = $i/suppno]
     order by $p/description, $s/suppname
     return
        <item>
           {
           $p/description,
           $s/suppname,
           $i/price
           }
        </item>
   }
</descriptive-catalog>

The previous query returns information only about parts that have suppliers and suppliers that have parts. An outer join is a join that preserves information from one or more of the participating sources, including elements that have no matching element in the other source. For example, a left outer join between suppliers and parts might return information about suppliers that have no matching parts.

The following query demonstrates a left outer join. It returns names of all the suppliers in alphabetic order, including those that supply no parts. In the result, each supplier element contains the descriptions of all the parts it supplies, in alphabetic order.

for $s in doc("suppliers.xml")//supplier
order by $s/suppname
return
   <supplier>
      { 
        $s/suppname,
        for $i in doc("catalog.xml")//item
                 [suppno = $s/suppno],
            $p in doc("parts.xml")//part
                 [partno = $i/pno]
        order by $p/description
        return $p/description 
      }
   </supplier>

The previous query preserves information about suppliers that supply no parts. Another type of join, called a full outer join, might be used to preserve information about both suppliers that supply no parts and parts that have no supplier. The result of a full outer join can be structured in any of several ways. The following query generates a list of supplier elements, each containing nested part elements for the parts that it supplies (if any), followed by a list of part elements for the parts that have no supplier. This might be thought of as a "supplier-centered" full outer join. Other forms of outer join queries are also possible.

<master-list>
 {
    for $s in doc("suppliers.xml")//supplier
    order by $s/suppname
    return
        <supplier>
           { 
             $s/suppname,
             for $i in doc("catalog.xml")//item
                     [suppno = $s/suppno],
                 $p in doc("parts.xml")//part
                     [partno = $i/partno]
             order by $p/description
             return
                <part>
                   {
                     $p/description,
                     $i/price
                   }
                </part> 
           }
        </supplier> 
    ,
    (: parts that have no supplier :)
    <orphan-parts>
       { for $p in doc("parts.xml")//part
         where empty(doc("catalog.xml")//item
               [partno = $p/partno] )
         order by $p/description
         return $p/description 
       }
    </orphan-parts>
 }
</master-list>

The previous query uses an element constructor to enclose its output inside a master-list element. The concatenation operator (",") is used to combine the two main parts of the query. The result is an ordered sequence of supplier elements followed by an orphan-parts element that contains descriptions of all the parts that have no supplier.

E.2 Grouping

Many queries involve forming data into groups and applying some aggregation function such as count or avg to each group. The following example shows how such a query might be expressed in XQuery, using the catalog document defined in the previous section.

This query finds the part number and average price for parts that have at least 3 suppliers.

for $pn in distinct-values(doc("catalog.xml")//partno)
let $i := doc("catalog.xml")//item[partno = $pn]
where count($i) >= 3
order by $pn
return 
   <well-supplied-item>
      <partno> {$p} </partno>
      <avgprice> {avg($i/price)} </avgprice>
   </well-supplied-item>

The distinct-values function in this query eliminates duplicate part numbers from the set of all part numbers in the catalog document. The result of distinct-values is a sequence in which order is not significant.

Note that $pn, bound by a for clause, represents an individual part number, whereas $i, bound by a let clause, represents a set of items which serves as argument to the aggregate functions count($i) and avg($i/price). The query uses an element constructor to enclose each part number and average price in a containing element called well-supplied-item.

The method illustrated above generalizes easily to grouping by more than one data value. For example, consider a census document containing a sequence of person elements, each with subelements named state, job, and income. A census analyst might need to prepare a report listing the average income for each combination of state and job. This report might be produced using the following query:

for $s in distinct-values(doc("census.xml")//state),
    $j in distinct-values(doc("census.xml")//job)
let $p := doc("census.xml")//person[state = $s and job = $j]
order by $s, $j
return 
   if (exists($p)) then
      <group>
         <state> {$s} </state>
         <job> {$j} </job>
         <avgincome> {avg($p/income)} </avgincome>
      </group>
   else ()

The if-then-else expression in the above example prevents generation of groups that contain no data. For example, the census data may contain some persons who live in Nebraska, and some persons whose job is Deep Sea Fisherman, but no persons who live in Nebraska and have the job of Deep Sea Fisherman. If output groups are desired for all possible combinations of states and jobs, the if-then-else expression can be omitted from the query. In this case, the output may include "empty" groups such as the following:

<group>
   <state>Nebraska</state>
   <job>Deep Sea Fisherman</state>
   <avgincome/>
</group>

E.3 Queries on Sequence

XQuery uses the << and >> operators to compare nodes based on document order. Although these operators are quite simple, they can be used to express complex queries for XML documents in which sequence is meaningful. The first two queries in this section involve a surgical report that contains procedure, incision, instrument, action, and anesthesia elements.

The following query returns all the action elements that occur between the first and second incision elements inside the first procedure. The original document order among these nodes is preserved in the result of the query.

let $proc := input()//procedure[1]
for $i in $proc//action
where $i >> ($proc//incision)[1]
   and $i << ($proc//incision)[2]
return $i

It is worth noting here that document order is defined in such a way that a node is considered to precede its descendants in document order. In the surgical report, an action is never part of an incision, but an instrument is. Since the >> operator is based on document order, the predicate $i >> ($proc//incision)[1] is true for any instrument element that is a descendant of the first incision element in the first procedure.

For some queries, it may be helpful to define a function that can test whether a node precedes another node without being its ancestor. The following function returns true if its first operand precedes its second operand but is not an ancestor of its second operand; otherwise it returns false:

define function precedes($a as node(), $b as node()) as boolean
{
   $a << $b
     and
   empty($a//node() intersect $b)
}

Similarly, a follows function could be written:

define function follows($a as node(), $b as node()) as boolean
{
   $a >> $b
     and
   empty($b//node() intersect $a)
}

Using the precedes function, we can write a query that finds instrument elements between the first two incisions, excluding from the query result any instrument that is a descendant of the first incision:

let $proc := input()//procedure[1]
for $i in $proc//instrument
where precedes(($proc//incision)[1], $i)
   and precedes($i, ($proc//incision)[2])
return $i

The following query reports incisions for which no prior anesthesia was recorded in the surgical report. Since an anesthesia is never part of an incision, we can use << instead of the less-efficient precedes function:

for $proc in input()//procedure
where some $i in $proc//incision satisfies
         empty($proc//anesthesia[. << $i])
return $proc

In some documents, particular sequences of elements may indicate a logical hierarchy. This is most commonly true of HTML. The following query returns the introduction of an XHTML document, wrapping it in a div element. In this example, we assume that an h2 element containing the text "Introduction" marks the beginning of the introduction, and the introduction continues until the next h2 or h1 element, or the end of the document, whichever comes first.

let $intro := input()//h2[text()="Introduction"],
    $next-h := input()//(h1|h2)[. >> $intro][1]
return
   <div>
     {
       $intro,
       if (empty($next-h))
         then //node()[. >> $intro]
         else //node()[. >> $intro and . << $next-h]
     }
   </div>

Note that the above query makes explicit the hierarchy that was implicit in the original document. In this example, we assume that the h2 element containing the text "Introduction" has no subelements.

E.4 Recursive Transformations

Occasionally it is necessary to scan over a hierarchy of elements, applying some transformation at each level of the hierarchy. In XQuery this can be accomplished by defining a recursive function. In this section we will present two examples of such recursive functions.

Suppose that we need to compute a table of contents for a given document by scanning over the document, retaining only elements named section or title, and preserving the hierarchical relationships among these elements. For each section, we retain subelements named section or title; but for each title, we retain the full content of the element. This might be accomplished by the following recursive function:

define function sections-and-titles($n as node()) as node()?
   {
   if (local-name($n) = "section")
   then element
          { local-name($n) }
          { for $c in $n/* return sections-and-titles($c) }
   else if (local-name($n) = "title")
   then $n
   else ( )
   }

The "skeleton" of a given document, containing only its sections and titles, can then be obtained by invoking the sections-and-titles function on the root node of the document, as follows:

sections-and-titles(doc("cookbook.xml"))

As another example of a recursive transformation, suppose that we wish to scan over a document, transforming every attribute named color to an element named color, and every element named size to an attribute named size. This can be accomplished by the following recursive function:

define function swizzle($n as node()) as node() 
  { 
   typeswitch($n)
     case $a as attribute(@color, *)
       return element color { string($a) } 
     case $es as element(size, *) 
       return attribute size { string($es) } 
     case $e as element() 
       return element 
         { local-name($e) } 
         { for $c in $e/(* | @*) return swizzle($c) } 
     case $d as document-node() 
       return document 
         { for $c in $d/* return swizzle($c) } 
     default return $n 
  }

The transformation can be applied to a whole document by invoking the swizzle function on the root node of the document, as follows:

swizzle(doc("plans.xml"))

F XPath 2.0 and XQuery 1.0 Issues (Non-Normative)

Values for Status has the following meaning:

resolved: a decision has been finalized and the document updated to reflect the decision.

decided: recommendations and decision(s) has been made by one or more of the following: a task-force, XPath WG, or XQuery WG.

draft: a proposal has been developed for possible future inclusion in a published document.

active: issue is actively being discussed.

unassigned: discussion of issue deferred.

subsumed: issue has been subsumed by another issue.

(parameters used: kwSort: cluster, kwFull: brief, kwDate: 00000000).


Num Cl Pr Cluster Status Locus Description Responsible
293 1 decided xquery Cdata and CharRef Semantics
444 1 decided formal-semantics Support for mixed content in the type system
96 o-1 (in)equality-operators decided xpath Normalized Equality
328 1 cdata section decided xquery What does CDATA section constructor construct?
257 D 1 collections decided xpath Does collection() always return same result?
546 1 conformance-levels active xpath Are there more processing model options that could make sense as consistent features and thus as conformance levels?
286 1 constructor-expr decided xquery Element Construction vs Streaming
290 1 constructor-expr decided xquery Element Attribute Constructor Name Type
529 1 constructor-expr decided xquery Node identity in the formal semantics
329 1 constructors decided xquery Duplicate attribute constructors
258 D 2 documents decided xpath Identity of Document Nodes
554 1 editorial active xpath What is the really normative text?
553 1 errors active xpath Rules for reporting dynamic errors statically
339 2 errors decided xquery Error type for attributes constructed too late
340 1 errors decided xpath How to identify errors?
317 1 extensions decided xquery XQuery Extension Mechanisms
538 1 extensions decided xquery Can (and should) keyword extensions be allowed in XQuery by equipping them with a namespace prefix?
272 1 external-functions decided xpath External Functions
273 1 external-objects decided xpath External Objects
555 1 formal semantics active formal-semantics Formal Semantics of Module Import
556 1 formal semantics active formal-semantics Formal Semantics of Variable Definitions
557 1 formal semantics active formal-semantics Formal semantics of Validation Declaration
558 1 formal semantics active formal-semantics The content of element types should always allow PI's and comment node types
559 1 formal semantics active formal-semantics New Sequence Type needs to be fully implemented in Formal Semantics
335 1 formal-semantics decided xpath XPath/XQuery's current semantics greatly interferes with optimization
265 2 FTTF-xml:lang decided xpath-fulltext How do we determine the xml:lang for a node if it inherits xml:lang from a higher-level node?
266 2 FTTF-xml:lang decided xpath-fulltext Do we support the sublanguage portion of xml:lang?
124 o-1 functions decided xquery External Functions
157 o-1 functions decided xquery Function Libraries
327 1 functions decided xpath Evaluate unused function parameters?
223 o-1 functions external decided xquery We need a way to declare external functions
458 1 Language active formal-semantics What is in the default context?
499 1 Language active formal-semantics Casting and validation
510 1 Language active formal-semantics Is validate working on sequences?
459 1 Language decided formal-semantics Serialization
492 1 Language decided formal-semantics Derivation by extension in XQuery
493 1 Language decided formal-semantics May the content of a text node be the empty string?
295 1 lexical-representation decided xquery Lexical Representation of Atomic Values
74 o-1 module-semantics decided xquery Module syntax
75 o-1 module-semantics decided xquery Importing Modules
79 o-1 module-syntax decided xquery Encoding
537 1 modules decided xquery What happens to imported schemas that are used in function signatures?
228 o-2 namespace functions decided xpath Should we keep the default function namespace, and the xf: namespace?
319 1 namespaces active xquery Namespace definitions and in-scope namespaces
343 1 namespaces active xpath Do functions in the null namespace clash with functions in the default namespace?
247 2 namespaces decided xpath What does default namespace(s) affect?
549 1 namespaces decided xquery Computed namespace-constructor
452 1 Semantics active formal-semantics Semantics of order by
473 1 Semantics active formal-semantics When to process the query prolog
481 1 Semantics active formal-semantics Semantics of Schema Context
496 1 Semantics active formal-semantics Support for lax and strict wildcards
508 1 Semantics active formal-semantics Namespaces in element constructors
512 1 Semantics active formal-semantics Conformance Levels
437 1 Semantics decided formal-semantics Static type errors and warnings
441 1 Semantics decided formal-semantics Implementation of and conformance levels for static type checking
450 1 Semantics decided formal-semantics Semantics of data()
453 1 Semantics decided formal-semantics Semantics of element and attribute constructors
457 1 Semantics decided formal-semantics Dynamic context for current date and time
461 1 Semantics decided formal-semantics Data model syntax and literal values
478 1 Semantics decided formal-semantics Semantics of special functions
479 1 Semantics decided formal-semantics Non-determinism in the semantics
482 1 Semantics decided formal-semantics Type equivalence rules
484 1 Semantics decided formal-semantics Treatment of nillability and xsi:nil
487 1 Semantics decided formal-semantics Representation of text nodes in formal values
491 1 Semantics decided formal-semantics Validation of an empty string against a string list
503 1 Semantics decided formal-semantics Collations in the static environment
514 1 Semantics decided formal-semantics Raising errors
520 1 Semantics decided formal-semantics Coercion between untyped and atomic values
521 1 Semantics decided formal-semantics Semantics of XPath 1.0 compatibility
525 1 Semantics decided formal-semantics Static context accessible from the dynamic context
528 1 semantics decided xpath Semantics of text constructor on empty sequence
443 1 Semantics? active formal-semantics Namespace resolution
244 2 serialization decided xquery CDATA sections and serialization
155 o-1 sort decided xquery Sorting by Non-exposed Data
243 3 sort decided xpath Provide an example of sorting "disappearing"
251 2 sort decided xquery Sorting "input to loop", not the result
318 1 sort decided xquery Add 'order by' clause to FLWR?
475 1 Static typing active formal-semantics Typing for descendant
455 1 Static typing decided formal-semantics Typing for the typeswitch default clause
472 1 Static typing decided formal-semantics Static typing of union
488 1 Static typing decided formal-semantics Static typing of path expressions in the presence of derivation by extension
509 1 Static typing decided formal-semantics Static typing for validate
513 1 Static typing decided formal-semantics Imprecise static type of constructed elements
547 1 syntax active xquery Use "declare" for declarations
548 1 syntax active xpath Lexical Rules: states normative?
550 1 syntax active xquery Location of Comments
552 1 syntax active xpath Should the quotes in processing-instruction("...") be optional?
144 o-1 syntax decided xquery Escaping Quotes and Apostrophes
246 2 syntax decided xquery Nested XQuery comments allowed?
341 1 syntax decided xpath Problems with SequenceType
532 1 syntax decided xpath Alignment between path expressions and sequence types
535 1 syntax decided xpath Lexical state tables
524 1 type semantics decided xpath Plural datatypes different from Singular *?
523 1 type-semantics active xpath input(), collection(), document(); validation semantics
534 1 type-semantics active formal-semantics Semantics of function calls and notion of "expected type"
542 1 type-semantics active formal-semantics What should be the type of an attribute or element that is well-formed but not validated, or is validated in skip mode?
43 T 1 type-semantics decided xquery Defining Behavior for Well Formed, DTD, and Schema Documents
47 T 2 type-semantics decided xquery Subtype Substitutability
48 T 3 type-semantics decided algebra CASE not a subtype
279 T 1 type-semantics decided xpath Should there be a lightweight cast?
334 T 1 type-semantics decided xpath How are documents for which validation has failed processed?
531 1 type-semantics decided xquery Should discard the type of copied subelement
533 1 type-semantics decided formal-semantics Strict static typing for automatic coercion of untyped atomic to atomic values
541 1 type-semantics decided formal-semantics Should it be a static error if an expression other than () has type empty?
543 1 type-semantics decided xpath How can a path expression match elements in the substitution group of a given element?
544 1 type-semantics decided xpath How can a path expression match nodes of a given type?
56 T 3 type-syntax decided xquery Human-Readable Syntax for Types
307 T 1 types active xpath Schema Types from input documents?
526 1 types active xpath Semantics for anySimpleType and untypedAtomic
536 1 types active xpath Data model to infoset mapping and type information
539 1 types active formal-semantics Semantics of fs:cast-untypedAtomic in backward compatibility mode
540 1 types active formal-semantics How does the static semantics works in the case where the input types are unions?
545 1 types active xpath Are XS element/attribute declarations implicitly added to the schema context?
551 1 types active xpath Constructor functions for unprefixed user defined types
206 T 2 types decided xpath Typing support in XPath
224 T 2 types decided xquery Why do we want to allow optional returns and DataType?
297 T 1 types decided xpath Should XPath have "type binding" in variable?
306 T 1 types decided xpath PSVI to Data Model mapping part of normative text?
308 T 1 types decided xpath Type Soundness
310 T 1 types decided xquery Are the children of a newly constructed element typed?
316 T 1 types decided xpath Is anySimpleType = anySimpleType*?
320 T 1 types decided xquery Should different conformance levels give the same result for the same query and data?
325 T 1 types decided xpath Refering to element that is not in the in-scope schema def.
527 1 types decided formal-semantics Static typing of XPath index expressions
486 1 Typing active formal-semantics Support for PI, comment and namespace nodes
446 1 Typing decided formal-semantics Complexity of interleaving
449 1 Typing decided formal-semantics Constraint on attribute and element content models
501 1 Typing decided formal-semantics Support for XML Schema groups
516 1 Typing decided formal-semantics Typeswitch and type substitutability
519 1 Typing decided formal-semantics Type of document node
321 1 validate decided xquery Is validate strict or lax?
322 1 validate decided xquery "validate" strict/lax override?
530 1 validation decided xquery Default default validation mode
250 2 variables decided xquery Declaring Variables in Prolog
191 o-1 whitespace decided xquery Whitespace handling in element constructors
311 1 whitespace decided xquery Whitespace and Attribute Constructors
338 1 whitespace decided xquery Handling of whitespace and character references
152 o-1 xqueryx active xqueryx XML-based Syntax

43. xquery-define-schema-variants: Defining Behavior for Well Formed, DTD, and Schema Documents

Issue Class: T Locus: xquery Cluster: type-semantics Priority: 1 Status: decided
Originator: Don Chamberlin
Defining Behavior for Well Formed, DTD, and Schema Documents

Description

We should specify the behavior of XQuery for well formed XML, XML validated by a schema, and XML validated by a DTD.

Proposed Resolution

The mapping of a DTD validated or well formed document still needs to be defined in the Data Model.

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Closing of the directly related issues: [resolved issue #xquery-abstract-syntax] and [resolved issue #xpath-issue-complex-type-value] is sufficient to close this issue.

Decision by: xpath-tf on 2003-03-04 ([link to member only information] )

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

On recommendation of the Processing Model Taskforce the disposition is reaffirmed.

47. xquery-subtype-substitutability: Subtype Substitutability

Issue Class: T Locus: xquery Cluster: type-semantics Priority: 2 Status: decided
Originator: XQuery Editors
Subtype Substitutability

Description

Should XQuery 1.0 support subtype substitutability for function parameters?

If subtype substitutability is not supported in XQuery Version 1, the motivation for TYPESWITCH is weakened and the decision to support TYPESWITCH should be revisited.

Interactions and Input

[link to member only information] Michael Rys:

I think this is still an open issue given some semantic issues that we
found between named subtype substitutability and derivation by
extension. I will send mail on this issue this week,

Actual Resolution

Addressed by the "Named Typing" proposal.

Decision by: xpath-tf on 2002-05-07 ([link to member only information] )

Decision by: xquery on 2002-05-22 ([link to member only information] )

Decision by: xsl on 2002-06-27 ([link to member only information] )

Accepting text in 2002-04-30 public draft.

48. xquery-typeswitch-case-not-subtype: CASE not a subtype

Issue Class: T Locus: algebra Cluster: type-semantics Priority: 3 Status: decided
Originator: XML Query
CASE not a subtype

Description

If the types in the CASE branches are not subtypes of the TYPESWITCH, is this an error, or are these branches simply never executed? If the latter, should we require a warning?

Actual Resolution

Decision by: xquery on 2003-02-12 ([link to member only information] )

Issue 48 closed without changes to the document (no static errors will be raised, implementations can but are not required to raise warnings).

Decision by: fs-editors on 2003-02-13 ([link to member only information] )

Decision by: xquery on 2003-02-19 ([link to member only information] )

Decision by: xsl on 2003-02-27 ([link to member only information] )

Accepting proposal in #FS-Issue-0173 closes this issue in a consistent way.

56. xquery-type-syntax: Human-Readable Syntax for Types

Issue Class: T Locus: xquery Cluster: type-syntax Priority: 3 Status: decided
Originator: Algebra Editors
Human-Readable Syntax for Types

Description

The Algebra has a syntax for declaring types. Up to now, XQuery uses XML Schema for declaring types. Is this sufficient? Some important questions:

  1. Are type names sufficient, or does XQuery really need its own syntax for declaring types?
  2. Would Normalized Universal Names (derived from MSL) be sufficient for type names?
  3. How will type names be bound to definitions?

Actual Resolution

Decision by: xquery on 2003-01-15 ([link to member only information] )Joint F2F

Decided:

Are type names sufficient - YES

Would NUNS be sufficient for type name - not needed

How will type names be bound to definitions - with imported schemas and namespaces

74. xquery-module-syntax: Module syntax

Locus: xquery Cluster: module-semantics Priority: o-1 Status: decided
Originator: XQuery Editors
Module syntax

Description

The definition and syntax of a query module are still under discussion in the working group. The specifications in this section are pending approval by the working group.

Future versions of the language may support other forms of query modules, such as update statements and view definitions.

Proposed Resolution

Paulist Modules Proposal

This proposal adds modules, external variables, external functions,
and global variables to XQuery. It addresses the following open
issues:

   74 Module syntax
   75 Importing Modules
124 External Functions
157 Function Libraries
223 We need a way to declare external functions
250 Declaring Variables in Prolog

This proposal is called the Paulist Modules Proposal, because it is
based on a simplification Paul Cotton made to earlier module
proposals, which can be found here:

  Subject: Paul's Proposal (was: Unified proposal on modules, global
           and external variables, and external functions)
  From: Jonathan Robie (jonathan.robie@datadirect-technologies.com)
  Date: Thu, Dec 19 2002
  http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0391.html

Many other people have contributed to this proposal in various
iterations, including Mary Fernandez, Jerome Simeon, Don Chamberlin,
Michael Rys, Phil Wadler, and Michael Kay.


1. Modules and Module Declarations

    An XQuery module is a resource that contains a Query. A module may
    declare a target namespace using a ModuleDecl. The syntax of Query
    and ModuleDecl is as follows:

      Query ::= ModuleDecl? QueryProlog ExprSequence?
      ModuleDecl ::= "module" ModuleURI

    If a module contains a ModuleDecl, its functions may be imported by
    other modules. A module that does not have a ModuleDecl can not be
    imported. A ModuleURI may be relative - if so, it is combined with
    the Base URI to create an absolute URI.

    In a module that is imported by another module, the optional
    ExprSequence must be absent, or a static error is raised.

2. Module Imports

    A query may import modules in the QueryProlog using
    ModuleImports. The syntax of QueryProlog and ModuleImport is as
    follows:

      QueryProlog ::=  (NamespaceDecl
                       | DefaultNamespaceDecl
                       | SchemaImport
                       | ModuleImport
                       | VarDn)*
                       FunctionDn*

      ModuleImport ::= "import" "module" ModuleURI ("at" ImplURI)?

    Functions and global variables defined in a module may be used in
    any module that imports the defining module. Importing a module
    does not provide access to the imported schemas or namespaces of
    that module. Importing a module does not provide access to the
    functions imported by that module.

    An implementation may locate a module in any convenient manner,
    provided the ModuleURI of the module it locates matches the
    ModuleURI of the ModuleImport. The optional ImplURI specifies the
    resource containing the implemenation of the module. It is treated
    like a schema location hint in XML Schema - an implementation may
    ignore it completely.

    Two modules may import each other. For instance, if module A
    imports module B, then module B may import module A.

3. Variable declarations and definitions

    A variable may be declared or defined using a VarDn in the
    QueryProlog. The syntax of VarDn is as follows:

      VarDn ::=  "define" "global"? "external"? "variable" "$" VarName
                    ("as" SequenceType)? (":=" Expr)?

    A variable may have no forward references to functions or
    variables. Functions and variables imported into a module are
    considered prior to a global variable if they are imported before
    the global variable is defined. A variable may not be used before
    it is defined.

    If the "global" keyword is present, then the variable will be
    imported whenever the module that contains it is imported.

    If the "external" keyword is present, the variable is [external];
    if it is absent, the variable is [internal].

    An [external] variable definition must include only the variable's
    name and optional sequence type, or a static error is raised.
    During dynamic evaluation, an [external] variable must be bound to
    a value in the dynamic context, or an error is raised.

    An [internal] variable definition must include the variable's name,
    optional sequence type, and a required expression, or a static
    error is raised.

    It is a type error, if the value of a variable does not match the
    declared sequence type of the variable.


4. External functions

    An external function definition allows XQuery to call functions
    written in other languages. The syntax of a FunctionDefn is as
    follows:

     FunctionDefn ::= <"define" "function"> "external"? <QName "(">
     ParamList? (")" | (<")" "as"> SequenceType)) EnclosedExpr

    If the "external" keyword is present, the function is [external];
    if it is absent, the function is [internal].

    If a function is [internal], its implementation is given as an
    XQuery expression in the module's implementation. If a function is
    [external], its implementation is given by the query environment.
    XQuery does not specify how external functions are implemented or
    accessed, how actual arguments are passed to external functions, or
    how return values are passed to the query environment - all that is
    implementation defined.

Questions in proposal that need resolution:

In today's telcon, we identified three central questions that need to
be resolved for the modules proposal. Once we resolve these questions,
it will be easy to rewrite the Paulist module accordingly.

Question 1: What is the relationship between the ModuleURI and the
namespace of the functions it contains?

Possible answers:

1.A. There is no relationship. A module is identified by a URI, and
may contain functions in any namespace.

1.B. The module URI is the namespace of functions and global variables
defined in that module. It serves as a default namespace for both
functions and global variables, but the prolog can change these
defaults.

1.C. The module URI is the namespace of functions and global variables
exported by the module. A module may contain functions and global
variables defined in other namespaces or in no namespace, but they are
not exported when the module is imported into another module.


2. Should there an optional LocationURI?

2.A. A module has an optional LocationURI, which provides the location
of a resource. This allows the name of a resource to be decoupled from
its location, while allowing relative or absolute locations to be
specified explicitly.

2.B. A module is identified only by the ModuleURI, which may be
relative or absolute. Catalogs or other similar devices are used to
map the ModuleURI onto a location.

There are two variations on 2.B:

2.B.i: The ModuleURI may be relative.
2.B.ii: The ModuleURI must be absolute.

Relative ModuleURIs are not useful if we choose 2.A.

Jonathan

Note: Michael Kay suggested Option A and Option B. They are defined as:

Option A: (C3, L1)
Option B: (C1, L2)

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Decided to adopt 1B and 2A.

75. xquery-import: Importing Modules

Locus: xquery Cluster: module-semantics Priority: o-1 Status: decided
Originator: XQuery Editors
Importing Modules

Description

The means by which a query module gains access to the functions defined an an external function library remains to be defined.

Should xmlns only be respected for construction, Xquery expressions but not functions, or also functions?

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Decided to adopt 1B and 2A in proposal for issue #xquery-module-syntax.

79. xquery-encoding: Encoding

Locus: xquery Cluster: module-syntax Priority: o-1 Status: decided
Originator: Jonathan Robie
Encoding

Description

Does XQuery need a way to specify the encoding of a query? For instance, should the prolog allow statements like the following?

ENCODING utf-16

Actual Resolution

Decision by: xquery on 2003-01-29 ([link to member only information] )

The text of a query is in Unicode. Serialization is done in Unicode, but APIs can set other encodings for serialization.

96. xquery-normalized-equality: Normalized Equality

Locus: xpath Cluster: (in)equality-operators Priority: o-1 Status: decided
Originator: Mary Fernandez
Normalized Equality

Description

When elements are compared, are comments and PIs considered in the comparison? How is whitespace handled? Do we need to allow more than one way to handle these in comparisons?

Actual Resolution

Decision by: xquery on 2002-09-04 ([link to member only information] )

Decision by: xsl on 2002-10-03 ([link to member only information] )The XSL WG is not agreeable to blessing this.

"When elements are compared, are comments and PIs considered in the comparison?": NO

"How is whitespace handled?": This depends on the whitespace in the instance as per the data model.

"Do we need to allow more than one way to handle these in comparisons?": NO, not in XPath 2.0/XQuery 1.0.

124. xquery-external-functions: External Functions

Locus: xquery Cluster: functions Priority: o-1 Status: decided
Originator: XQuery Editors
External Functions

Description

An extensibility mechanism needs to be defined that permits XQuery to access a library of functions written in some other programming language such as Java.

Some sources of information: the definition of external functions in SQL, the implementation of external functions in Kweelt.

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Decided to adopt 1B and 2A in proposal for issue #xquery-module-syntax.

144. xquery-escaping-quotes-and-apostrophes: Escaping Quotes and Apostrophes

Locus: xquery Cluster: syntax Priority: o-1 Status: decided
Originator: XML Query
Escaping Quotes and Apostrophes

Description

In attribute constructors and string constructors, XQuery uses quotes or apostrophes as delimiters. How are these characters escaped when they occur within strings that are created by one of these constructors?

Interactions and Input

[link to member only information] Michael Rys:

I asked a member of my team to check for a resolution that he can live
with. He said he has not found it and currently works on constructing
examples that shows the open issue.

Proposed Resolution

I propose that we use double-delimiters within a string literal, e.g. 'I don''t', and unlike most of my syntactic ideas, this proposal seemed to recieve general support.

Actual Resolution

Decision by: xpath-tf on 2002-04-30 ([link to member only information] )

Decision by: xquery on 2002-05-22 ([link to member only information] )

Decision by: xsl on 2002-06-27 ([link to member only information] )

Syntax in current draft has this, but explanatory text need to be added.

152. xquery-abql: XML-based Syntax

Locus: xqueryx Cluster: xqueryx Priority: o-1 Status: active
Originator: XML Query WG
XML-based Syntax

Description

XQuery needs an XML representation that reflects the structure of an XQuery query. Drafts of such a representation have been prepared, but it is not yet ready for publication.

155. xquery-phantom-sortby: Sorting by Non-exposed Data

Locus: xquery Cluster: sort Priority: o-1 Status: decided
Originator: Michael Rys
Sorting by Non-exposed Data

Description

Should we make it easier to sort by data that is not exposed in the result? Although the current language allows this, it is difficult to define complex sort orders in which some items are not exposed in the result and others are computed in the expression that is sorted. Is there a more convenient syntax for this that would be useful in XQuery?

Interactions and Input

Proposed Resolution

Here is an example:

FOR $e IN //employee
WHERE ...
RETURN
  <newe>$e/name</newe>
SORTBY
  -- Now I would like to sort by salary but cannot.

Instead, the query would have to be written as

FOR $e IN (FOR $x IN //employee RETURN $x SORTBY employee/salary/data())
WHERE ...
RETURN
  <newe>$e/name</newe>

Which seems awkward.

The question is of course how we can integrate the SORTBY in an other
way.

For example, could we say

FOR $e IN //employee
WHERE ...
SORTBY $e/salary/data()
RETURN
   <newe>$e/name</newe>

?

Best regards
Michael

Actual Resolution

Decision by: xquery on 2002-09-18 ([link to member only information] )

Decision by: xsl on 2002-10-10 ([link to member only information] )Confirming that there are no concerns for the resolution of this XQuery only issue.

Resolved by the adoption of the proposal to add "orderby" to the FLWR expression and to drop the previous "sortby" syntax/

157. xquery-function-library: Function Libraries

Locus: xquery Cluster: functions Priority: o-1 Status: decided
Originator: XQuery Editors
Function Libraries

Description

XQuery needs a mechanism to allow function definitions to be shared by multiple queries. The XQuery grammar allows function definitions to occur without a query expression.

We must provide a way for queries to access functions in libraries. For instance, we might add an IMPORT statement to XQuery, with the URI of the functions to be imported. It must be possible to specify either that (1) local definitions replace the imported definitions, or (2) imported definitions replace the local ones.

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Decided to adopt 1B and 2A in proposal for issue #xquery-module-syntax.

191. whitespace-in-element-constructors: Whitespace handling in element constructors

Locus: xquery Cluster: whitespace Priority: o-1 Status: decided
Originator: XPath Editors
Whitespace handling in element constructors

Description

How is whitespace handled in element constructors?

Issue is for material in sec 2.8. in Working Draft 2001-11-28.

Interactions and Input

[link to member only information] Michael Kay:

The XQuery WG requested information from XSL WG
as to how we currently deal with whitespace, in the hope that we can provide
an off-the-shelf solution to the problem.

In response to the action, here's a description of what XSLT does.

The stylesheet is an XML document. In constructing its infoset, all
processing instructions, comments, and whitespace-only text nodes are
discarded. (To be absolutely precise, PIs and comments are discarded; then
adjacent text nodes are merged; then whitespace-only text nodes are removed
from the tree). Whitespace text nodes are retained however, in two
circumstances: (a) if the whitespace text node is a child of an <xsl:text>
element, and (b) if an ancestor element specifies xml:space="preserve".

Certain elements in the stylesheet (for example, xsl:element) contain a
"content constructor". A content constructor is a sequence of XSLT
instructions, literal result elements, and literal text nodes. In evaluating
a content constructor, XSLT instructions do whatever the semantics of the
particular instruction say, while literal result elements and literal text
nodes are copied to the result tree.

The effect of this is that a whitespace-only text node in the stylesheet is
copied to the result tree only if either (a) it appears immediately inside
<xsl:text>, or (b) it is within the scope of an xml:space="preserve"
attribute.

Whitespace that is adjacent to non-white text in a literal text node is
copied to the result tree.

The effect of these rules is as follows:

=======================================
<a>  </a>
generates an empty element:
<a/>
=======================================
<a xml-space="preserve">  </a>
generates:
<a xml-space="preserve">  </a>
=======================================
<a><xsl:text>  </xsl:text></a>
generates:
<a>  </a>
=======================================
<a>
  <b/>
<a>
generates:
<a><b/></a>
=======================================
<a>Some text
  <b/>
</a>
generates:
<a>Some text
  <b/></a>
=======================================

There are other complications with whitespace. Whitespace in the result tree
can come from the source document as well as from the stylesheet; XSLT
provides control over whether whitespace-only text nodes in the source
document are significant or not. Whitespace can also be generated in the
output during serialization, if the xsl:output option indent="yes" is
specified.

Also of course the XSLT rules apply in addition to the XML rules. XML for
example normalizes line endings and normalizes whitespace (but not 

character references) in attribute values. This happens outside XSLT's
control. Whitespace character references such as   are treated
differently from literal whitespace by the XML processor, but are treated
identically to literal whitespace by the XSLT processor.

It's fair to say that these rules create a fair bit of confusion. It usually
doesn't matter for generating HTML, because whitespace in HTML is rarely
significant. For generating text files, it can be quite tricky. However, the
rules are well-defined and a user who understands the rules can always get
the required output.

What should XQuery do? I'd suggest mimicking these rules as closely as
possible, if only because users then only have to learn one set of confusing
rules rather than two. I can't think of any obvious improvements that would
make the system less confusing. Where the user wants to explicitly output
whitespace, of course, <a>{'  '}</a> provides a suitable alternative to
XSLT's <xsl:text> instruction.

This analogy would suggest that <a>  {'x'}  </a> should output <a>x</a>,
while <a>z {'x'} y</a> should output <a>z x y</a>: that is, the characters
between <a> and "{" are ignored if they consist entirely of whitespace, but
are all significant if any of them is non-whitespace. <a> </a> should output
<a/>, as should <a> </a>. This is only a suggestion, of course, the
decision is entirely for XQuery to make.

Mike Kay

Actual Resolution

Decision by: xquery on 2002-09-11 ([link to member only information] )

Decided: Resolve this by adopting the whitespace proposal.

206. xpath-datatype-support: Typing support in XPath

Issue Class: T Locus: xpath Cluster: types Priority: 2 Status: decided
Originator: Mike Kay
Typing support in XPath

Description

Which of these type productions (CAST, TREAT, ASSERT, TYPESWITCH...) belong in XPath? (ie common to XQuery and XPath)

The list is now (2002-10): CAST, TREAT, VALIDATE, INSTANCE OF, types on variable bindings, TYPESWITCH.

Actual Resolution

Decision by: xsl on 2003-04-07 ([link to member only information] )

Decision by: xquery on 2003-04-09 ([link to member only information] )

Decided to remove "validate" from XPath. ("typeswitch" was removed already)

223. external-function-definition: We need a way to declare external functions

Locus: xquery Cluster: functions external Priority: o-1 Status: decided
Originator: Michael Rys
We need a way to declare external functions

Description

Should we allow external functions to be defined using a syntax like this?

       [71a] ExternalFnDef ::= {"define" S "external" S "function"}
            QName "(" ParamList? ")" ("returns" Datatype)?
 

Interactions and Input

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Decided to adopt 1B and 2A in proposal for issue #xquery-module-syntax.

224. function-return-datatype: Why do we want to allow optional returns and DataType?

Issue Class: T Locus: xquery Cluster: types Priority: 2 Status: decided
Originator: Michael Rys
Why do we want to allow optional returns and DataType?

Description

Would we prefer a syntax that requires explicit declaration of a general type when a function is to be loosely typed, rather than use the current syntax in which the type is omitted when the function is untyped.

Actual Resolution

Decision by: xquery on 2003-02-12 ([link to member only information] )

Decided that the default is item*.

228. default-namespace-functions: Should we keep the default function namespace, and the xf: namespace?

Locus: xpath Cluster: namespace functions Priority: o-2 Status: decided
Originator: Scott Boag
Should we keep the default function namespace, and the xf: namespace?

Description

The question was raised of whether the Query WG and F&O TF have 1) a good rationale for putting built-in functions in a namespace, and 2) a consistent story about how this will relate to default namespace declarations and user-defined functions.

It would seem odd to have to have all user defined functions put in the FandO namespace if a namespace is not declared for it. If you do not do that, then user defined functions that don't require a prefix will not match the QName.

And, if there is not a good rational that provides user benifits, then it seems like we are going through a lot of additional complexity for little or no benefit.

Interactions and Input

[link to member only information] Kristoffer Rose:

Actual Resolution

Decision by: xquery on 2003-01-22 ([link to member only information] )Unqualified, user-defined functions are placed in the default namespace for the scope of the query *only*.

Decision by: xsl on 2003-01-16 ([link to member only information] )

This issue is identical to XSLT issue 155. Decision:

- no controls on default function namespace

- XSLT functions are in F&O namespace

- User defined function must be in a namespace

243. sort-disappearing: Provide an example of sorting "disappearing"

Locus: xpath Cluster: sort Priority: 3 Status: decided
Originator: Michael Rys
Provide an example of sorting "disappearing"

Description

Provide an example of

   (employee sortby data(salary))/name
 

Actual Resolution

Decision by: xquery on 2002-09-11 ([link to member only information] )

Decision by: xsl on 2002-10-10 ([link to member only information] )

Decided to leave this to editorial discretion.

244. cdata-serialization: CDATA sections and serialization

Locus: xquery Cluster: serialization Priority: 2 Status: decided
Originator: Michael Rys
CDATA sections and serialization

Description

What are the semantics of CDATA sections in XQuery? Are they preserved in the data model for serialization?

Actual Resolution

Decision by: xquery on 2002-12-11 ([link to member only information] )

Decided to close, with document changes as described by Mike Kay in http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0095.html, including editorial comments.

246. nested-comments: Nested XQuery comments allowed?

Locus: xquery Cluster: syntax Priority: 2 Status: decided
Originator: Michael Rys
Nested XQuery comments allowed?

Description

Nested XQuery comments allowed?

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

Permit nested comments. Use "(:" and ":)" syntax.

247. namespace-default-affecting: What does default namespace(s) affect?

Locus: xpath Cluster: namespaces Priority: 2 Status: decided
Originator: XPath TF
What does default namespace(s) affect?

Description

What is effect of default namespace declarations on unprefixed QNames that may occur in element constructors, attribute constructors, and name tests (or anywhere else).

In XPath 1.0, in-scope namespace decls effect prefixed QNames, but default namespace decl does not effect unprefixed names in a name test. In XSLT 2.0, we introduced multiple default namespace decls :one for constructed elements, one for names in xpath expressions.

Actual Resolution

Decision by: xquery on 2002-09-11 ([link to member only information] )

Decided to accept status quo:

- default element namespace defines a namespace URI that is associated with unprefixed names of elements and types.

- default function namespace defines a namespace URI that is associated with unprefixed names of functions.

250. declaring-variables-in-prolog: Declaring Variables in Prolog

Locus: xquery Cluster: variables Priority: 2 Status: decided
Originator: Jonathan Robie
Declaring Variables in Prolog

Description

Functions in a function library often need to access the same variables. For instance, a function library that manipulates a grammar may need to use the following variables in many functions:

$grammar := document("xpath-grammar.xml")/g:grammar
$target := "xquery"

One possible syntax for this is:

'define' ''variable' varname ':=' expr

The above production would occur only in the prolog.

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Decided to adopt 1B and 2A in proposal for issue #xquery-module-syntax.

251. sort-by: Sorting "input to loop", not the result

Locus: xquery Cluster: sort Priority: 2 Status: decided
Originator: Phil Wadler
Sorting "input to loop", not the result

Description

Consider this query:

   for $x in /books/book, $y in /reviews/review
   where $x/isbn = $y/isbn
   return <newbook>{ $x/title, $x/author, $y/reviewer }</newbook>
   sortby isbn

This is an error, since isbn doesn't appear in newbook. (The static type system would catch this error.) What you have to write is

   for $z in
     for $x in book, $y in review
     where $x/isbn = $y/isbn
     return <dummy>{ $x/title, $x/author, $y/reviewer, $x/isbn }</dummy>
     sortby isbn
   return <newbook>{ $z/title, $z/author, $z/reviewer }</newbook>

This is painful.

I think that XQuery should support this syntax, or something similar:

   for $x in book, $y in review
   where $x/isbn = $y/isbn
   sortby $x/isbn
   return <newbook>{ $x/title, $x/author, $y/reviewer }</newbook>

Our plate is full with more important matters just now, but I hope we could fix this before we finalize XQuery.

Actual Resolution

Decision by: xquery on 2002-09-18 ([link to member only information] )

Decision by: xsl on 2002-10-10 ([link to member only information] )Confirming that there are no concerns for the resolution of this XQuery only issue.

Resolved by the adoption of the proposal to add "orderby" to the FLWR expression and to drop the previous "sortby" syntax.

257. collection-always-return-same: Does collection() always return same result?

Issue Class: D Locus: xpath Cluster: collections Priority: 1 Status: decided
Originator: XPath TF
Does collection() always return same result?

Description

Does collection() always return same result for the same URI? The same within the scope of a query/transformation? Are the nodes in the sequence identical?

Actual Resolution

Decision by: xpath-tf on 2002-10-16 ([link to member only information] )

Decision by: xquery on 2002-10-23 ([link to member only information] )

Decision by: xsl on 2002-10-31 ([link to member only information] )

It should return the same answer every time. Applies also to input(). We should use the same language as we use for document() and for current-dateTime().

258. document-nodes-identity: Identity of Document Nodes

Issue Class: D Locus: xpath Cluster: documents Priority: 2 Status: decided
Originator: Jonathan Robie
Identity of Document Nodes

Description

Consider the following query:

        if (document("foo.com") == document("foo.com"))
                then <yep/>
                else <nope/>

I would like the following output:

        <yep/>

I think we can achieve this if we say that the URI of a resource is used as its identity. However, one resource can be identified by more than one URI. Suppose that "foo.com/here/there/hi.xml" and "file://c:/temp/limerick-tei.xml" refer to the same resource. What does the following return?

if (document("foo.com/here/there/hi.xml") ==
document("file://c:/temp/limerick-tei.xml"))
        then <yep/>
        else <nope/>

Should we simply use the URI of the parameter to establish identity and say that the two do not match? Should we make the result implementation-dependent?

Actual Resolution

Decision by: xpath-tf on 2002-10-16 ([link to member only information] )

Decision by: xquery on 2002-10-23 ([link to member only information] )

Decision by: xsl on 2002-10-31 ([link to member only information] )

This is already covered by the existing spec, but we may want to review the language as part of the actions for issue 257.

265. lang-inheritance: How do we determine the xml:lang for a node if it inherits xml:lang from a higher-level node?

Locus: xpath-fulltext Cluster: FTTF-xml:lang Priority: 2 Status: decided
Originator: FTTF
How do we determine the xml:lang for a node if it inherits xml:lang from a higher-level node?

Description

How do we determine the xml:lang for a node if it inherits xml:lang from a higher-level node?

Actual Resolution

Decision by: xquery on 2003-02-12 ([link to member only information] )

Decided to close issue with no change to documents, since user-written expressions or functions can determine the value of xml:lang that a node inherits.

266. lang-sublanguage-support: Do we support the sublanguage portion of xml:lang?

Locus: xpath-fulltext Cluster: FTTF-xml:lang Priority: 2 Status: decided
Originator: FTTF
Do we support the sublanguage portion of xml:lang?

Description

Do we support the sublanguage portion of xml:lang? If so, how?

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

A user-written expression of function has to determine the value of xml:lang and then do the appropriate analysis of the value. No change to document.

272. external-functions: External Functions

Locus: xpath Cluster: external-functions Priority: 1 Status: decided
Originator: Michael Kay
External Functions

Description

The ability to call external functions is an established feature of XSLT 1.0, and is retained in XSLT 2.0. The facility is widely used, and some significant libraries of external functions have been developed by third parties. We made an attempt to standardize language bindings for external functions in the XSLT 1.1 working draft, but this proved highly controversial and has been dropped. The facility remains, however, even though the binding mechanisms remain implementation-defined.

The XPath 2.0 specification continues to tolerate external functions, though it doesn't really acknowledge their existence properly. All we say is that the repertoire of functions that can be called is part of the context.

The issue is: should the function function-available() function be transferred from XSLT to XPath?

This function tests whether a named function is available, and returns true if it is, and false if it isn't. A typical call is:

if  (function-available('my:debug')) then my:debug('Hi!') else ()

This has two implications:

(a) a call on my:debug must not be a static error if the function is not available

(b) the names of functions (and the in-scope namespaces needed to resolve their QNames) must be available at run-time.

Logically the function-available() function has no dependencies on XSLT so it should be transferred to XPath.

Actual Resolution

Decision by: xpath-tf on 2002-12-10 ([link to member only information] )

Proposed to resolve by stating that the XPath specification to state that at the discretion of the host language, a call to a function that is not in the static context may generate a dynamic error rather than a static error.

Decision by: xquery on 2003-02-26 ([link to member only information] )

This issue is also impacted by the following decision:

Decided to adopt 1B and 2A in proposal for issue #xquery-module-syntax.

273. external-objests: External Objects

Locus: xpath Cluster: external-objects Priority: 1 Status: decided
Originator: Michael Kay
External Objects

Description

Part of the strength of external functions is that they can return objects that are outside the scope of the XPath type system. For example, a function library for performing SQL database access may have a function sql:connect() that returns an object representing a database connection. This object may be passed as an argument to calls on other functions in the SQL function library.

The way this is handled in XPath 1.0 is that the XPath specification defines four data-types, and explicitly leaves the host language free to define additional data types. We could probably live with a similar solution for XPath 2.0, but it's a fudge, and I think we ought to try and do better.

Note that the only things you can do with an external object (under the XSLT 1.0 rules) are to assign it to a variable, or pass it as the argument to another function. In practice I think implementations also allow external objects to have additional behavior, for example they might allow conversion to a string when used in a context where a string is required. I think we should leave such behavior implementation-defined rather than saying that it is always an error.

The question arises as to where external objects should fit into the type hierarchy. Should they be a top-level thing at the same level as "sequence", or should they be one level down, along with "node" and "atomic value"? I think it makes most sense to preserve the principle "everything is a sequence", which means that there are now three kinds of item: nodes, atomic values, and external objects.

Handling this rigorously sounds like quite a pervasive change to the spec, but I don't think it's as bad as it seems. I don't think we should add any language features to support external objects, with the possible exception of a keyword "external" in the type syntax so that one can test for it using "instance of". Functions and operators that work on any sequence (for example, count) should treat an external object like any other item in the sequence. Operations that expect nodes will fail if presented with an external object; operations that expect atomic values will also fail, except that implementations may define fallback conversions from external objects to atomic values.

Interactions and Input

Proposed Resolution

Technically, I believe we could close the issue with no change to the documents, on the basis that the definition for the static context (in both XPath and XQuery) states: "Additional type definitions may be added to the in-scope type definitions by the language environment." I think an implementation could take this as sufficient authority to extend the type hierarchy with additional types, including types needed to represent objects returned by extension functions (such as "an SQL database connection").

Editorially, I think it would be a good idea if we state this explicitly in a Note, as follows:

NOTE: an implementation may allow function calls in a Query/Expression to bind to functions written in languages that use a different type system (these are known as "extension functions" in XSLT, "external functions" in XQuery). In this case, the way in which the arguments and results of such functions are mapped between the two type systems is implementation-defined. An implementation may define new types anywhere within the type hierarchy of the [Data Model] that are designed to facilitate interworking with other languages, for example a type that encapsulates an object returned by an external function; or it may provide mechanisms for the user to define such types.

Actual Resolution

Decision by: xpath-tf on 2003-03-11 ([link to member only information] )

Decision by: xquery on 2003-03-19 ([link to member only information] )

Proposal accepted.

279. xpath-lightweight-cast: Should there be a lightweight cast?

Issue Class: T Locus: xpath Cluster: type-semantics Priority: 1 Status: decided
Originator: Jonathan Robie
Should there be a lightweight cast?

Description

Should there be any provision for a lightweight cast that does not observe facets? Phil Wadler has suggested that 'validate' be used whenever full schema validation is desired, and 'cast' be used as a lightweight validation, which can be used for either simple or complex types, but which does not supply defaults, enforce facets, or check integrity constraints. It may be easier to optimize through cast than through validate, but supporting both constructs may confuse users due to their similarity. He suggests the following syntax for these expressions:

('cast'|'validate') as SequenceType ()
('cast'|'validate') 'in' ContextExpr { Expr }

Actual Resolution

Decision by: xquery on 2002-09-11 ([link to member only information] )

Decision by: xsl on 2002-10-10 ([link to member only information] )

Decided to reject this proposal. Cast checks all facets.

286. element-construction-vs-streaming: Element Construction vs Streaming

Locus: xquery Cluster: constructor-expr Priority: 1 Status: decided
Originator: Michael Rys
Element Construction vs Streaming

Description

The element construction rules in 2.8 make efficient streaming of element construction difficult/impossible. For example, we execute the following expression on a stream and serialize the result in a streaming processing (such as XSLT like applications):

<foo>{"foo", "bar", if (expr) then "baz" else <baz/>}</foo>

If expr is true, then this is serialized:

<foo>foo bar baz</foo>

If expr is false, then this is serialized: <foo>foobar<baz/></foo>

The implementation must cache up the "foo" and "bar" strings, just in case a sub-element node is constructed. If not, then I must insert a space between "foo" and "bar". This seems to contradict one of our explicit use scenarios in the XML Query Requirements (section 2.5).

Interactions and Input

Actual Resolution

Decision by: xquery on 2002-09-04 ([link to member only information] )

This issue has been addressed by the recent changes to the element constructor.

290. element-attribute-constructor-name-type: Element Attribute Constructor Name Type

Locus: xquery Cluster: constructor-expr Priority: 1 Status: decided
Originator: Michael Rys
Element Attribute Constructor Name Type

Description

Does the name expression on dynamically computed names in element/attribute constructors be of type QName without implicit cast from string, QName with implicit cast from string, or string?

Proposed Resolution

If the name is constructed by an expression, the expected type is xs:QName. Xs:string is in general implicitly cast to xs:QName (and xs:anyURI).

Proposed Resolution

(1) In Section 3.7.1 ("Direct Element Constructors"), modify the paragraph below the first example as follows:

"Unqualified element names used in a direct element constructor are implicitly qualified by the default namespace for element names. In a direct element constructor, the name used in the end tag must exactly match the name used in the corresponding start tag (including its prefix or absence of a prefix)."

(2) In Section 3.7.2.1 ("Computed Element Constructors"), add a new first paragraph as follows:

"The name expression of a computed element constructor is processed as follows:

1. If the name expression returns a QName, that QName is used as the name of the constructed element. If the QName returned by the name expression is unqualified, the name of the constructed element is in default namespace for element names.

2. If the name expression returns a string, that string is implicitly cast to a QName by using the fn:QName-in-context function with its $use-default parameter set to True. The resulting QName is used as the name of the constructed element.

3. If the name expression does not return a QName or a string, a dynamic error is raised."

(3) In Section 3.7.2.2 ("Computed Attribute Constructors"), add a new first paragraph as follows:

"The name expression of a computed attribute constructor is processed as follows:

1. If the name expression returns a QName, that QName is used as the name of the constructed attribute. If the QName returned by the name expression is unqualified, the name of the constructed attribute is in no namespace.

2. If the name expression returns a string, that string is implicitly cast to a QName by using the fn:QName-in-context function with its $use-default parameter set to True. The resulting QName is used as the name of the constructed attribute.

3. If the name expression does not return a QName or a string, a dynamic error is raised."

Actual Resolution

Decision by: x-editors on 2003-02-05 ([link to member only information] )

Decision by: xquery on 2003-02-12 ([link to member only information] )

Recommend Don's proposal as the closure of this issue.

293. cdata-charref-semantics: Cdata and CharRef Semantics

Locus: xquery Cluster: Priority: 1 Status: decided
Originator: Michael Rys
Cdata and CharRef Semantics

Description

The data model cannot represent CDATA or CharRef, since the Information Set looses this information.

Proposed Resolution

The XQuery document should make it clear that:

1. CDATA sections and CharRefs inside XQueries that are not embedded inside XML (which is what the XQuery document only talks about), are syntactic helps to write queries that otherwise would need entitization (in the case if CDATA sections) or a unicode input device (CharRefs).

2. Implementations can chose to use this information as serialization hints to preserve the CDATA and entitization.

Actual Resolution

Decision by: xquery on 2002-12-11 ([link to member only information] )

Decided to close, with document changes as described by Mike Kay in http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0095.html, including editorial comments.

295. lexical-representation-of-atomic-values: Lexical Representation of Atomic Values

Locus: xquery Cluster: lexical-representation Priority: 1 Status: decided
Originator: xquery/xsl f2f
Lexical Representation of Atomic Values

Description

The wording in section 2.8.3 needs to be aligned with Data model and F&O; 'lexical representation' needs to be defined differently and be consistent in XQuery, Datamodel, F&O. It probably needs to be string value (canonical value of integer in W3C Schema has a "." so not appropriate [or we need to have our own definition of the canonical value...]).

Actual Resolution

Decision by: xsl on 2003-03-06 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-06 ([link to member only information] )Joint meeting

3.7.2.4 "text node constructors", that's the one that should be aligned to "string-value".

297. binding: Should XPath have "type binding" in variable?

Issue Class: T Locus: xpath Cluster: types Priority: 1 Status: decided
Originator: XQuery Editors
Should XPath have "type binding" in variable?

Description

The 2002-06-24 grammar introduces the "binding" production. "assert" is removed from both XQuery and XPath. "binding" currently requires reserved words. Should "binding" be in XPath?

Several reasons NOT to include it in XPath:

- grammar

- semantics don't match function call semantics

- rarely useful

- reads oddly for range variables if (some integer $x in (1,2,"fred") satisfies $x=1)

- biggest of all, users are asking us to simplify. We will get a very adverse reaction if we make "for" expressions more complicated.

But it is worrying to have such a big split between XPath and XQuery.

Actual Resolution

Decision by: xpath-tf on 2002-11-12 ([link to member only information] )

Decision by: xsl on 2002-11-14 ([link to member only information] )

Decision by: xsl on 2003-01-09 ([link to member only information] )

Closed based on the XSLT recommendation to not include type declarations in XPath.

306. PSVI-Data-Model-mapping-normative: PSVI to Data Model mapping part of normative text?

Issue Class: T Locus: xpath Cluster: types Priority: 1 Status: decided
Originator: Don Chamberlin
PSVI to Data Model mapping part of normative text?

Description

Should the mapping from PSVI to Query Data Model be part of the normative language specification? (The mapping is affected by the presence or absence of the Schema Import Feature).

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Close issue: mapping already exists and is Normative).

307. schema-types-from-input-documents: Schema Types from input documents?

Issue Class: T Locus: xpath Cluster: types Priority: 1 Status: active
Originator: Don Chamberlin
Schema Types from input documents?

Description

During the analysis phase, in-scope schema definitions are derived from schemas named in Schema Import clauses.

Should there be additional in-scope schema definitions that are part of the static context? Should there be another set of in-scope schema definitions that are part of the dynamic context? What would that do to static typing? Would this interfere with interoperability?

In particular:

1. Should an environment be allowed to statically predefine schema definitions for a query? This would allow queries on fixed collections or known message types to provide strong type information without forcing users to explicitly import the corresponding schemas.

2. How does type information found dynamically in queried documents affect the query environment?

Does data() dynamically use the type information found in the instances that are queried, even when the types have not been declared in imported schemas? Note that Basic XQuery does not work properly if this is not true, since it must be able to discover the types of elements without importing their definition.

May an instance contain types that have not been imported into the static environment? If we say it may not, then schema imports are needed to query any document that contains types that are not predefined in XQuery.

May documents that are queried have different definitions for the same names? Note that solutions that dynamically load type information from a document into the in-scope schema definitions may try to introduce all such definitions into the static environment, which should cause an error according to our current rules.

Proposed Resolution

If we want Basic XQuery to be able to query documents that have types that are not predefined, then data() must be able to use type information from instances. But if we want to be able to query validated documents that have different schemas this information must not be added to the static environment (or else we must find a way to add more than one schema definition for a given name to the static environment, or say that the static environment is dynamic, or....).

My tentative conclusions:

1. The in-scope schema definitions should be determined statically.

2. data() and many operators must be able to utilize the type information found in a document.

3. As a matter of convenience, it should be possible to import the schemas associated with a single document or with all documents in a collection. For instance, a syntax like the following may be useful:

import schema from collection
"jdbc:datadirect:sqlserver://localhost:1433;database='airports'"

or

import schema from document
"file:///C:/projects/query/requirements/xml-spec.xsd"

4. Implementations should be allowed to implicitly import schemas into the environment before executing a query, using any of the approved ways above.

Proposed Resolution

Proposal (3): Types in Queries, Types in Documents

This proposal distinguishes the relationship between types known statically in the query and types that are discovered dynamically in documents during query processing. This version of the proposal follows the results of a telcon on the subject, as recorded in:

Re: Issue 307 Telcon: Friday, 15 Nov, 12:00 EST From: Jonathan Robie (jonathan.robie@datadirect-technologies.com) Date: Fri, Nov 15 2002 http://lists.w3.org/Archives/Member/w3c-query-editors/2002Nov/0148.html

This proposal addresses the following issue:

Issue 307 schema-types-from-input-documents: Schema Types from input documents?

And here is the proposal itself:

1. Static Types in Queries

Implementations are allowed to implicitly import schemas into the environment before executing a query. The in-scope schema definitions are determined statically, containing the built-in type definitions, any schemas imported explicitly into the query, and any schemas imported implicitly from the query environment.

In a query, it is a static error to use a name in a SequenceType production if the name is not found in the in-scope schema definitions.

2. Types in Input Documents

An input document may be accessed via an input function or via an externally defined variable that is bound to the input document by the query environment. An input document may refer to type names that have not been imported into the in-scope schema definitions, but it must not contain types that have the same names as types in the static environment, but conflicting definitions. Input functions and the query environment must promote unknown type names to the nearest type name in the in-scope schema definitions that is known to be substitutable for the unknown type name. If the unknown type name is derived from a known type by extension, list, or union, then the type name is changed to xs:anySimpleType if it is a simple type, or to xs:anyType if it is a complex type. This loses type information, but ensures that all type names in input documents are also in the in-scope schema definitions.

Note: This approach guarantees that the built-in types and the static in-scope-schema definitions are the only types found in an input document. As a result, there is no need to extend the known types when a new document is read.

Note: One ramification of this approach is that types derived by extension are not substitutable for their base types unless the schemas defining these types are imported into the query. We consider this a fair tradeoff for type safety. If people want to exploit the full type hierarchy, they need to import the schema that defines it.

Note: Mapping all the types when an input function is called is obviously an inefficient implementation strategy. Many implementations will take a different approach, but this is a simple way to specify the desired behavior.

Actual Resolution

Decision by: xquery on 2002-12-04 ([link to member only information] ) Proposal (3) accepted.

Decision by: xpath-tf on 2003-03-25 ([link to member only information] ) Revoke resolution of Issue 307. Type annotations are not "dumbed down".

308. type-soundness: Type Soundness

Issue Class: T Locus: xpath Cluster: types Priority: 1 Status: decided
Originator: Don Chamberlin
Type Soundness

Description

The Static Typing Feature is claimed to have a property called "type soundness." However, Dana says she has counterexamples to the claim of type soundness as described in this section (Section 2.4.2.3). (At least sequence type matching breaks TYPE SOUNDNESS so what else breaks it?) We need to examine the claim and make sure it is stated correctly.

Actual Resolution

Decision by: xpath-tf on 2002-11-12 ([link to member only information] )

Decision by: xsl on 2002-11-14 ([link to member only information] )

Decision by: xsl on 2003-01-09 ([link to member only information] )

Closed due to the definition of type errors in language and FS books.

310. type-annotations-child-of-element: Are the children of a newly constructed element typed?

Issue Class: T Locus: xquery Cluster: types Priority: 1 Status: decided
Originator: Dana F
Are the children of a newly constructed element typed?

Description

What happens with the type annotation of the children of a newly constructed element? Type annotation kept or given xs:anyType.

Actual Resolution

Decision by: xquery on 2002-12-18 ([link to member only information] )

Decision to accept the propsal of Phil Wadler in http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0378.html.

Decision by: xquery on 2003-01-29 ([link to member only information] )

Decided to reopen the issue.

Decision by: xquery on 2003-03-06 ([link to member only information] )

Decided NOT to reopen the issue.

311. whitespace-attribute-constructors: Whitespace and Attribute Constructors

Locus: xquery Cluster: whitespace Priority: 1 Status: decided
Originator:
Whitespace and Attribute Constructors

Description

Whitespace in an XSLT attribute value template is significant insofar as it survives the XML rules for normalization of attributes. This means that CRLF combinations and tabs are normalized to x20 spaces, unless they are written as XML character references. I think it's an open question whether XQuery wants to emulate the XML attribute normalization rules.

In XSLT,

<foo bar="
   {'x'}
"/>

will produce the result <foo bar=" x "/>

while <foo bar=""/> produces an element containing an attribute whose value is a single CR character.

If XQuery wants to reproduce this behavior exactly, then it's going to have to reproduce the XML treatment of whitespace as well as the XSLT treatment.

But whether it does so or not, I think Mary is right that

<foo bar=" {'x'} "/>

should produce lt;foo bar=" x "/> and not <foo bar="x"/>. There is a difference between element and attribute constructors: attributes have quotes around them, and this sets a different expectation.

Actual Resolution

Decision by: xquery on 2002-12-04 ([link to member only information] )

Confirmed that Mary's proposal for whitespace, that was accepted 2002-11-27, closes this issue.

Decision by: xquery on 2002-12-11 ([link to member only information] )

Resolved by the recent adoption of the revised text on attribute constructors.

316. cardinality-typed-comparison: Is anySimpleType = anySimpleType*?

Issue Class: T Locus: xpath Cluster: types Priority: 1 Status: decided
Originator: Michael Rys
Is anySimpleType = anySimpleType*?

Description

Given the following function:

define function foo(xs:anySimpleType $x) returns xs:anySimpleType {$x}

and the untyped data

<a a="1"/><a a="2"/><a a="3"/>

should the following be a (static or dyamic) type error or should it work?

foo(/a/@a)

If it should work, what should the following query return?

count(data(<e>1 2</e>))
count(data(<a b="1 2"/>/@b))

Should it be 1 or 2?

Proposed Resolution

anySimpleType is the base type of all the *primitive* XML Schema datatypes.

List and union types are *generated* (my word, Schema uses the word *derived*) from primitive types and thus, not included in anySimpleType. See the extract from the XML Schema datatypes spec below.

"[Definition:] There exists a conceptual datatype, whose name is anySimpleType, that is the simple version of the ur-type definition from [XML Schema Part 1: Structures]. anySimpleType can be considered as the *base type* of all *primitive* types. The *value space* of anySimpleType can be considered to be the *union* of the *value space*s of all *primitive* datatypes."

Thus, the function call above should result in a (static or dynamic, depending on typing conformance) type error.

The count expressions would always return 1.

Actual Resolution

Decision by: xpath-tf on 2002-12-17 ([link to member only information] )

Decided that anySimpleType is a list one. This needs to be carried out clearly in the documents.

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

To solve issues 316 and 524 we need to do eliminate three constructor functions from F&O, and integrating with the changes described in the message: http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Mar/0021.html.

This was agreed.

317. extension-mechanism: XQuery Extension Mechanisms

Locus: xquery Cluster: extensions Priority: 1 Status: decided
Originator: Andrew Eisenberg
XQuery Extension Mechanisms

Description

Issue: XQuery has not determined what extension mechanisms might be supported. XQuery may support the following:

  • implementation-defined extensions to the XQuery grammar
  • an XQuery-flagger that identifies extensions to XQuery 1.0
  • implementation-defined extensions to the functions that are available to
  • an XQuery author. The author would be required to explicitly declare the
  • namespaces of any extension functions that are used

Interactions and Input

Proposed Resolution

This proposal adds the following to the XQuery language document (in
section 2.5 Errors and Conformance):


2.5.5 Extensions

Conforming XQuery implementations are permitted to make two different kinds
of extensions to the specifications: grammar extensions and semantic
extensions. There are two types of grammar extensions: pragmas and
must-understand extensions. While an XQuery implementation may support some
or all of these types of extensions, this does not negate the requirement
to support the XQuery functionality defined in this specification.


2.5.5.1 Pragmas

A pragma may be used to provide additional information to an XQuery
implementation.

[x1]  Pragma            ::=   "(::" "pragma" PragmaQName PragmaContents
"::)"

[x2]  PragmaQName       ::=   ExplicitQName

[x3]  ExplicitQName     ::=   QName

[x4]  PragmaContents    ::=   .*

An ExplicitQName requires that QName contain a Prefix. Pragmas may be used
anywhere that ignorable whitespace is allowed, and within element content.
See A.1 Lexical structure for the exact lexical states where pragmas are
recognized. A pragma is identified by its PragmaQName.

If an implementation does not support a pragma, then that pragma shall be
ignored. If an implementation does support a pragma and the implementation
determines that the PragmaContents are invalid, then a static error is
raised. Otherwise, the effect of the pragma on the result of the Query is
implementation-defined.

The following example shows how a pragma might be used:

   declare namespace exq = "http://example.org/XQueryImplementation"

   (:: pragma exq:timeout 1000 ::)

   count(input()//author)

An implementation that supports the exq:timeout pragma might raise a
dynamic  error if it is unable to count the authors within 1000 seconds. An
implementation that did not support this pragma would execute as long as
necessary to count the authors.


2.5.5.2 Must-Understand Extensions

An implementation may extend the XQuery grammar by supporting
must-understand extensions.

[y1]  MustUnderstandExtension ::=
            "(::" "extension" ExtensionQName ExtensionContents "::)"

[y2]  ExtensionQName          ::=   ExplicitQName

[y3]  ExtensionContents ::=   .*

A MustUnderstandExtension may be used anywhere that ignorable whitespace is
allowed, and within element content. See A.1 Lexical structure for the
exact lexical states where pragmas are recognized. A must-understand
extension is identified by its ExtensionQName.

If an implementation does not support a must-understand extension, then a
static error is raised. If an implementation does support an
must-understand extension and the implementation determines that the
ExtensionContents are invalid, then a static error is raised. Otherwise,
the effect of the must-understand extension on the result of the Query
being executed is implementation-defined.

The following example shows how a must-understand extension might be used:

   declare namespace exq = "http://example.org/XQueryImplementation"

   for $e in doc("employees.xml")//employee
   order by $e/lastname (:: extension exq:RightToLeft ::)
   return $e

An implementation that supports the exq:RightToLeft must-understand
extension might order the last names by examining characters from right to
left instead of left to right. An implementation that did not support this
must-understand extension would raise a static error.


2.5.5.3 Semantic Extensions

An implementation may extend XQuery by supporting semantic extensions. A
semantic extension allows a conforming Query to be processed in a
non-conforming way. The way in which such semantic extensions are enabled
is implementation-defined.

The effect of a semantic extension on the result of a Query is
implementation-defined.

The following example shows how a command line might be used to enable a
semantic extension:

   xquery q12.xquery
   98

   xquery q12.xquery -EmptyIdentity=on
   100

The execution of the query contained in q12.xquery might treat an empty
sequence as 0 when it is being used in addition and subtraction and treat
it as 1 when it is being used in multiplication and division.


2.5.5.4 XQuery Flagger

An XQuery Flagger is a facility that is provided by an implementation that
is able to identify queries that contain extensions other than pragmas. If
an implementation supports extensions other than pragmas, then an XQuery
Flagger must be provided. The XQuery Flagger is disabled by default; the
mechanism by which the XQuery Flagger is enabled is implementation-defined.
When enabled, the XQuery Flagger will raise a static error for an otherwise
valid Query that contains either must-understand extensions or semantic
extensions.

An XQuery Flagger is provided to assist programmers in producing queries
that are portable among multiple conforming XQuery implementations.

The following examples show how an XQuery Flagger might be used:

   xquery q10.xquery
   <employee> ... </employee>

   xquery q10.xquery -Flagger=on
   [static error] A must-understand extension is being used:
   exq:RightToLeft

   xquery q12.xquery -EmptyIdentity=on
   100

   xquery q12.xquery -EmptyIdentity=on -Flagger=on
   [static error] A semantic extension is being used: EmptyIdentity

Updates to proposal:

- Usage of (:: ::) syntax.

- must-understand extension.

Actual Resolution

Decision by: xquery on 2003-03-12 ([link to member only information] )

#1 PRAGMAS: Adopted Unanimously.

#2 MUST-UNDERSTAND EXTENSIONS: Adopted.

#3 SEMANTIC EXTENSIONS: Rejected.

#4 FLAGGER: Adopted.

318. sort-in-FLWR: Add 'order by' clause to FLWR?

Locus: xquery Cluster: sort Priority: 1 Status: decided
Originator: Jonathan Robie
Add 'order by' clause to FLWR?

Description

Four issues were raised in a proposal to restructure sorting in XQuery [1]:

1. Should we add an 'order by' clause to FLWR?

The following syntax has been proposed:

FLWRExpr ::= (ForClause |  LetClause)+ SortClause? WhereClause?
"return"  Expr
OrderClause ::=  "order by" stable? SortSpecList
SortSpecList ::= Expr SortModifier ("," SortSpecList)?
SortModifier ::= ("ascending" |  "descending")? ("empty" "greatest"
|  "empty" "least")?

The OrderClause sorts the tuple stream based on the conditions specified in the SortSpecList.

In the status quo, 'sortby' is a standalone postfix expression. FLWR is used to iterate, and 'sortby' is used to sort. This causes certain difficulties, because iteration and sorting are not distinct, unrelated operations - in general, the order in which the output sequence is ordered determines the best order to choose when iterating over the input.

When sorting data created with element constructors, it can sometimes be quite tricky to determine the original source of data in a constructed element. The more complex the expressions that construct the element, the more tricky this becomes. It is also tricky to iterate in an order determined by data that is not returned in a generated sequence.

If we add this clause, should a FLWOR expression that contains an OrderClause but no ForClause result in a semantic error, since there is no tuple stream to sort?

2. If we add an 'order by' clause, should we keep the sortby() expression, or remove it from our language?

Keeping it is convenient for some expressions. Removing it leaves us with a simpler language, and does not require us to explain to our users why we have two ways of doing the same thing.

3. How should we formalize 'order by' - or should we formalize it in Version 1.0?

The most straightforward way to formalize 'order by' is to use tuples, which do not exist in our Data Model, and these would cause significant change to our Formal Semantics. However, the semantics of 'order by' are straightforward.

Our options seem to be:

3.a. Ensure that we know how it would be formalized using tuples, but postpone including this in the Formal Semantics until after Version 1.

3.b. Refuse to add the feature unless it can be formalized with our current Data Model.

3.c. Restrict the feature to functionality easily formalized with our current Data Model.

I believe there was significant enthusiasm for 3.a. in today's telcon.

4. Is the 'order by' clause part of the XPath spec, or is it only in XQuery?

Jonathan

[1] http://lists.w3.org/Archives/Member/w3c-xsl-query/2002Jul/0177.html

Interactions and Input

Actual Resolution

Decision by: xpath-tf on 2002-10-16 ([link to member only information] )

'order by' has been added.

319. namespace-definitions-and-validate: Namespace definitions and in-scope namespaces

Locus: xquery Cluster: namespaces Priority: 1 Status: active
Originator: XPath TF
Namespace definitions and in-scope namespaces

Description

Addition of namespaces in the query prolog to the in-scope namespaces; how is this information carried through to provide input to validation?

Additional aspecs are:

(a) the whole question of how the namesapce context is affected by namespace declarations in element constructors

(b) the general notion (in XQuery, specifically), that the static context can vary for different parts of a query

(c) what information gets through to act as input to validation

320. types-conformancelevels-same-results: Should different conformance levels give the same result for the same query and data?

Issue Class: T Locus: xquery Cluster: types Priority: 1 Status: decided
Originator: Anders Berglund
Should different conformance levels give the same result for the same query and data?

Description

Are different conformance levels going to give the same results? Is it possible to get different results for the same query? The principle should be that you either get the same result or a failure. Currently this isn't the case.

Interactions and Input

[link to member only information] Anders Berglund:

[link to member only information] Kristoffer Rose:

Actual Resolution

Decision by: proc-mod-tf on 2003-02-11 ([link to member only information] )

Decision by: xquery on 2003-02-19 ([link to member only information] )

Given that types add semantics, there is no way to achieve the proposed principle between basic XQuery and schema import without adding additional specification in the query.

It is decided not to add any such functionality and close this issue without action.

321. validate-lax-strict: Is validate strict or lax?

Locus: xquery Cluster: validate Priority: 1 Status: decided
Originator: XSL/XQuery joint
Is validate strict or lax?

Description

Does "validate" do strict or lax validation?

Actual Resolution

Decision by: xquery on 2002-12-18 ([link to member only information] )

Decision to accept the propsal of Phil Wadler in http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0378.html.

322. validate-lax-strict-override: "validate" strict/lax override?

Locus: xquery Cluster: validate Priority: 1 Status: decided
Originator: XSL/XQuery joint
"validate" strict/lax override?

Description

Should the user should be able to override which type (strict/lax) of validation "validate" does?

Actual Resolution

Decision by: xquery on 2002-12-18 ([link to member only information] )

Decision to accept the propsal of Phil Wadler in http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0378.html.

325. element-def-not-in-in-scope: Refering to element that is not in the in-scope schema def.

Issue Class: T Locus: xpath Cluster: types Priority: 1 Status: decided
Originator: XQuery
Refering to element that is not in the in-scope schema def.

Description

In recent discussions on the type system and when reviewing the documents I noticed that many people interpret

element foo

differently than the spec indicates it needs to be interpreted. This seems to indicate that we have a problem.

The semantics that people expect seems to be:

element foo is the same as element foo of type xs:anyType and matches all elements with the given name (regardless where or whether the element was declared in the schema).

attribute foo is the same as attribute foo of type xs:anySimpleType and matches all attributes with the given name regardless where or whether it was declared in the schema).

However our spec [1] says:

Another form of ElemOrAttrType is simply a QName, which is interpreted as the required name of the element or attribute. The QName must be an element or attribute name that is found in the in-scope schema definitions. The match is successful only if the given element or attribute has the required name and also conforms to the schema definition for the required name. This can be verified in either of the following ways:

If the schema definition for the required name has a named type, the given element or attribute must have a type annotation that is the same as that named type or is known (in the in-scope schema definitions) to be derived from that named type. For example, suppose that a schema declares the element named location to have the type State. Then the SequenceType element location will match a given element only if its name is location and its type annotation is State or some named type that is derived from State.

If the schema definition for the required name has an anonymous (unnamed) type definition, the actual content of the given element or attribute must structurally comply with this type definition. For example, suppose that a schema declares the element named shippingAddress to have an anonymous complex type consisting of a street element followed by a city element. Then the SequenceType element shippingAddress will match a given element only if its name is shippingAddress and its content is a street element followed by a city element.

The constraint that an element must have a required name is considered to be satisfied if the element has been validated and found to be a member of a substitution group whose head element has the required name. Substitution groups are described in [XML Schema].

which seems to indicate that this is not the case.

I would like to open an issue on this. I think even if people do not want to use schema types, they may still want to restrict the argument type of a function to an element with a given name.

In addition, many people are surprised to see the SchemaContext in the SequenceType production for other usages than for validate in ...

While there is a use case, I wonder whether this needs to be a required feature for XQuery V1 given the leap in complexity. Maybe it would be useful to solve the above problem by saying that you have to use

element foo in /

to force the name to be in the in-scope schema definition? This would mean that / becomes allowed in the SchemaGlobalContext production.

Actual Resolution

Decision by: xpath-tf on 2002-12-17 ([link to member only information] )

Decision by: xquery on 2002-12-19 ([link to member only information] )Joint F2F

Decision by: xsl on 2002-12-19 ([link to member only information] )Joint F2F

In sequence type it is an error, it is valid in a path expression.

327. functions-parameter-evaluation: Evaluate unused function parameters?

Locus: xpath Cluster: functions Priority: 1 Status: decided
Originator: XSL/XQuery joint
Evaluate unused function parameters?

Description

Is an implementation obligated to evaluate all its parameters (and raise any errors doing so) even when they're not needed in the function body?

Actual Resolution

Decision by: xpath-tf on 2002-10-29 ([link to member only information] )as part of Agendum 1.

There is no need to evaluate "non needed" expressions.

Decision by: xquery on 2002-10-30 ([link to member only information] )accepting text for next publication, but keep issue active.

Decision by: xsl on 2002-10-31 ([link to member only information] )accepting text for next publication, but keep issue active.

Decision by: xpath-tf on 2003-03-18 ([link to member only information] )

No adverse public comments received. Close issue with no change.

328. cdata-section: What does CDATA section constructor construct?

Locus: xquery Cluster: cdata section Priority: 1 Status: decided
Originator: Michael Kay
What does CDATA section constructor construct?

Description

Section 3.7.5 describes CDATA section constructor, but these cannot be represented in the data model.

Actual Resolution

Decision by: xquery on 2002-12-11 ([link to member only information] )

Decided to close, with document changes as described by Mike Kay in http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0095.html, including editorial comments.

329. duplicate-attribute-constructors: Duplicate attribute constructors

Locus: xquery Cluster: constructors Priority: 1 Status: decided
Originator: Michael Kay
Duplicate attribute constructors

Description

If there are multiple constructors for the same attribute on an element; which one is taken or is it an error?

Actual Resolution

Decision by: xquery on 2002-12-11 ([link to member only information] )

Decided to make it an error for an element constructor to specify two attributes with the same name. Error to be documented in XQuery Section 3.7.4.1.

334. xquery-failed-validation: How are documents for which validation has failed processed?

Issue Class: T Locus: xpath Cluster: type-semantics Priority: 1 Status: decided
Originator: Jonathan Robie
How are documents for which validation has failed processed?

Description

What is the result of a failed validation? Can you inspect the result to detect this? Do you just get anySimpleType and anyType?

Interactions and Input

Actual Resolution

Decision by: xpath-tf on 2003-03-04 ([link to member only information] )

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

Access to documents that fail validation is not supported.

335. semantics-interfering-with-optimization: XPath/XQuery's current semantics greatly interferes with optimization

Locus: xpath Cluster: formal-semantics Priority: 1 Status: decided
Originator: Michael Rys
XPath/XQuery's current semantics greatly interferes with optimization

Description

Current semantics basically defines the semantics by mapping FLWRs and path expression to go top-down. Errors are normative. Problem is that we can not apply many optimizations. Simple query rewrites such as pushing or pulling filters, etc. Like to be able to push predicates down and evaluate them. Potentially the predicate might raise an error you would not have gotten if you processed top down. Want to allow implementations to do bottom up evaluations.

Suggested resolution:

The formal semantics defines dynamic evaluation in terms of a naive, top-down reduction of a core expression to a data-model value. Implementations may choose alternative evaluation strategies, which, for example, may reduce a core expression bottom-up. If an evaluation of a core expression yields a value (i.e., it does not raise an error), the value must be the same value as would be produced by the dynamic semantics defined in this document. The evaluation of a core expression may raise an error that may not be raised by the dynamic semantics as defined in this document.

Actual Resolution

Decision by: xpath-tf on 2002-10-29 ([link to member only information] )as part of Agendum 1.

Expressions, with the exception of "if", may be reordered and thus some errors may be raised that using another evaluation strategy may not have occurred.

Decision by: xquery on 2002-10-30 ([link to member only information] )accepting text for next publication, but keep issue active.

Decision by: xsl on 2002-10-31 ([link to member only information] )accepting text for next publication, but keep issue active.

Decision by: xpath-tf on 2003-03-18 ([link to member only information] )

No adverse public comments received. Close issue with no change.

338. whitespace-character-reference: Handling of whitespace and character references

Locus: xquery Cluster: whitespace Priority: 1 Status: decided
Originator: Michael Kay
Handling of whitespace and character references

Description

The effect of CharRef in Element or Attribute content is underspecified. For example, if the value of the CharRef is whitespace, does it behave like whitespace in Element or Attribute content, or does it behave like ordinary characters? Either way, it is hard to make it behave exactly like the XML construct that it mimics: in XML, a character reference such as suppresses certain effects such as whitespace normalization. It is not clear whether such normalization happens in XQuery.

Interactions and Input

Actual Resolution

Decision by: xquery on 2002-12-04 ([link to member only information] )

Confirmed that Mary's proposal for whitespace, that was accepted 2002-11-27, closes this issue.

Decision by: xquery on 2002-12-11 ([link to member only information] )

Resolved by the recent adoption of the revised text on attribute constructors.

339. element-attribute-construction-order: Error type for attributes constructed too late

Locus: xquery Cluster: errors Priority: 2 Status: decided
Originator: Don Chamberlin
Error type for attributes constructed too late

Description

What kind of error should be raised by an element constructor in which an attribute is encountered after other element content?

Actual Resolution

Decision by: xquery on 2002-12-11 ([link to member only information] )

This a type error. Type error to be documented in XQuery Section 3.7.2.

340. errors-unique-identification: How to identify errors?

Locus: xpath Cluster: errors Priority: 1 Status: decided
Originator: XPath TF
How to identify errors?

Description

How should we allocate codes or identifiers to errors defined in the spec? We should not use "explanatory sentences" as these are not appropriate for I18N reasons.

Actual Resolution

Decision by: xpath-tf on 2002-12-17 ([link to member only information] )

Decision by: xquery on 2002-12-19 ([link to member only information] )Joint F2F

Decision by: xsl on 2002-12-19 ([link to member only information] )Joint F2F

(not really an issue); Ashok and Norm will investigate whether we can editorially markup errors consistently.

Decision by: xpath-tf on 2003-01-07 ([link to member only information] )

Issue should remain open pending proposal on: ACTION XPATH-091-11 Mary adds herself to XPATH-091-11.

Decision by: xpath-tf on 2003-04-08 ([link to member only information] )

1. All occurrences of static and dynamic errors should be identified in the F&O, DM, language, and FS specs using distinguished error markup.

2. Error markup should include unique alpha-numeric identifier for each error which permits the source to refer to unique error definitions and to include reverse indices on errors.

3. In first cut, alpha-numeric error codes will not be revealed in printed documents, but we can reveal them at a later time if we decide to make error codes part of conformance requirements.

4. Until we consider an API for conveying errors to the evaluation environment, we recommend *not* requiring implementations to return specific error codes (and possibly additional context info such as location of error in query body or name of built-in function, etc.)

341. SequenceType-problems: Problems with SequenceType

Locus: xpath Cluster: syntax Priority: 1 Status: decided
Originator: Michael Kay
Problems with SequenceType

Description

Using the "instance of SequenceType" construct within a predicate of a path expression, or in an XSLT match pattern, is very unwieldy: the verbose English-like syntax of a SequenceType does not go well with the terse syntax of path expressions, leading to inelegant constructs like

select="//*[.instance of element of type address]"

Interactions and Input

[link to member only information] Michael Kay:

Proposed Resolution

1. Motivation

Many people have asked for the ability to test for elements of a given
type in path expressions, and to be able to write path expressions
that would retrieve nodes with types that match the declared types of
function parameters. For instance, consider the following query in the
syntax of our current Working Draft:

       define function name($e as element person)
         returns element name
       {
            $e/name
       }

       for $p in input()//person
       return name($p)

This query can fail at runtime, because the path expression matches
any element named person, and the function parameter requires a valid
element conforming to a globally declared element named person.

This proposal adds ElementType and AttributeType nodetests to path
expressions, and aligns the syntax of SequenceType with the syntax of
type tests done in path expressions. For instance, in the following
syntax, the KindTest "element(person)" matches only person elements
that are valid instances of the globally declared person element, and
the same test is used for the function's parameter type:

       define function name($e as element(person))
         returns element name
       {
            $e/name
       }

       for $p in input()//element(person)
       return name($p)

Using the same syntax and semantics for these tests in both path
expressions and SequenceType ensures that they are well aligned, and
reduces the number of expressions users of the language must learn. In
addition, it allows us to fix some problems with SequenceType that
have made the grammar complex to maintain.

ElementType and AttributeType nodetests also allow the names of types
to be used to select nodes, eg:

       define function name($e as element(person, surgeon))
         returns element name
       {
            $e/name
       }


       for $p in input()//element(person, surgeon)
       return name($p)

Or:

      for $date in input()//element(*, xs:date)
      return <date>{ $date }</date>

Note that the above queries provide enough type information to be
statically valid without 'treat as'. If a NameTest were used instead
of the ElementType nodetest, the above query would not be statically
valid, and the query writer would need to use treat as to make it so.

Using this proposal, the most convenient way to match locally declared
types in a path expression is to use the globally declared types in
which they are contained to establish a type context; eg, the
following query from use case STRONG is statically valid as modified
below:


define function names-match(
    $s as element(ipo:purchaseOrder/ipo:shipTo),
    $b as element(ipo:purchaseOrder/ipo:billTo)
    as xs:boolean
{
        $s/ipo:name = $b/ipo:name
}

for $p in document("ipo.xml")//element(ipo:purchaseOrder)
where not( names-match( $p/ipo:shipTo, $p/ipo:billTo ) )
return $p


ElementType and AttributeType nodetests can also be used in match
patterns on XSLT stylesheets, eg:

     <xsl:template match="element(person)">

     <xsl:template match="attribute(*,xs:date)">

For more examples of ElementType and AttributeType nodetests in match
patterns, see [1].

This proposal steals liberally from proposals by Phil Wadler, Jeni
Tennison, Michael Rys, and Mike Kay. Don Chamberlin gave detailed
review and pointed out important problems and their solutions.  Scott
Boag tested the grammar.


========================================================================
2. Examples of ElementTypeTest and AttributeTypeTest

Informally, the principles for matching an ElementTypeTest or
AttributeTypeTest are as follows:

- element() matches elements, attribute() matches attributes.

- names in ElementTypeTest and AttributeTypeTest test the name of a
   node. If the name of an element identifies a Corresponding Element
   Declaration which is the head of a substitution group, the name of
   an ElementTypeTest also matches other names in the substitution
   group.

- types in ElementTypeTest and AttributeTypeTest match type
   annotations.  If no type is supplied, there must be a Corresponding
   Element Declaration or a Corresponding Attribute Declaration, which
   is used to nominate a type.

The following examples illustrate these semantics by stating what
nodes an ElementTypeTest would match.

  element()
  element(*)
  element(*,*)

    Matches any element. These three forms are equivalent.

  element( person )

    Matches any element named 'person' with the type corresponding to
    the globally declared 'person' element; if this element is
    nillable, also matches any empty element named person containing an
    xsi:nil attribute with the value 'true'. If the globally declared
    'person' element is the head of a substitution group, also matches
    element names from the substitution group. If there is no globally
    declared 'person' element, a type error is raised.

  element( person, * )

    Matches any element named person or any element whose name is in
    the substitution group of the globally declared element person, if
    one exists. This is equivalent to the earlier ~person syntax, which
    we feel is no longer needed.

  element( person, personType nillable )

    Matches any element named 'person' with the type 'personType',
    including any empty element named person containing an xsi:nil
    attribute with the value 'true'. If the globally declared 'person'
    element is the head of a substitution group, also matches element
    names from the substitution group.

  element( *, xs:integer nillable )

   Matches any element of type xs:integer, including any such element
   with xs:nil="true" and no content.

  element( foo/bar/person )

    Matches any element named 'person' with the type of the
    corresponding element declaration.

  element( foo/bar/person, personType )

    Syntax Error.

  attribute()

    Matches any attribute.

  attribute( foo/bar/person/@id )

    Matches any attribute named 'id' with the type of the corresponding
    attribute declaration.

  element( @*, xs:integer )

   Matches any attribute of type xs:integer.

  attribute( @price, xs:integer )

   Matches any attribute named price of type xs:integer.


========================================================================
3. Syntax


Tokens

Scott currently has the following as tokens, and is working on making
them productions:

[22]    SchemaGlobalContext    ::=    QName |  ("type" "(" QName ")")
[23]    SchemaContextStep    ::=    QName

Productions

[112]    SequenceType    ::=    (SequenceSingleType OccurrenceIndicator?)
                              |  <"empty" "(" ")">
[113]    SequenceSingleType    ::=    AtomicType |  ItemType
[114]    AtomicType    ::=    QName
[115]    ItemType    ::=   KindTest |  <"item" "(" ")">
[116]    KindTest    ::=   DocumentTest
                         |  ElementTypeTest
                         |  AttributeTypeTest
                         |  ProcessingInstructionTest
                         |  CommentTest
                         |  TextTest
                         |  AnyKindTest


[117]    DocumentTest    ::=    <"document" "(" ")">
[118]    ElementTypeTest ::=    <"element" "("> ((SchemaContextPath LocalName)
                             |  (NodeName ("," TypeName "nillable"?)?))? ")"
[119]    AttributeTypeTest ::=  <"attribute" "("> ((SchemaContextPath "@"
LocalName)
                             |  ("@" NodeName ("," TypeName)?))? ")"
[120]    SchemaContextPath ::=  <SchemaGlobalContext "/">
<SchemaContextStep "/">*
[122]    LocalName    ::=    QName
[123]    NodeName    ::=    QName |  "*"
[124]    TypeName    ::=    QName |  "*"
[125]    OccurrenceIndicator    ::=    "*" |  "+" |  "?"


========================================================================
4. Semantics

A ContextName identifies a valid path from a globally declared element
declaration or type definition in the in-scope schema definitions. For
instance, the following indicates a shipTo element on a purchaseOrder:

   purchaseOrder/shipTo

If a ContextName begins with type(t), then the path starts with a
global named type in the in-scope schema definitions. For instance,
the following indicates a shipTo element in a complex type called
purchaseOrderType:

   type(purchaseOrderType)/shipTo

The rules for matching an ElementTypeTest depend on the Corresponding
Element Declaration, which is determined as follows:

   An ElementName is the first argument of an ElementTypeTest.

   If the ElementName has the form NodeName, and it matches the name of
   a globally declared element declaration in the in-scope schema
   definitions, it is the "Corresponding Element Declaration". If the
   ElementName has the form SchemaContextPath LocalName, then the
   element declaration which would correspond to an element named
   LocalName in the given context is the "Corresponding Element
   Declaration".

The rules for matching an AttributeTypeTest depend on the
Corresponding Attribute Declaration,

   An AttributeName is the first argument of an AttributeTypeTest.

   If the AttributeName has the form NodeName, and it matches the name
   of a globally declared element declaration in the in-scope schema
   definitions, it is the "Corresponding Element Declaration". If the
   AttributeName has the form SchemaContextPath LocalName, then the
   element declaration which would correspond to an element named
   LocalName in the given context is the "Corresponding Attribute
   Declaration".

An ElementTypeTest matches a node if the node is an element, the
element's name matches the ElementName of the ElementTypeTest, and the
element's type matches the type and nillability of the
ElementTypeTest.

An ElementName is matched as follows:

   If the ElementName is absent or "*", it matches an
   element of any name.

   If the ElementName has the form NodeName, it matches an element if
   the expanded-QNames of the element and the ElementName match. If the
   ElementName has the form SchemaContextPath LocalName, it matches an
   element if the expanded-QNames of the element and the LocalName
   match.

   If the Corresponding Element Declaration is the head of a
   substitution group, then the ElementName also matches an element if
   the expanded-QNames of the element and any element in the
   substitution group match.

   Otherwise, the ElementName does not match the element's name.

An element's TypeName is matched as follows:

   If the TypeName is "*", it matches an element of any type.

   If the TypeName is absent, then the default TypeName is selected,
   which is the type of the Corresponding Element Declaration. The
   default nillability is also selected, which is the nillability of
   the Corresponding Element Declaration.

   If the expanded-QName of the TypeName matches the element's type or
   any of its subtypes, then the TypeName matches the element's type if
   the type nillability is also satisfied.

   If the element's type name is an anonymous local type, the TypeName
   must be a default type chosen from the Corresponding Element
   Declaration, and they match if the element's type is the same as or
   derived by restriction or extension from the type of the TypeName,
   provided the type nillability is also satisfied.

   An element's type nillability is not satisified when the type is not
   nillable, and the element's dm:nil property is 'true'; otherwise, it
   is satisfied.

The semantics of AttributeTypeTest are parallel, substituting the word
'attribute' for 'element' in the above description and eliminating
substitution groups and nillable, which do not apply to attributes. An
AttributeTypeTest matches a node if the node is an attribute, the
attribute's name matches the AttributeName of the AttributeTypeTest, and
the attribute's type matches the type and nillability of the
AttributeTypeTest.


An AttributeName is matched as follows:

   If the AttributeName is absent or "*", it matches any attribute.

   If the AttributeName has the form NodeName, it matches an element if
   the expanded-QNames of the element and the AttributeName match. If
   the AttributeName has the form SchemaContextPath LocalName, it
   matches an element if the expanded-QNames of the element and the
   LocalName match.

   Otherwise, the AttributeName does not match the attribute's name.

An attribute's TypeName is matched as follows:

   If the TypeName is "*", it matches an attribute of any type.

   If the TypeName is absent, then the default TypeName is selected,
   which is the type of the corresponding attribute declaration.

   If the expanded-QName of the TypeName matches the attribute's type
   or any of its subtypes, then the TypeName matches the attribute.

   If the attribute's type name is an anonymous local type, the
   TypeName must be a default type chosen from the Corresponding
   Attribute Declaration, and they match if the attribute's type is the
   same as or derived by restriction or extension from the type of the
   TypeName.


========================================================================
6. attribute() and default axes

To allow attribute() to be used in path expressions, abbreviated steps
need to be modified as follows:

Current text:


   >     The most important abbreviation is that child:: can be omitted
   >     from a step. In effect, child is the default axis. For example,
   >     a path expression section/para is short for
   >     child::section/child::para.


Proposed text:


   >     The most important abbreviation is that child:: can be omitted
   >     from a step, or attribute:: can be omitted from a step that
   >     contains an AttributeTypeTest. In most cases, child is the
   >     default axis. For example, a path expression section/para is
   >     short for child::section/child::para. However, if the step
   >     contains an AttributeType, the default axis is attribute::. For
   >     example, child::section/attribute( id ) is short for
   >     child::section/attribute::attribute( id ).



========================================================================
7. Static Semantics

    To be supplied.


========================================================================
8. Issues

Issue:

     Should a WildCard be allowed for the names of attributes and
     elements? For instance, one might imagine wanting to select only
     HTML elements of type xs:string:

         element(html:*, xs:string)

Actual Resolution

Decision by: xpath-tf on 2003-03-04 ([link to member only information] )

Decision by: xsl on 2003-03-06 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-06 ([link to member only information] )Joint meeting

Proposal accepted resolving issue.

343. namespaces-functions: Do functions in the null namespace clash with functions in the default namespace?

Locus: xpath Cluster: namespaces Priority: 1 Status: active
Originator: XPath TF
Do functions in the null namespace clash with functions in the default namespace?

Description

If you define the DFN (default function namespace) to be the null namespace, which you must do if you are going to call functions in this namespace, can you still use unprefixed names to refer to functions in the built-in namespace?

Interactions and Input

Actual Resolution

Decision by: xquery on 2003-01-22 ([link to member only information] )A static error is raised when there is a clash between a user-defined function in the default namespace and any other function of the same name in the default namespace.

437. FS-Issue-0094: Static type errors and warnings

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Don Chamberlin
Static type errors and warnings

Description

Static type errors and warnings are not specified. We need to enumerate in both the [XPath/XQuery] and formal semantics documents what kinds of static type errors and warnings are produced by the type system. See also [resolved issue #FS-Issue-0090].

Actual Resolution

Decision by: fs-editors on 2003-01-12 ([link to member only information] )

Dec. FS working draft describes the semantics of errors.

441. FS-Issue-0098: Implementation of and conformance levels for static type checking

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Don Chamberlin
Implementation of and conformance levels for static type checking

Description

This issue is related to [resolved issue #FS-Issue-0059] Static type checking may be difficult and/or expensive to implement. Some discussion of algorithmic issues of type checking are needed. In addition, we may want to define "conformance levels" for [XPath/XQuery], in which some processors (or some processing modes) are more permissive about types. This would allow [XPath/XQuery] implementations that do not understand all of Schema, and it would allow customers some control over the cost/benefit tradeoff of type checking.

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Close issue 441 with no further work.

443. FS-Issue-0100: Namespace resolution

Locus: formal-semantics Cluster: Semantics? Priority: 1 Status: active
Originator: FS Editors
Namespace resolution

Description

The way (when? where?) namespace prefixes are resolved is still an open issue.

444. FS-Issue-0101: Support for mixed content in the type system

Locus: formal-semantics Cluster: Priority: 1 Status: decided
Originator: FS Editors
Support for mixed content in the type system

Description

Support for mixed content in the type system is an open issue. This reopens issue [resolved issue #FS-Issue-0016]. Dealing with mixed content with interleaving raises complexity issue. See also #FS-Issue-0103.

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

The formal semantics is a specification of the behavior of an XQuery processor, not a recipe for implementation. The uses of interleaving in the specification are sufficiently restricted that a practical implementation can be written.

446. FS-Issue-0103: Complexity of interleaving

Locus: formal-semantics Cluster: Typing Priority: 1 Status: decided
Originator: FS Editors
Complexity of interleaving

Description

The current type system allows interleaving is allowed on arbitrary types. Interleaving is an expensive operation and it is not clear how to define subtyping for it. Should we restrict use of interleaving on (optional) atomic types ? Should this restriction reflects the one in XML schema ? Related to [resolved issue #FS-Issue-0077].

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

The formal semantics is a specification of the behavior of an XQuery processor, not a recipe for implementation. The uses of interleaving in the specification are sufficiently restricted that a practical implementation can be written.

449. FS-Issue-0106: Constraint on attribute and element content models

Locus: formal-semantics Cluster: Typing Priority: 1 Status: decided
Originator: Jerome
Constraint on attribute and element content models

Description

The [XPath/XQuery] type system allows more content model than what XML Schema allows. For instance, the current type grammar allows the following types:

   element d { (attribute a | element b, attribute c)* }
   attribute a { element b }

Section #FS-sec_types indicates corresponding constraints on the [XPath/XQuery] type system to avoid that problem. The status of these constraints is unclear. When are they enforced and checked?

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

Closed following the semantics of element constructors agreed at the December f2f meeting.

450. FS-Issue-0107: Semantics of data()

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: FS Editors
Semantics of data()

Description

What is the semantics of data() applied to anything else than an element or attribute node ?

Proposed Resolution

XQuery 1.0 and XPath 2.0 Data Model
W3C Working Draft 17 January 2003
http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Jan/0251.html

4.1.5 string-value Accessor
----------------------------

1. REPLACE entire section WITH:

    Every node has a string value; the way in which the string value
    is computed is different for each kind of node and is specified in
    the sections on nodes below.

4.1.6 typed-value Accessor
--------------------------

1. REPLACE:
      Otherwise, xs:anyType for elements or xs:anySimpleType for
attributes.

   WITH:
      Otherwise, xs:anyType for elements or xdt:untypedAtomic for
attributes.

2. REPLACE :

    * If the item is an element node with type xs:anyType, then its
      typed value is equal to its string value, as an instance of
      xdt:untypedAtomic.

  WITH:

    * If the node is an element node with type xs:anyType, then its
      typed value is equal to its string value, as an instance of
      xdt:untypedAtomic.

3. REPLACE :

    * The typed value of an element node with a simple type is derived
      from its string value and type in a way that is consistent with
      XML Schema validation.

  WITH:

    * If the node is an element node with a simple type or with a
      complex type of simple content, then its typed value is
      derived from its string value and type in a way that is
      consistent with XML Schema validation.

4. ADD:

    * If the item is an element node with complex type of empty
      content, then its typed value is the empty sequence.

    * If the node is an element node with a complex type of mixed
      content, then its typed value is its string value as an instance
      of xdt:untypedAtomic.

5. REPLACE:

    * If the item is an element node with complex content,
      dm:typed-value returns the empty sequence.

  WITH:

    * If the item is an element node with complex type of complex
      content, then its typed value is the empty sequence.

*************************************************
XQuery 1.0 and XPath 2.0 Functions and Operators
W3C Working Draft 10 December 2002
http://lists.w3.org/Archives/Member/w3c-archive/2002Dec/att-0035/02-xquery-operators.html

2.4 fn:data
-----------

1. REWRITE entire section as described in:
   http://lists.w3.org/Archives/Member/w3c-xsl-query/2002Nov/0391.html

This text incorporates changes for nodes with complex type of mixed
content:

  fn:data($srcval as item*) as atomic value*

  The fn:data function takes a sequence of items and returns a
  sequence of atomic values.

  The result of fn:data is the sequence of atomic values produced by
  applying the following rules to each item in $srcval:

    If the item is an atomic value, it is returned.

    If the item is a node, fn:data returns the typed value of the
    node, as defined by the accessor function dm:typed-value defined
    for that kind of node in [XQuery 1.0 and XPath 2.0 Data Model].

    If the item is a comment, document, namespace,
    processing-instruction, or text node, then its typed value is
    equal to its string value, as an instance of xdt:untypedAtomic.

    If the item is an attribute node with type annotation
    xs:anySimpleType, then its typed value is equal to its string
    value, as an instance of xdt:untypedAtomic. The typed value of any
    other attribute node is derived from its string value and type
    annotation in a way that is consistent with XML Schema validation,
    as described in [XQuery 1.0 and XPath 2.0 Data Model].

    If the item is an element node whose type annotation
    denotes a complex type of empty content, then its typed value
    is equal to the empty sequence.

    If the item is an element node whose type annotation is xs:anyType
    or denotes a complex type of mixed content, then its typed value
    is equal to its string value, as an instance of xs:untypedAtomic.

    If the item is an element node whose type annotation denotes a
    simple type or a complex type of simple content, then its typed
    value is derived from its string value and type in a way that is
    consistent with XML Schema validation, as described in [XQuery 1.0
    and XPath 2.0 Data Model].

    If the item is an element node whose type annotation denotes a
    complex type with complex content (i.e., a type that permits
    subelements), fn:data raises a type error.

    [ Ed note: The typed-value accessor returns an empty sequence when
      applied to an element node with complex type of comple content,
      whereas fn:data() raises a type error, because type errors are a
      characteristic of the language, not the data model. ]

************************************************************************
XQuery 1.0: An XML Query Language
W3C Working Draft 15 November 2002
http://www.w3.org/TR/xquery/

and

XPath 2.0
W3C Working Draft 15 November 2002
http://www.w3.org/TR/xpath20/

2.3.2 Typed Value and String Value
----------------------------------

1. ADD definition of fn:data() as given above following:

  The typed value and string value for each kind of node are defined
  by the dm:typed-value and dm:string-value accessors in [XQuery 1.0
  and XPath 2.0 Data Model].

  The normative definitions are in the [XQuery 1.0 and XPath 2.0 Data
  Model] and is repeated here for convenience:

*****************************************************************************
XQuery 1.0 and XPath 2.0 Formal Semantics
W3C Working Draft 15 December 2002
http://lists.w3.org/Archives/Member/w3c-archive/2003Jan/0033.html

7.2.5 The fn:data function
--------------------------

1. This section is entirely rewritten to align with new semantics.

Introduction

  The fn:data function converts a sequence of items to a sequence of
  atomic values.

Notation

  Infering the type for the fn:data function is done by applying the
  fn:data function as a Filter, using the same approach as for the
  XPath steps.

    statEnv |- fn:data on Type1 : Type2

Static Type Analysis
--------------------

  The general rule for the function fn:data is to apply the filter
  [fn:data on] to the prime type of its argument type, then apply the
  quantifier to the result:

                 statEnv |- Expr : Type
          statEnv |- [fn:data on] prime(Type) : Type1
  ----------------------------------------------------
  statEnv |- fn:data(Expr) :  Type1 o quantifier(Type)


  The rules for the [fn:data on] filter always take a prime type
  (i.e., a union of item types) as an argument.

  When applied to none, [fn:data on] yields none.

    ---------------------------------
    statEnv |- [fn:data on] none : none


  When applied to the union of two types, [fn:data on] is applied to
each
  of the two types.  The resulting types are combined into a factored
  type.  This rule is necessary because [fn:data on] may return a
sequence
  of atomic types.


             statEnv |- [fn:data on] Type1 : Type3
             statEnv |- [fn:data on] Type2 : Type4
    ------------------------------------------------
    statEnv |- [fn:data on] Type1 | Type2 :
      prime(Type3 | Type4) o quantifier(Type3 | Type4)

  When applied to an atomic type, the [fn:data on] filter simply
  returns the atomic type:

                   Type <: xdt:anyAtomicType
               ---------------------------------
               statEnv |- [fn:data on] Type : Type

  When applied to comment, processing instruction, text, and document
  node types, the [fn:data on] filter returns xdt:untypedAtomic.

   Type <: comment | processing-instruction | text | document
  -----------------------------------------------------------
       statEnv |- [fn:data on] Type : xdt:untypedAtomic

  When applied to attribute node types with type annotation
  xs:anySimpleType or element node types with type annotation
  xs:anyType, the [fn:data on] filter returns xdt:untypedAtomic.

  statEnv |- AttributeType static lookup (of type xs:anySimpleType)
  -----------------------------------------------------------------
     statEnv |- [fn:data on] AttributeType : xdt:untypedAtomic

  statEnv |- ElementType static lookup (of type xs:anyType)
  -----------------------------------------------------------------
     statEnv |- [fn:data on] AttributeType : xdt:untypedAtomic

  When applied to an attribute type with any type annotation other
  than xs:anySimpleType, the [fn:data on] filter returns the attribute's
  simple type.

  statEnv |- AttributeType static lookup (of type TypeName)
             not(TypeName = xs:anySimpleType)
  statEnv |- (of type TypeName) expands to Type
  ----------------------------------------------------------
     statEnv |- [fn:data on] AttributeType : Type

  When applied to an element type whose type annotation denotes a
  simple type or a complex type of simple content or a complex type of
  empty content, the [fn:data on] filter returns the element's simple
  type.

     statEnv |- ElementType static lookup TypeReference
     statEnv |- TypeReference expands to Type
                 Type <: (Type1, Type2)
                 Type1 <: AttributeType*
                Type2 <: xs:anySimpleType
  ----------------------------------------------------------
          statEnv |- [fn:data on] ElementType : Type2

  When applied to an element type whose type annotation denotes a
  complex type of mixed content, the [fn:data on] filter returns
  xdt:untypedAtomic.

     statEnv |- ElementType static lookup (of type TypeName)
statEnv.typeDefn(TypeName) => define type TypeName Derivation? Mixed {
Type1? }
-------------------------------------------------------------------------------
        statEnv |- [fn:data on] ElementType : xdt:untypedAtomic

  The [fn:data on] filter is not defined on any element type whose
  type annotation denotes a complex type of complex content and
  therefore raises a static error.

Dynamic Evaluation
------------------

The dynamic semantics of fn:data() are specified in [2.4 fn:data] of
[XQuery 1.0 and XPath 2.0 Functions and Operators].

Actual Resolution

Decision by: xpath-tf on 2003-02-11 ([link to member only information] )

Decision by: xquery on 2003-02-19 ([link to member only information] )

Decision by: xsl on 2003-02-27 ([link to member only information] )

Proposal accepted.

452. FS-Issue-0109: Semantics of order by

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: active
Originator: Jerome
Semantics of order by

Description

The precise semantics of order by is still open issue.

453. FS-Issue-0110: Semantics of element and attribute constructors

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Jerome
Semantics of element and attribute constructors

Description

The precise semantics of element constructors is still an open issue.

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

Closed following the semantics of element constructors agreed at the December f2f meeting.

455. FS-Issue-0112: Typing for the "typeswitch" default clause

Locus: formal-semantics Cluster: Static typing Priority: 1 Status: decided
Originator: Jerome
Typing for the "typeswitch" default clause

Description

There is an asymetry in the typing for the default clause in typeswitch vs. the other case clauses. This results in a less precise type when the default clause can be applied.

It would be nicer to be able to have the type be more precise, like for the other case clauses.

The technical problem is the need for some form of negation. I think one could define a "non-common-primes" function that would do the trick, but I leave that as open for now until further review of the new typeswitch section is made.

Actual Resolution

Decision by: fs-editors on 2003-02-13 ([link to member only information] )

Decision by: xquery on 2003-02-19 ([link to member only information] )

Decision by: xsl on 2003-02-27 ([link to member only information] )

Accepting proposal in #FS-Issue-0173 resolves this issue.

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

Reaffirming decision.

457. FS-Issue-0114: Dynamic context for current date and time

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Jerome
Dynamic context for current date and time

Description

The following components dynamic contexts have no formal representation yet: current date and time.

Related question: where are these context components used?

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

Add current date and time in the Dynamic Environment.

458. FS-Issue-0115: What is in the default context?

Locus: formal-semantics Cluster: Language Priority: 1 Status: active
Originator: Jerome
What is in the default context?

Description

What do the default namespace and type environments contain? I believe at least the default namespace environment should contain the "xs", "fn" and "op" prefixes, as well as the default namespaces bound to the empty namespace. Should the default type environment contain wildcard types?

459. FS-Issue-0116: Serialization

Locus: formal-semantics Cluster: Language Priority: 1 Status: decided
Originator: Jerome
Serialization

Description

Serialization of data model instances, and XQuery results is still an open issue.

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

Serialization is implemented in the data model.

461. FS-Issue-0118: Data model syntax and literal values

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Phil Wadler
Data model syntax and literal values

Description

Phil suggests the data model should support primitive literals in their lexical form, in which case no explicit dynamic semantic rule would be necessary.

More generally, should the data model support a constructor syntax?

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

The corresponding syntax is going to be implemented in the formal semantics.

472. FS-Issue-0129: Static typing of union

Locus: formal-semantics Cluster: Static typing Priority: 1 Status: decided
Originator: Michael Rys
Static typing of union

Description

What should be the semantics of arithmetics expressions over unions. Right now, it would raise a dynamic error. Do we want to raise a static error?

Should operators and functions consistenly with respect to typing?

With the current semantics in Section 4.5 expr1 + expr2 raises a static type error if (e.g.) expr1 has type string and expr2 has type integer. It raises only a dynamic error, if expr1 has type (string | integer) and expr2 has type integer, and expr1 actually evaluates to a string. An alternative would be that this raises also a static error, because it cannot be guarantueed to succeed on all instances.

Proposed Resolution

For user-defined functions there is no issue and the current static typing rules work fine.

There is an issue about static typing for built-in overloaded functions (arithmetic and comparison operators). In that case, the following algorithm is proposed:

If one or both of the types of the operands are a union, static typing is performed for each par of item types in the union. If any of the cases raises a static type error, the whole static typing raises a static type error. Otherwise each resulting static type is unioned to form the final result type.

Here are examples for the expression (E1 + E2) in the case of various input types:

     E1 : int and E2 : int
then E1 + E2 : int

     E1 : float and E2 : int
then E1 + E2 : float

those cases did not change. In case there is a union:

     E1 : (float | int) and E2 : int
then E1 + E2 : (float | int)

since both cases (int + int) and (float | int) could occur.

E1 : (float | int) and E2 : (int | string)

raises a static error since (int + string) raises a static error.

Actual Resolution

Decision by: xquery on 2003-02-12 ([link to member only information] )

Proposal accepted.

473. FS-Issue-0130: When to process the query prolog

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: active
Originator: Jerome
When to process the query prolog

Description

The query prolog needs to be processed before the normalization phase. This is not reflected yet in the processing model.

475. FS-Issue-0132: Typing for descendant

Locus: formal-semantics Cluster: Static typing Priority: 1 Status: active
Originator: Peter Fankhauser
Typing for descendant

Description

The current static typing for descendant is still under review and the inferences rules in that version are probably containing bugs.

478. FS-Issue-0135: Semantics of special functions

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Michael Kay
Semantics of special functions

Description

The current semantics does not completely cover built-in functions. Some functions used in the Formal semantics, or some functions from the XQuery 1.0 and XPath 2.0 Functions and Operators document need additional semantics specification.

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

Ashok has posted a list of functions for which we need special typing rules: http://lists.w3.org/Archives/Member/w3c-query-editors/2003Feb/0027.html

It is now editorial just to implement those typing rules in the formal semantics document.

479. FS-Issue-0136: Non-determinism in the semantics

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Mary Fernandez
Non-determinism in the semantics

Description

Some operations, such as logical operations and quantified operations are not deterministics ("early-out" semantics allowing not to evaluate all of the expressions). The formal semantics cannot capture the non-determinism in those operations.

Actual Resolution

Decision by: fs-editors on 2003-01-12 ([link to member only information] )

Dec. FS working draft describes non deterministic semantics.

481. FS-Issue-0138: Semantics of Schema Context

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: active
Originator: Jerome Simeon
Semantics of Schema Context

Description

The semantics of Schema Context types in the SequenceType production is still an open issue.

482. FS-Issue-0139: Type equivalence rules

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Michael Rys
Type equivalence rules

Description

Should we add back equivalence rules for types (e.g., T1** == T1* or (T1 | T1) == T1). They are useful in practical implementations (e.g., to print an infered type or reduce complexity of infered types), and could be added in an appendix.

Actual Resolution

Decision by: xquery on 2003-02-12 ([link to member only information] )

Decided to add back equivalence rules.

484. FS-Issue-0141: Treatment of nillability and xsi:nil

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Michael Rys
Treatment of nillability and xsi:nil

Description

Nillability on an element declaration indicates that content of the corresponding element can be empty. The current data model preserves the xsi:nil attribute and this is used in the semantics at the type level. An alternative design would be to remove the xsi:nil attribute and add a 'nillable' marker in the schema component in the data model. This might be helping when we perform updates.

Actual Resolution

Decision by: xpath-tf on 2002-12-17 ([link to member only information] )

Guided by Jerome the following was decided:

Assume: an element of type T may be nillable. Another element of type T may not be nillable.

There is a Bug in language book re. type matching. Element with nil='true' does not have content according to the given type.

Question 1 - Yes 10 Abstain 1, Recorded No from Vassilis

Question 4 - Yes (unanimous) Do not know Vasillis votes.

Question 3 - nil marker in datamodel and keep xsi:nil (both) Votes:1, 0, 8 MRys abstains as he wants update case clarified.

Question 2 - Not relevant due to Yes answer to 4.

Decision by: xquery on 2002-12-19 ([link to member only information] )Joint F2F

Decision by: xsl on 2002-12-19 ([link to member only information] )Joint F2F

Decided to accept Jerome's proposal in http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0352.html.

486. FS-Issue-0143: Support for PI, comment and namespace nodes

Locus: formal-semantics Cluster: Typing Priority: 1 Status: active
Originator: FS Editors
Support for PI, comment and namespace nodes

Description

The [XPath/XQuery] type system does not currently support PI nodes, comment nodes and namespace nodes.

487. FS-Issue-0144: Representation of text nodes in formal values

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Jonathan Robie
Representation of text nodes in formal values

Description

Formal Values described in section #FS-sec_values represents either text nodes for well-formed documents or values for validated documents. Do we need to support a dual representation with both text nodes and values in the formal semantics?

Actual Resolution

Decision by: xsl on 2003-03-07 ([link to member only information] )Joint meeting

Decision by: xquery on 2003-03-07 ([link to member only information] )Joint meeting

The formal semantics will keep the current formalism for values which uses either atomic values or text, but not both. The current version is easier to read and understand.

488. FS-Issue-0145: Static typing of path expressions in the presence of derivation by extension

Locus: formal-semantics Cluster: Static typing Priority: 1 Status: decided
Originator: Jerome Simeon
Static typing of path expressions in the presence of derivation by extension

Description

The current static type analysis rules for Step expressions is broken in the presence of derivation by extension. This bug is impacting section #FS-sec_steps.

Actual Resolution

Decision by: fs-editors on 2003-01-12 ([link to member only information] )

Dec. FS working draft fixes the static semantics of path expressions in the presence of derivation by extension.

491. FS-Issue-0148: Validation of an empty string against a string list

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: decided
Originator: Jerome Simeon
Validation of an empty string against a string list

Description

The formal semantics assumes that the result of validating an element with empty content or with an empty text node against a list of strings is the empty sequence, not the empty string. Is that consistent with XML Schema?

Proposed Resolution

I think XML Schema is clear that validating and empty element validated against a list type yields an empty element in the PSVI and therefore an empty element in the data model. In the formal semantics that corresponds to validating the content of the element to result in an empty sequence.

I think this issue should be closed and that the current Formal Semantics documents is correct here.

Actual Resolution

Decision by: xquery on 2003-02-12 ([link to member only information] )

JS's proposal ACCEPTED. No changes to the document.

492. FS-Issue-0149: Derivation by extension in XQuery

Locus: formal-semantics Cluster: Language Priority: 1 Status: decided
Originator: Phil Wadler
Derivation by extension in XQuery

Description

If type u is derived from type t by extension, then the formal semantics document specifies that type u may appear wherever type t is expected. It is not clear what the XQuery document says on this point.

Proposed Resolution

The relevant text in the XQuery document can be found in Section 2.4.2.1, "SequenceType Matching", under the description of "ElemOrAttrType", Rules 1 and 2.

Rule 1 describes matching by type-name. It says "The match is successful only if the given element or attribute has a type annotation that is the same as the required type or ... derived from the required type."

Rule 2 describes matching by element-name. It says "The match is successful only if the name of the given element or attribute is equal to the required name or ... derived from the required name, and if the element or attribute has been validated."

Rules 1 and 2 do not distinguish between derivation by extension or by restriction, so by implication they apply to both kinds of derivation. I do not believe that Rules 1 and 2 were intended to apply to derivation by list or union. I believe this should be clarified by changing "derived" to "derived by restriction or extension" in Rules 1 and 2.

I believe that this change will close Issue 492.

Actual Resolution

Decision by: xquery on 2003-01-29 ([link to member only information] )

Decided to accept proposal and thus resolving issue.

493. FS-Issue-0150: May the content of a text node be the empty string?

Locus: formal-semantics Cluster: Language Priority: 1 Status: decided
Originator: Phil Wadler
May the content of a text node be the empty string?

Description

May the content of a text node be the empty string? None of the formal semantics, the datamodel, or the XQuery document addresses this point.

Actual Resolution

Decision by: xquery on 2003-02-26 ([link to member only information] )

Add a constraint that a text node must consist of at least one character information items to the Data Model.

496. FS-Issue-0153: Support for lax and strict wildcards

Locus: formal-semantics Cluster: Semantics Priority: 1 Status: active
Originator: FS Editors
Support for lax and strict wildcards

Description

The Formal Semantics does not currently model lax and strict wildcards. The mapping in Section 7, only describes how XML Schema wilcards with the 'skip validation' semantics are imported into the XQuery Type System.

499. FS-Issue-0156: Casting and validation

Locus: formal-semantics Cluster: Lan