Copyright © 2003 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark, document use and software licensing rules apply.
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.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.
This is a public W3C Working Draft for review by W3C Members and other interested parties. Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document 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 section entitled "Processing
Model" that provides a more complete and detailed description
of expression processing. It also contains specific error codes
for various error conditions, and a glossary in which many
terms are defined. The section on Optional Features has been
rewritten. The term Basic XQuery is no longer used.
A new optional
feature called the Full Axis Feature (supporting all the XPath
axes except namespace
) has been added. Three new
types of computed constructors are introduced, and the syntax
for declaring various objects in module prologs has
changed. Changes have been made in the details of
certain kinds of expressions. A complete list of changes can be
found in I Revision
Log.
Public comments on this document are welcome. Feedback is especially requested on the remaining open XQuery issues: Issues 152, 307, 546, 554, and 564. 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/).
This Working Draft references the Last Call Working Drafts of [XQuery 1.0 and XPath 2.0 Data Model] and [XQuery 1.0 and XPath 2.0 Functions and Operators]. Since these Last Call Working Drafts are not being re-published along with this Working Draft, it is possible that some differences may exist between this Working Draft and the Last Call Working Drafts. The public is encouraged to provide feedback on any differences that they find. The Working Groups are planning to publish a set of synchronized documents as early as possible.
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.
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.
1 Introduction
2 Basics
2.1 Expression
Context
2.1.1 Static Context
2.1.1.1
Predefined Types
2.1.2 Dynamic Context
2.2 Processing Model
2.2.1 Data Model Generation
2.2.2 Schema Import
Processing
2.2.3 Expression Processing
2.2.3.1
Static Analysis Phase
2.2.3.2
Dynamic Evaluation
Phase
2.2.4 Serialization
2.2.5 Consistency Constraints
2.3 Important Concepts
2.3.1 Document Order
2.3.2 Typed Value and String Value
2.3.3 Input Sources
2.4 Types
2.4.1 SequenceType
2.4.1.1
SequenceType
Matching
2.4.2 Type Conversions
2.4.2.1
Atomization
2.4.2.2
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 Schema Import Feature
2.6.2 Static Typing Feature
2.6.3 Full Axis 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 Context Item Expression
3.1.5 Function Calls
3.1.6 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
Namespace Declaration
Attributes
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 Other Direct Constructors
3.7.3 Computed Constructors
3.7.3.1
Computed Element
Constructors
3.7.3.2
Computed Attribute
Constructors
3.7.3.3
Document Node
Constructors
3.7.3.4
Text Node Constructors
3.7.3.5
Computed Processing Instruction
Constructors
3.7.3.6
Computed Comment
Constructors
3.7.3.7
Computed Namespace
Constructors
3.7.4 Namespace Nodes on Constructed
Elements
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 Module Declaration
4.2 Version Declaration
4.3 Base
URI Declaration
4.4 Namespace Declaration
4.5 Default Namespace Declaration
4.6 Schema
Import
4.7 Module
Import
4.8 Variable Declaration
4.9 Validation Declaration
4.10 Xmlspace Declaration
4.11 Default Collation
Declaration
4.12 Function
Declaration
A XQuery Grammar
A.1 EBNF
A.1.1 Grammar Notes
A.2 Lexical structure
A.2.1 White Space 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 Context
Components
C.1 Static Context
Components
C.2 Dynamic Context
Components
C.3 Serialization
Parameters
D References
D.1 Normative References
D.2 Non-normative
References
D.3 Background References
D.4 Informative Material
E Glossary
F Summary of Error Conditions
G Example Applications
(Non-Normative)
G.1 Joins
G.2 Grouping
G.3 Queries on Sequence
G.4 Recursive
Transformations
H XPath 2.0 and XQuery 1.0 Issues
(Non-Normative)
I Revision Log
(Non-Normative)
I.1 22 August
2003
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].
[Definition: XQuery operates on the abstract, logical structure of an XML document, rather than its surface syntax. This logical structure is known as the data model, which is defined in the [XQuery 1.0 and XPath 2.0 Data Model] document.]
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:
The XQuery data model defines the information in an XML document that is available to an XQuery processor. The data model is defined in [XQuery 1.0 and XPath 2.0 Data Model].
The static and dynamic semantics of XQuery are formally defined in [XQuery 1.0 and XPath 2.0 Formal Semantics]. This document is useful for implementors and others who require a rigorous definition of XQuery.
The type system of XQuery is based on [XML Schema].
The default library of functions and operators supported by XQuery is defined in [XQuery 1.0 and XPath 2.0 Functions and Operators].
One requirement in [XML Query 1.0 Requirements] is that an XML query language have both a human-readable syntax and an XML-based syntax. The XML-based syntax for XQuery is described in [XQueryX 1.0].
Editorial note | |
The current edition of [XQueryX 1.0] has not incorporated recent language changes; it will be made consistent with this document in its next edition. |
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:
[96] | 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.
[Definition: Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementor for each particular implementation.]
[Definition: Implementation-dependent indicates an aspect that may differ between implementations, is not specified by this or any W3C specification, and is not required to be specified by the implementor for any particular implementation.]
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. [Definition: XQuery is a functional language which means that expressions can be nested with full generality. (However, unlike a pure functional language, it does not allow variable substitutability if the variable declaration contains construction of new nodes.)] [Definition: 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.[Definition: A
sequence is an ordered collection of zero or more
items.] [Definition: An item is
either an atomic value or a node.] [Definition: 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).] [Definition: A node is an
instance of 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
.
[Definition: 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). [Definition: 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 4.4 Namespace
Declaration) 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.
[Definition: 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 dynamic context.
[Definition: 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. If analysis of an expression relies on some component of the static context that has not been assigned a value, a static error is raised.[err:XP0001]
The individual components of the static context are summarized below. Further rules governing the semantics of these components can be found in C.1 Static Context Components.
[Definition: XPath 1.0
compatibility mode. This component must be
set by all host languages that include XPath 2.0 as a
subset, indicating whether rules for compatibility
with XPath 1.0 are in effect. XQuery sets the value
of this component to
false
. ]
[Definition: 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.] Each in-scope namespace is classified as either an active namespace or a passive namespace. For details of this distinction, see 3.7.4 Namespace Nodes on Constructed Elements.
Some namespaces are predefined; additional namespaces can be defined by Prologs, by namespace declaration attributes, and by computed namespace constructors.
[Definition: Default element/type 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.] The initial default element/type namespace may be provided by the external environmentor by a declaration in the Prolog of a module.
[Definition: 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. The initial default function namespace may be provided by the external environmentor by a declaration in the Prolog of a module.]
[Definition: 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:
[Definition: In-scope type definitions. The in-scope type definitions always include the predefined types listed in 2.1.1.1 Predefined Types. 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.
[Definition: 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). 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.]
[Definition: 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). If the Schema Import Feature is supported, in-scope attribute declarations include all attribute declarations found in imported schemas.]
[Definition: In-scope variables. This is a set of (QName, type) pairs. It defines the set of variables that are available for reference within an expression. The QName is the name of the variable, and the type is the static type of the variable.]
Variable
declarations in the Prolog of a module are added to the in-scope
variables of the module. An expression
that binds a variable (such as a let
,
for
, some
, or
every
expression) extends the in-scope
variables of its subexpressions with the new bound
variable and its type. Within a function
declaration, the in-scope variables are extended
by the names and types of the function
parameters.
[Definition: In-scope functions. This component defines the set of functions that are available to be called from within an expression. Each function is uniquely identified by its expanded QName and its arity (number of parameters). Each function in in-scope functions has a function signature and a function implementation.] [Definition: The function signature specifies the name of the function and the static types of its parameters and its result.] [Definition: The function implementation enables the function to map instances of its parameter types into an instance of its result type. For a user-defined function, the function implementation is an XQuery expression. For an external function, the function implementation is implementation dependent.]
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.
[Definition: 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.
[Definition: Default collation. This collation is used by string comparison functions when no explicit collation is specified.]
[Definition: Validation
mode. The validation mode specifies the mode in
which validation is performed by element constructors
and by validate
expressions. ] Its value is one of
strict
, lax
, or
skip
. The initial validation mode may be
provided by the environment external to a query or by
the validation declaration in the Prolog of a module.
If no validation mode is specified in either of these
ways, the initial validation mode is
lax
.
The validation mode for a subexpression is
inherited from the containing expression. A
validate
expression that specifies a
mode changes the validation mode of its
subexpressions to the specified mode.
[Definition: Validation
context. An expression's validation context
determines the context in which elements constructed
by the expression are validated. ] Its value is
either global
or a context path that
starts with a top-level element name or type name in
the in-scope schema definitions. The
default validation context of a module is
global
.
The validation context for a subexpression is
inherited from the containing expression. An
element constructor extends the validation
context of its subexpressions with the name of the
constructed element, and a validate
expression that specifies a context redefines the
validation context of its subexpressions.
[Definition: XMLSpace
policy. This policy, declared in the Prolog,
controls the processing of whitespace by element
constructors.] Its value may be preserve
or strip
.
[Definition: Base URI. This
is an absolute URI, used when necessary in the
resolution of relative URIs (for example, by the
fn:resolve-uri
function.)]
[Definition:
Statically-known documents. This is a mapping
from strings onto types. The string represents the
absolute URI of a resource that is potentially
accessible using the fn:doc
function.
The type is the type of the document node that would
result from calling the fn:doc
function
with this URI as its argument. ] If the argument to
fn:doc
is anthing other than a string
literal that is present in statically-known
documents, then the static type of
fn:doc
is
document-node()?
.
[Definition:
Statically-known collections. This is a
mapping from strings onto types. The string
represents the absolute URI of a resource that is
potentially accessible using the
fn:collection
function. The type is the
type of the sequence of nodes that would result from
calling the fn:collection
function with
this URI as its argument.] If the argument to
fn:collection
is anthing other than a
string literal that is present in statically-known
collections, then the static type of
fn:collection
is
node()?
.
The in-scope type definitions in the
static context are initialized
with certain predefined types, including all the
built-in types of [XML
Schema]. 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
.
Element and attribute definitions in the
xs
namespace are not implicitly included
in the static context.
In addition, the predefined types of XQuery include
the 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
xdt
.
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
.
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.
xdt:dayTimeDuration
is a subtype of
xs:duration
whose lexical
representation contains only day, hour, minute, and
second components.
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].
[Definition: The dynamic context of an expression is defined as information that is available at the time the expression is evaluated.] If evaluation of an expression relies on some part of the dynamic context that has not been assigned a value, a dynamic error is raised.[err:XP0002]
The individual components of the dynamic context are summarized below. Further rules governing the semantics of these components can be found in C.2 Dynamic Context Components.
The dynamic context consists of all the components of the static context, and the additional components listed below.
[Definition: The first three components of the dynamic 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.
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.
[Definition: The context
item is the item currently being processed in a
path expression. An item is either an atomic value or
a node.][Definition: 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
.
[Definition: The context
position is the position of the context item
within the sequence of items currently being
processed in a path expression. ]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.
[Definition: The context
size is the number of items in the sequence of
items currently being processed in a path
expression.] 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
.
[Definition: 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. The QName is the name of the variable and the value is the dynamic value of the variable.]
[Definition:
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.]
[Definition: 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.]
[Definition: Accessible
documents. This is a mapping of strings onto
document nodes. The string represents the absolute
URI of a resource. The document node is the
representation of that resource as an instance of the
data model, as returned by the fn:doc
function when applied to that URI. ]The set of
accessible documents may be the same as, or a subset
or superset of, the set of statically-known
documents, and it may be empty.
[Definition:
Accessible collections. This is a mapping of
strings onto sequences of nodes. The string
represents the absolute URI of a resource. The
sequence of nodes represents the result of the
fn:collection
function when that URI is
supplied as the argument. ] The set of accessible
collections may be the same as, or a subset or
superset of, the set of statically-known collections,
and it may be empty.
XQuery is defined in terms of the data model and in terms of the expression context.
Figure 1: Processing Model Overview
Figure 1 provides a schematic overview of the processing steps that are discussed in detail below. XQuery distinguishes between the external processing domain, which includes generation of the data model (see 2.2.1 Data Model Generation), schema import processing (see 2.2.2 Schema Import Processing) and serialization (see 2.2.4 Serialization), and the query processing domain, which includes the static analysis and dynamic evaluation phases (see 2.2.3 Expression Processing). Consistency constraints on the query processing domain are defined in 2.2.5 Consistency Constraints.
Editorial note | |
There is an open issue on how much of the external processing domain is considered normative (open issue 561). |
Before an expression can be processed, the input documents to be accessed by the expression must be represented in the data model. Figure 1 depicts the steps by which an XML document may be converted to the data model:
A document may be parsed using an XML parser that generates an XML Information Set (see [XML Infoset]). The parsed document may then 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). If a document has no associated schema, its Information Set is preserved. (See DM1 in Fig. 1.)
The Information Set or PSVI may be transformed into the data model by a process described in [XQuery 1.0 and XPath 2.0 Data Model]. (See DM2 in Fig. 1.)
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 (see DM3 in Fig. 1.) 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.
Each atomic value, element node, and attribute node in
the data
model is annotated with its dynamic type. The dynamic
type specifies a range of values -- for example, an
attribute named version
might have the
dynamic type xs:decimal
, indicating that it
contains a decimal value. For example, 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 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 xdt:untypedAny
.
An atomic value of unknown type is annotated with the
type xdt:untypedAtomic
.
The in-scope schema definitions in the static context may be extracted from actual XML Schemata as described in [XQuery 1.0 and XPath 2.0 Formal Semantics] (see step SI1 in Figure 1) or may be generated by some other mechanism (see step SI2 in Figure 1). In either case, the result must satisfy the consistency constraints defined in 2.2.5 Consistency Constraints.
XQuery defines two phases of processing called the static analysis phase and the dynamic evaluation phase (see Fig. 1).
[Definition: The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on any input data.]
During the static analysis phase, the query is parsed into an internal representation called the operation tree (step SQ1 in Figure 1). A parse error is raised as a static error.[err:XP0003] The static context is initialized by the implementation (step SQ2). The static context is then changed and augmented based on information in the prolog (step SQ3). In particular, the in-scope schema definitions are populated with information from imported schemata. The static context is used to resolve type names, function names, namespace prefixes and variable names. If a name in the operation tree is not found in the static context, a static error [err:XP0008] is raised (step SQ4).
The operation tree is then normalized by making explicit the implicit operations such as atomization, type promotion and extraction of Effective Boolean Values (step SQ5). The normalization process is described in [XQuery 1.0 and XPath 2.0 Formal Semantics]. An implementation is free to use any strategy or algorithm whose result conforms to these specifications.
If the Static Typing Feature
is supported, each expression is assigned a static type
(step SQ6). [Definition: 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 and XPath 2.0
Formal Semantics].] 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
.
During the analysis phase, if the Static Typing Feature 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.[err:XQ0004] 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.
During the static analysis phase, if the
static
type assigned to an expression other than
()
is empty, a static error is
raised.[err:XQ0005] This catches cases in
which a query refers to an element or attribute that is
not present in the in-scope
schema definitions, possibly because of a spelling
error.
The purpose of type-checking during the static analysis phase is to provide early detection of type errors and to infer type information that may be useful in optimizing the evaluation of an expression.
[Definition: The dynamic evaluation phase is performed only after successful completion of the static analysis phase. The dynamic evaluation phase depends on the operation tree of the expression being evaluated (step DQ1), on the input data (step DQ4), and on the dynamic context (step DQ5), which in turn draws information from the external environment (step DQ3) and the static context (step DQ2).] Execution of the evaluation phase may create new data-model values (step DQ4) and it may extend the dynamic context (step DQ5)--for example, by binding values to variables.
Editorial note | |
This is an open issue. It would be possible to evaluate an expression containing a static type error, and this might be quite useful because static analysis is conservative. Static type analysis could be used to warn of potential errors without inhibiting execution of an expression. |
[Definition: 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 evaluation time its value may have the dynamic type "integer.")]
If an operand of an expression is found to have a dynamic type that is not appropriate for that operand, a type error is raised.[err:XP0006]
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
xdt:untypedAtomic
. 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.
[Definition: Serialization is the process of converting an instance of the [XQuery 1.0 and XPath 2.0 Data Model] into a sequence of octets (step DM4 in Figure 1.) ] 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
serialization parameters listed (with default values)
in C.3
Serialization Parameters.
In order for an expression to be well defined, the expression, its static context, and its dynamic context must be mutually consistent. The consistency constraints listed below are prerequisites for correct functioning of an XQuery implementation. Enforcement of these consistency constraints is beyond the scope of this specification.
For each item type (i.e., element, attribute, or type name) referenced in an instance of the data model whose expanded name matches a name in the in-scope schema definitions (ISSD), the corresponding element, attribute, or type definition in the ISSD must be equivalent to the definition originally provided in the PSVI from which the data model instance was created.
Every item type (i.e., every element, attribute, or type name) referenced in in-scope variables or in-scope functions must be in the in-scope schema definitions.
Every name used in a SequenceType must be in the in-scope schema definitions.
The element declaration for every element name referenced in a SequenceType or KindTest must be in the in-scope element declarations.
The attribute declaration for every attribute name referenced in a SequenceType or KindTest must be in the in-scope attribute declarations.
For each mapping of a string to a document node in accessible documents, if there exists a mapping of the same string to a document type in statically-known documents, the document node must match the document type, using the matching rules in 2.4.1.1 SequenceType Matching.
For each mapping of a string to a sequence of nodes in accessible collections, if there exists a mapping of the same string to a type in statically-known collections, the sequence of nodes must match the type, using the matching rules in 2.4.1.1 SequenceType Matching.
The dynamic variables in the dynamic context and the in-scope variables in the static context must correspond as follows:
All variables defined in in-scope variables must be defined in dynamic variables.
For each (variable, type) pair in in-scope variables and the corresponding (variable, value) pair in dynamic variables such that the variable names are equal, the value must match the type, using the matching rules in 2.4.1.1 SequenceType Matching.
The concepts described in this section are normatively defined in [XQuery 1.0 and XPath 2.0 Data Model] and [XQuery 1.0 and XPath 2.0 Functions and Operators]. They are summarized here because they are of particular importance in the processing of expressions.
[Definition: Document order defines a total ordering among all the nodes seen by the language processor and is defined formally in the data model.] 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 dependent 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 dependent but stable.
Nodes have a typed value and a string value.
[Definition: The typed value
of a node is a sequence of atomic values and can be
extracted by applying the fn:data
function
to the node. The typed value for each kind of node is
defined by the dm:typed-value
accessor in
[XQuery 1.0 and XPath 2.0 Data
Model]. ] [Definition:
The string value of a node is a string and can be
extracted by applying the the fn:string
function to the node. The string value for each kind of
node is defined by the dm:string-value
accessor in [XQuery 1.0 and XPath
2.0 Data Model].] [Definition: Element and
attribute nodes have a type annotation, which
represents (in an implementation-dependent way) 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 relationship between the typed value and the string value for various kinds of nodes is described and illustrated by examples below.
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.)
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
).
For an element node, the relationship between typed value and string value depends on the node's type annotation, as follows:
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
.
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
.
If the type annotation denotes a complex type with empty content, then the typed value of the node is the empty sequence.
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 a type error
[err:XP0007] 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.
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].
An expression can access input documents either by calling one of the input functions or by referencing some part of the expression context that is initialized by the external environment, such as a variable or a pre-initialized context item.
The input functions supported by XQuery are as follows:
The fn:doc
function takes a string
containing a URI that refers to an XML document, and
returns a document node whose content is the
data
model representation of the given document.
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
.
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.
XQuery is a strongly typed language with a type system based on [XML Schema]. The XQuery type system is formally defined in [XQuery 1.0 and XPath 2.0 Formal Semantics]. During the analysis phase, if static type checking is in effect and an expression has a static type that is not appropriate for the context in which the expression is used, a type error is raised.[err:XQ0004] During the evaluation phase, if the type of a value is incompatible with the expected type of the context in which the value is used, a type error is raised.[err:XP0006] A type error may be detected and reported either during the static analysis phase or during the dynamic evaluation phase.
[Definition: 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.]
[124] | SequenceType |
::= | (ItemType
OccurrenceIndicator?) |
[140] | OccurrenceIndicator |
::= | "?" | "*" | "+" |
[126] | ItemType |
::= | AtomicType
| KindTest | ("item"
"(" ")") |
[125] | AtomicType |
::= | QName |
[127] | KindTest |
::= | DocumentTest |
[130] | PITest |
::= | "processing-instruction" "(" (NCName | StringLiteral)?
")" |
[132] | CommentTest |
::= | "comment" "(" ")" |
[133] | TextTest |
::= | "text" "(" ")" |
[134] | AnyKindTest |
::= | "node" "(" ")" |
[131] | DocumentTest |
::= | "document-node" "(" ElementTest? ")" |
[128] | ElementTest |
::= | "element" "(" ((SchemaContextPath
LocalName) |
[129] | AttributeTest |
::= | "attribute" "(" ((SchemaContextPath "@"
LocalName) |
[135] | SchemaContextPath |
::= | SchemaGlobalContext
"/" (SchemaContextStep
"/")* |
[14] | SchemaGlobalContext |
::= | QName |
SchemaGlobalTypeName |
[15] | SchemaContextStep |
::= | QName |
[13] | SchemaGlobalTypeName |
::= | "type" "(" QName ")" |
[137] | LocalName |
::= | QName |
[138] | NodeName |
::= | QName |
"*" |
[139] | 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/type namespace. It is a static error [err:XP0008] 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
[Definition: During
evaluation 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.
Editorial note | |
The definition of SequenceType matching still needs to be correlated with the definition of type matching in [XQuery 1.0 and XPath 2.0 Formal Semantics]. |
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
The ItemType item()
matches any
single item. For example, item()
matches the atomic value 1
or the
element <a/>
.
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, but can often be
replaced by an atomic type with an occurrence
indicator, such as xs:IDREF*
.)
The following ItemTypes (referred to generically as KindTests) match nodes:
node()
matches any node.
text()
matches any text
node.
processing-instruction()
matches any processing instruction node.
processing-instruction(
N
)
matches any processing instruction
node whose name (called its "PITarget" in XML)
is equal to N, where N is an
NCName. Example:
processing-instruction(xml-stylesheet)
matches any processing instruction whose
PITarget is xml-stylesheet
.
For backward compatibility with XPath 1.0,
the PITarget of a processing instruction in a
KindTest may also be expressed as a string
literal, as in this example:
processing-instruction("xml-stylesheet")
.
comment()
matches any comment
node.
document-node()
matches any
document node.
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),
mixed with zero or more comments and processing
instructions. Example:
document-node(element(book))
matches any document node whose content
contains exactly one element node named
book
, that conforms to the schema
declaration for the top-level element
book
(possibly mixed with comments
and processing instructions).
An ElementTest (see below) matches an element node, optionally qualifying the node by its name, its type, or both.
An AttributeTest (see below) matches an attribute node, optionally qualifying the node by its name, its type, or both.
[Definition: An ElementTest is used to match an element node by its name and/or type.] An ElementTest may take one of the following forms:
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.
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:
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:
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 the
nilled
property 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)
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:
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:
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)
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, *)
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)
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:
the name of the given element node is equal to the last name in the path (expanded QNames match), and:
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)
[Definition: An AttributeTest is used to match an attribute node by its name and/or type.] An AttributeTest may take one of the following forms:
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.
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:
the name of the given attribute node is equal to N (expanded QNames match), and:
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)
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:
the name of the given attribute node is equal to N (expanded QNames match), and:
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)
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, *)
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)
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:
the name of the given attribute node is equal to the last name in the path (expanded QNames match), and:
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)
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 3.1.5 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.
Type conversions sometimes depend on a process
called atomization. [Definition: Atomization is
applied to a value when the value is used in a context
in which 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
Under certain circumstances (listed below), it is
necessary to find the effective
boolean value of a value. [Definition: The effective boolean
value of a value is defined as the result of
applying the fn:boolean
function to the
value, 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
.
As described in 2.2.3 Expression Processing, XQuery defines an analysis phase, which does not depend on input data, and an evaluation phase, which does depend on input data. Errors may be raised during each phase.
[Definition: A static error is an error that must be detected during the analysis phase. A syntax error is an example of a static error. The means by which static errors are reported during the analysis phase is implementation defined. ]
[Definition: A dynamic error is an error that must be detected during the evaluation phase and may be detected during the analysis phase. Numeric overflow is an example of a dynamic error. ]
[Definition: A type error may be raised during the analysis or evaluation phase. During the analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs. ]
The result of the analysis phase is either success or one or more type errors and/or static errors.
The result of the evaluation phase is either a result value, a type error, or a dynamic error. 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 and XPath 2.0 Formal Semantics].
If any expression (at any level) can be evaluated
during the analysis phase (because all its explicit
operands are known and it has no dependencies on the
dynamic context), then any error in performing this
evaluation may be reported as a static error. However,
the fn:error()
function must not be
evaluated during the analysis phase. For example, an
implementation is allowed (but not required) to treat the
following expression as a static error, because it calls
a constructor function with a constant string that is not
in the lexical space of the target type:
xs:date("Next Tuesday")
[XQuery 1.0 and XPath 2.0 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.
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 the sub-expressions ($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. [Definition: An error value is a single item or the 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
div
operator raises an error if its second
operand equals zero.
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 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)))
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 and XPath 2.0 Formal Semantics]. In such cases, dynamic errors may be raised that would not have been raised 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 raise a casting error if it is evaluated exactly as written (i.e., left to right). 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 raise an error. However, an expression must not be rearranged in a way that causes it to return a result value that is different from the result value defined by [XQuery 1.0 and XPath 2.0 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 expressions that provide guaranteed conditions under
which a particular subexpression will not be
evaluated.
XQuery defines three optional features called the Schema Import Feature, the Static Typing Feature, and the Full Axis Feature.
If an XQuery implementation that does not support the Schema Import Feature encounters a Schema Import, it raises a static error.[err:XQ0009] In such an implementation, the in-scope type definitions consist only a fixed set of predefined types.
Editorial note | |
This set is to be determined. |
If the Schema Import Feature is supported, 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 is raised.[err:XQ0012]
[Definition: An XQuery implementation that does not support the Static Typing Feature is not required to raise type errors during the static analysis phase.] However, non-type-related static errors must be detected and raised during the static analysis phase.
An XQuery implementation that does not support the Full Axis Feature raises a static error [err:XQ0010] if any of the following axes are encountered in a path expression:
ancestor ancestor-or-self following following-sibling preceding preceding-sibling
An XQuery implementation that supports the Full Axis
Feature must recognize the axes on the above list
(however, XQuery does not recognize the
namespace
axis defined by XPath).
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.
[Definition: A pragma may be used to provide additional information to an XQuery implementation.]
[1] | Pragma |
::= | "(::" "pragma" QName PragmaContents*
"::)" |
/* gn: 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. See
A.2 Lexical
structure for the exact lexical states where
pragmas are recognized. A pragma is identified by its
QName.
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.[err:XQ0013] 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($doc//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.
[Definition: An implementation may extend XQuery functionality by supporting must-understand extensions. A must-understand extension may be used anywhere that ignorable whitespace is allowed.]
[2] | MUExtension |
::= | "(::" "extension" QName ExtensionContents*
"::)" |
/* gn: 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 "::)
". See A.2 Lexical structure
for the exact lexical states where these extensions
are recognized. A must-understand extension is
identified by its QName.
If an implementation does not support a must-understand extension, then a static error is raised.[err:XQ0014] 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.
[Definition: 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. If the XQuery Flagger is enabled, a static error [err:XQ0015] is raised if the query 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.
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].
[40] | Expr |
::= | ExprSingle (","
ExprSingle)* |
[41] | ExprSingle |
::= | FLWORExpr |
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.
[Definition: 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.
[75] | PrimaryExpr |
::= | Literal |
FunctionCall |
ContextItemExpr |
("$" VarName) | ParenthesizedExpr |
Constructor |
[20] | VarName |
::= | QName |
[Definition: A literal is a direct syntactic representation of an atomic value.] XQuery supports two kinds of literals: numeric literals and string literals.
[93] | Literal |
::= | NumericLiteral | StringLiteral |
|
[94] | 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 */ |
[16] | Digits |
::= | [0-9]+ |
|
[23] | HexDigits |
::= | [0-9] | [a-f] | [A-F]+ |
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.
Note:
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 |
< |
< |
> |
> |
& |
& |
" |
" |
' |
' |
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 €
.
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 & Jerry's
denotes the string "Ben &
Jerry's
".
€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
.
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:
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.
A variable may be added to the in-scope variables by the host language environment.
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 [err:XP0016] 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.
[95] | 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.
[74] | ContextItemExpr |
::= | "." |
A context item expression evaluates to the
context item, which may be either a node (as in the
expression
fn:doc("bib.xml")//book[count(./author)>1]
)
or an atomic value (as in the expression (1 to
100)[. mod 5 eq 0]
).
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.[err:XP0017]
[96] | FunctionCall |
::= | QName "("
(ExprSingle (","
ExprSingle)*)?
")" |
A function call is evaluated as follows:
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.
Each argument value is converted by applying the function conversion rules listed below.
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.
If the function is a user-declared 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. It is a static error [err:XP0018] for an expression to depend on the focus when the focus is undefined.
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:
Atomization is applied to the given value, resulting in a sequence of atomic values.
Each item in the atomic sequence that is of
type xdt:untypedAtomic
is cast to
the expected atomic type.
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.[err:XP0006] 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 4.4 Namespace Declaration.
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] | ExprComment |
::= | "(:" (ExprCommentContent |
ExprComment)*
":)" |
/* gn: comments */ |
[4] | ExprCommentContent |
::= | Char |
/* gn: parens */ |
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. 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 :)
A path expression can be used to locate nodes within a tree.
[69] | PathExpr |
::= | ("/" RelativePathExpr?) |
/* gn: leading-lone-slash */ |
[70] | 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 type error is raised.[err:XP0019] 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 Dynamic Context. Each
evaluation of E2
must result in a sequence of
nodes; otherwise, a type error is raised.[err:XP0019] 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()) treat as
document-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.[err:XP0020] At evaluation time, if the
root node above the context node is not a document node, a
dynamic
error is raised.[err:XP0050]
A "//
" at the beginning of a path
expression is an abbreviation for the initial steps
fn:root(self::node()) treat as
document-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 type error is raised.[err:XP0020] At
evaluation time, if the root node above the context node is
not a document node, a dynamic error is raised.[err:XP0050]
[71] | StepExpr |
::= | AxisStep |
FilterStep |
[72] | AxisStep |
::= | (ForwardStep | ReverseStep) Predicates |
[73] | FilterStep |
::= | PrimaryExpr Predicates |
[84] | ForwardStep |
::= | (ForwardAxis NodeTest) | AbbrevForwardStep |
[85] | ReverseStep |
::= | (ReverseAxis NodeTest) | AbbrevReverseStep |
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. If the context item is not a node, a type error is raised.[err:XP0020]
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.
[88] | ForwardAxis |
::= | ("child" "::") |
[89] | ReverseAxis |
::= | "parent" "::" |
XQuery supports the following axes (subject to limitations as described in 2.6.3 Full Axis Feature):
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 ancestor
axis contains the
ancestors of the context node; the ancestors of the
context node consist of the parent of context node
and the parent's parent and so on; thus, the
ancestor axis will always include the root node,
unless the context node is the root node
the following-sibling
axis contains
all the following siblings of the context node; if
the context node is an attribute node or namespace
node, the following-sibling
axis is
empty
the preceding-sibling
axis contains
all the preceding siblings of the context node; if
the context node is an attribute node or namespace
node, the preceding-sibling
axis is
empty
the following
axis contains all
nodes, in the same tree as the context node, that
are after the context node in document order,
excluding any descendants and excluding attribute
nodes and namespace nodes
the preceding
axis contains all
nodes, in the same tree as the context node, that
are before the context node in document order,
excluding any ancestors and excluding attribute
nodes and namespace nodes
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
the ancestor-or-self
axis contains
the context node and the ancestors of the context
node; thus, the ancestor-or-self axis will always
include the root 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.
The parent
, ancestor
,
ancestor-or-self
, preceding
,
and preceding-sibling
axes are reverse
axes; all other axes are forward axes. The
ancestor
, descendant
,
following
, preceding
and
self
axes partition a document (ignoring
attribute and namespace nodes): they do not overlap and
together they contain all the nodes in the
document.
In a sequence of nodes selected by a step, the context positions of the nodes are determined in a way that depends on the axis. If the axis is a forward axis, context positions are assigned to the nodes in document order. If the axis is a reverse axis, context positions are assigned to the nodes in reverse document order. In either case, the first context position is 1.
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.
[90] | NodeTest |
::= | KindTest |
NameTest |
|
[91] | NameTest |
::= | QName |
Wildcard |
|
[92] | Wildcard |
::= | "*" |
/* 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 [err:XP0008] 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/type 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.[err:XP0008] 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 2.4.1 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)
, mixed with zero or more
comments and processing instructions.
[76] | 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
Dynamic 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:
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.
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]
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
ancestor::div
selects all
div
ancestors of the context node
ancestor-or-self::div
selects the
div
ancestors of the context node and,
if the context node is a div
element,
the context node as well
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
following-sibling::chapter[fn:position() =
1]
selects the next chapter
sibling of the context node
preceding-sibling::chapter[fn:position() =
1]
selects the previous chapter
sibling 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
[86] | AbbrevForwardStep |
::= | "@"? NodeTest |
[87] | AbbrevReverseStep |
::= | ".." |
The abbreviated syntax permits the following abbreviations:
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, the path expression
section/para
is an abbreviation for
child::section/child::para
, and the path
expression section/@id
is an
abbreviation for
child::section/attribute::id
. Similarly,
section/attribute(@id)
is an
abbreviation for
child::section/attribute::attribute(@id)
.
Note that the latter expression contains both an axis
specification and a node test.
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
.
//
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.
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.
Note:
The expression .
, known as a context
item expression, is a primary expression,
and is described in 3.1.4 Context Item
Expression.
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
.//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 type
attribute 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.
XQuery supports operators to construct and combine sequences of items. Sequences are never nested--for example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3).
[40] | Expr |
::= | ExprSingle
("," ExprSingle)* |
[62] | 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
. A type error [err:XP0006] is raised 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
.
[66] | UnionExpr |
::= | IntersectExceptExpr
( ("union" | "|") IntersectExceptExpr
)* |
[67] | IntersectExceptExpr |
::= | ValueExpr (
("intersect" | "except") ValueExpr )* |
[68] | 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.[err:XP0006]
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.
XQuery provides arithmetic operators for addition, subtraction, multiplication, division, and modulus, in their usual binary and unary forms.
[63] | AdditiveExpr |
::= | MultiplicativeExpr (
("+" | "-") MultiplicativeExpr
)* |
[64] | MultiplicativeExpr |
::= | UnaryExpr (
("*" | "div" | "idiv" | "mod") UnaryExpr )* |
[65] | 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:
Atomization is applied to each operand.
If either operand is now an empty sequence, the result of the operation is an empty sequence.
If either operand is now a sequence of length greater than one, a type error is raised.[err:XP0006]
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 dynamic error is
raised.[err:XP0021]
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.
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)
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.
[61] | ComparisonExpr |
::= | RangeExpr (
(ValueComp |
|
[81] | ValueComp |
::= | "eq" | "ne" | "lt" | "le" | "gt" |
"ge" |
|
[80] | GeneralComp |
::= | "=" | "!=" | "<" | "<=" | ">" |
">=" |
/* gn: lt */ |
[82] | NodeComp |
::= | "is" | "isnot" |
|
[83] | OrderComp |
::= | "<<" | ">>" |
Value comparisons are intended for comparing single values. The result of a value comparison is defined by applying the following rules, in order:
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.[err:XQ0004][err:XP0006]
Any atomized operand that has the dynamic type
xdt:untypedAtomic
is cast to the type
xs:string
.
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.[err:XQ0004][err:XP0006]
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)
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:
If either atomic value has the dynamic type
xdt:untypedAtomic
, that value is cast to
a required type, which is determined as follows:
If the dynamic type of the other atomic value
is a numeric type, the required type is
xs:double
.
If the dynamic type of the other atomic value
is xdt:untypedAtomic
, the required
type is xs:string
.
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.[err:XP0021]
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.
The result of a node comparison is defined by applying the following rules, in order:
Each operand must be either a single node or an empty sequence; otherwise a type error is raised.[err:XQ0004][err:XP0006]
If either operand is an empty sequence, the result of the comparison is an empty sequence.
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>
The result of an order comparison is defined by applying the following rules, in order:
Both operands must be either a single node or an empty sequence; otherwise a type error is raised.[err:XQ0004][err:XP0006]
If either operand is an empty sequence, the result of the comparison is an empty sequence.
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
.
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"]
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
.
[55] | OrExpr |
::= | AndExpr ( "or"
AndExpr )* |
[56] | 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 2.4.2.2 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 the same dynamic error.
The not
function is described in [XQuery 1.0 and XPath 2.0
Functions and Operators].
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]). Two kinds of constructors are provided: direct constructors, which use an XML-like notation, and computed constructors, which use a notation based on enclosed expressions.
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.
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 a static error.[err:XP0003]
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 if they are copies of existing nodes.
The Base URI of a constructed element node is taken from the static context. The Base URIs of the copied descendant nodes are also taken from the static context rather than by preserving their original Base URIs.
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 Namespace Declaration Attributes) 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:
Predefined entity references and character references in the attribute content are expanded into their referenced strings, as described in 3.1.1 Literals.
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.)
Each enclosed expression is converted to a string as follows:
Atomization is applied to the value of the enclosed expression, converting it to a sequence of atomic values.
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.
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.
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
.
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, by namespace declaration attributes, or by computed namespace constructors. It is a static error to use a namespace prefix that has not been bound to a namespace.[err:XP0008]
A namespace declaration attribute is used
inside a direct element constructor, and serves to
add a namespace to the in-scope namespaces for
the constructed element. 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.[err:XQ0022] A namespace declaration
attribute does not cause an attribute node to be
created. Namespace declaration attributes are
discussed further in 4.4 Namespace
Declaration 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>
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:
The content is evaluated to produce a sequence of nodes called the content sequence, as follows:
Predefined entity references and character references are expanded into their referenced strings, as described in 3.1.1 Literals.
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.
Each nested element constructor is evaluated according to the rules in this section, resulting in a new element node.
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.
If the content sequence contains a document node, a type error is raised.[err:XQ0023]
If the content sequence contains an attribute node following a node that is not an attribute node, a type error is raised.[err:XQ0024] 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, a dynamic error is raised.[err:XQ0025]
Adjacent text nodes in the content sequence are coalesced into a single text node by concatenating their contents, with no intervening blanks.
The resulting sequence of nodes becomes the children and attributes of the new element node in the data model representation.
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
".
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
 
are not considered to be
boundary whitespace, and are always preserved.
Example:
<a> {"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
.
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 a
dynamic error [err:XQ0026] 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.[err:XQ0027]
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>
XQuery allows a query to generate a processing instruction, an XML comment, or a CDATA section directly in the query result. In each case, this is accomplished by using a constructor expression whose syntax is based on the syntax of the equivalent construct in XML.
[105] | CdataSection |
::= | "<![CDATA[" Char* "]]>" |
/* ws: significant */ |
[106] | XmlPI |
::= | "<?" PITarget Char* "?>" |
/* ws: explicit */ |
[18] | PITarget |
::= | NCName |
|
[107] | 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 processing instruction may not
contain the string "?>
", the content of
an XML comment may not contain the string
"-->
", and the content of a CDATA
section may not contain the string
"]]>
" .
The following example illustrates a constructed processing instruction:
<?format role="output" ?>
The following example illustrates a constructed XML comment:
<!-- Tags are ignored in the following section -->
Note that an XML comment constructor actually constructs a comment node in the data model. An XQuery comment, on the other hand, (see 3.1.6 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 -->
The following example illustrates a constructed CDATA 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.
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
,
text
, pi
(denoting a
processing instruction), comment
, or
namespace
.
For those kinds of nodes that have names (element, attribute, processing instruction, and namespace nodes), the keyword that specifies the node kind is followed by the name of the node to be created. This name may be specified either as a QName or (except for namespace nodes) as an expression enclosed in braces, called the name expression, that returns a string or 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.
[99] | CompElemConstructor |
::= | (("element" QName "{") | ("element" "{"
Expr "}" "{")) Expr? "}" |
[101] | CompAttrConstructor |
::= | (("attribute" QName "{") | ("attribute" "{"
Expr "}" "{")) Expr? "}" |
[98] | CompDocConstructor |
::= | "document" "{" Expr "}" |
[104] | CompTextConstructor |
::= | "text" "{" Expr? "}" |
[102] | CompXmlPI |
::= | (("pi" NCName "{") | ("pi" "{"
Expr "}" "{")) Expr? "}" |
[103] | ComputedXmlComment |
::= | "comment" "{" Expr "}" |
[100] | CompNSConstructor |
::= | ("namespace" NCName "{") 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" } } }
The name expression of a computed element constructor is processed as follows:
If the name expression returns an expanded QName, that QName is used as the name of the constructed element.
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. A dynamic error is raised if the string cannot be cast to a QName [err:XP0021] or if expansion of its prefix is not successful.[err:XP0008]
If the name expression does not return a QName or a string, a type error is raised.[err:XQ0004][err:XP0006]
The content expression of a computed element constructor is processed as follows:
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. Any sequence of adjacent
text nodes in the content sequence is merged into
a single text node.
If the content sequence contains a document node, a type error is raised.[err:XQ0023]
If the content sequence contains a namespace node following a node that is not a namespace node, a type error is raised.[err:XQ0040] Namespace nodes occurring in the content sequence are attached to the constructed element node.
If the content sequence contains an attribute node following a node that is not an attribute node or a namespace node, a type error is raised.[err:XQ0024] Attribute nodes occurring in 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.[err:XQ0025]
Element, text, comment, and processing instruction nodes in the content sequence become the children of the constructed element node.
The Base URI of a constructed element node is taken from the static context. The Base URIs of the copied descendant nodes are also taken from the static context rather than by preserving their original Base URIs.
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
$e
(including its attributes, if any)
has been preserved. The first enclosed expression
after the element
keyword generates the
name of the element, and the second enclosed
expression generates the content and attributes:
element {data($dict/entry[word=name($e)]/variant[lang="Italian"])} {$e/@*, $e/*}
The result of this expression is as follows:
<indirizzo>123 Roosevelt Ave. Flushing, NY 11368</indirizzo>
Additional examples of computed element constructors can be found in G.4 Recursive Transformations.
The name expression of a computed attribute constructor is processed as follows:
If the name expression returns an expanded QName, that QName is used as the name of the constructed attribute.
If the name expression returns a string, that
string is cast to a QName and the resulting
expanded QName is used as the name of the
constructed attribute. However, if the string
begins with xmlns
, a dynamic
error is raised.[err:XQ0044] If the string cannot
be cast to a QName, a dynamic error is
raised.[err:XP0021]
If the name expression does not return a QName or a string, a dynamic error is raised.[err:XP0006]
The content expression of a computed attribute constructor is processed as follows:
Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.
If the result of atomization is an empty sequence, the value of the attribute is the zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string.
The individual strings resulting from the
previous step are merged into a single string by
concatenating them with a single space character
between each pair. The resulting string, as an
instance of xs:untypedAtomic
, is the
value of the attribute.
A computed attribute constructor does not perform any automatic validation of the constructed attribute. However, if the computed attribute constructor is inside an element constructor, the attribute will be validated during validation of its parent element.
Example:
attribute size {4 + 3}
The value of the size
attribute
is "7
".
Example:
attribute { if ($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
.
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:
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.
If the content sequence contains a document, attribute, or namespace node, a type error is raised.[err:XQ0028]
The resulting sequence of nodes becomes the children of the new document node.
The base URI of a constructed document node is taken from the static context.
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.
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:
Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.
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.
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.
The following example illustrates a text node constructor:
text {"Hello"}
A computed processing instruction constructor (CompXmlPI) constructs a new processing instruction node with its own node identity. The name expression of a computed processing instruction constructor is processed as follows:
If the name expression returns an expanded QName: If the URI part of the QName is empty, the local part of the QName is used as the name (target) of the processing instruction; otherwise a dynamic error is raised.[err:XQ0041]
If the name expression returns a string, that string is cast to a QName, which is then treated as in the previous item. If the cast fails, a dynamic error is raised.[err:XP0021]
If the name expression does not return a QName or a string, a dynamic error is raised.[err:XP0006]
The content expression of a computed processing instruction constructor is processed as follows:
Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.
If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string.
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 processing instruction.
The following query contains an example of a computed processing instruction constructor. The result of the query is a processing instruction node.
let $target := "audio-output", $content := "beep" return pi {$target} {$content}
A computed comment constructor (ComputedXMLComment) constructs a new comment node with its own node identity. The content expression of a computed comment constructor is processed as follows:
Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.
If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string.
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 comment.
The following query contains an example of a computed comment constructor. The result of the query is a comment node.
let $homebase := "Houston" return comment {fn:concat($homebase, ", we have a problem.")}
A computed namespace constructor (CompNSConstructor) constructs a new namespace node with its own node identity. The immediately enclosing expression of the computed namespace constructor must be a computed element constructor; otherwise a static error is raised.[err:XQ0042] The constructed namespace node is attached to the element node constructed by the enclosing expression.
A constructed namespace node is the dynamic equivalent of a namespace declaration attribute. It binds a namespace prefix to a URI and adds the namespace prefix to the in-scope namespaces for its enclosing element.
The name expression of a computed namespace constructor is processed as follows:
If the name expression returns an expanded QName: If the URI part of the QName is empty, the local part of the QName is used as the name (prefix) of the namespace node; otherwise a dynamic error is raised.[err:XQ0041] If two or more computed namespace constructors within the same computed element constructor attempt to bind the same prefix, a dynamic error is raised.[err:XQ0043]
If the name expression returns a string, that string is cast to a QName, which is then treated as in the previous item. If the cast fails, a dynamic error is raised.[err:XP0021]
If the name expression does not return a QName or a string, a dynamic error is raised.[err:XP0006]
The content expression of a computed namespace constructor is processed as follows:
Atomization is applied to the value of the content expression, converting it to a sequence of atomic values.
If the result of atomization is an empty sequence, it is replaced by a zero-length string. Otherwise, each atomic value in the atomized sequence is cast into a string.
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 (URI) of the constructed namespace node.
The following query contains an example of a
computed namespace constructor, properly nested
within a computed element constructor. The computed
namespace constructor defines the namespace prefix
metric
, which is used in a computed
attribute constructor.
let $ename := "altitude", $evalue := "10000", $nsURI := "http://example.org/metric-system", $attrname := "metric:unit", $attrvalue := "meter" return element {$ename} { namespace metric {$nsURI}, attribute {$attrname} {$attrvalue}, $evalue }
The previous example is equivalent to the following direct element constructor:
<altitude xmlns:metric = "http://example.org/metric-system" metric:unit = "meter">10000</altitude>
When an element node is constructed by either a
direct or computed element constructor, it may have
some attached namespace nodes. These namespace nodes do
not affect the resolution of namespace prefixes during
query processing. The resolution of namespace prefixes
during processing of a query expression is done
strictly according to the in-scope
namespaces of the expression. The namespace nodes
that are attached to an element may affect the way the
element is serialized (see 2.2.4 Serialization).
Namespace nodes may also affect the behavior of certain
functions that operate on nodes, such as
fn:name
.
This section specifies the namespace nodes that are
attached to a constructed element. For this purpose, it
introduces the terms active namespace and
passive namespace. [Definition: A namespace that
is declared by a namespace declaration attribute in a
direct element constructor, or by a computed namespace
constructor inside a computed element constructor, is
classified as an active namespace.] [Definition: A namespace that
is declared in the Prolog, or that is predefined in the
static context, is classified as a passive
namespace, except for the predefined
xml
namespace, which is classified as
active.]
When an element is constructed by a direct or computed element constructor, the namespace nodes attached to the element node are listed below. These namespace nodes are attached to the element node before any validation takes place.
A namespace node is created corresponding to
each in-scope active namespace--that
is, each namespace declared in a namespace
declaration attribute of this (or any
enclosing) direct element constructor, each
computed namespace within this (or any enclosing)
computed element constructor, and the
xml
namespace. These namespace nodes
use the same prefixes and URIs as the namespace
declarations from which they are derived (the
prefix becomes the name of the namespace node, and
the URI becomes the string value of the namespace
node).
A namespace node is created corresponding to any namespace used in the name of the element or in the names of its attributes. However, a namespace node need not be created if there is already a namespace node for a given namespace URI on a given element. The string value of the created namespace node is the namespace URI of the element or attribute name. The name of the namespace node (which represents the namespace prefix) is implementation-dependent; it must not conflict with the name of any other namespace node for the same element.
Note:
Implementations may in many cases be able to choose a namespace prefix that is familiar to the user, such as a prefix that is associated with the corresponding namespace URI in either the source document or the query. In some cases, for example to avoid duplicate declarations of the same prefix, an arbitrary choice must be made.
Where a namespace node is created to declare the namespace URI used in an element name, the namespace prefix can be null (that is, the default namespace can be used) provided this does not clash with an existing declaration of the default namespace on the same element. A namespace node created to declare the namespace URI of an attribute name cannot use a null prefix, because attributes never use the default namespace URI.
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
.
[42] | FLWORExpr |
::= | (ForClause |
LetClause)+ WhereClause? OrderByClause? "return"
ExprSingle |
[43] | ForClause |
::= | "for" "$" VarName TypeDeclaration?
PositionalVar?
"in" ExprSingle (","
"$" VarName TypeDeclaration?
PositionalVar?
"in" ExprSingle)* |
[45] | LetClause |
::= | "let" "$" VarName TypeDeclaration? ":="
ExprSingle ("," "$"
VarName TypeDeclaration? ":="
ExprSingle)* |
[122] | TypeDeclaration |
::= | "as" SequenceType |
[44] | PositionalVar |
::= | "at" "$" VarName |
[46] | WhereClause |
::= | "where" Expr |
[47] | OrderByClause |
::= | ("order" "by" | "stable" "order" "by")
OrderSpecList |
[48] | OrderSpecList |
::= | OrderSpec
("," OrderSpec)* |
[49] | OrderSpec |
::= | ExprSingle
OrderModifier |
[50] | 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.
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 $w
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 2.4.1
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.[err:XQ0004][err:XP0006] 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")
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 2.4.2.2 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 $inputvalues
where $i mod 100 = 0
return $x)
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.[err:XQ0004][err:XP0006]
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 type error is
raised.[err:XQ0004][err:XP0006]
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:
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.
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:
If stable
is specified, the
original order of T1 and T2 is preserved in the
tuple stream.
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 $employees 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
$books//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 $books//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 $books//book
stable order by $b/title collation "eng-us",
$b/price descending empty least
return $b
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 $a in distinct-values($books)//author
order by $a
return
<author>
<name>
{ $a/text() }
</name>
<books>
{
for $b in $books//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>
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, $s/suppno }
</ps>
)
XQuery supports a conditional expression based on the
keywords if
, then
, and
else
.
[54] | IfExpr |
::= | "if" "(" Expr ")"
"then" ExprSingle
"else" ExprSingle |
The expression following the if
keyword is
called the test expression, and the expressions
following the then
and else
keywords are called the then-expression and
else-expression, respectively.
The first step in processing a conditional expression is to find the effective boolean value of the test expression, as defined in 2.4.2.2 Effective Boolean Value.
The value of a conditional expression is defined as
follows: If the effective boolean value of the test
expression is true
, the value of the
then-expression is returned. If the effective boolean value
of the test expression is false
, the value of
the else-expression is returned.
Conditional expressions have a special rule for
propagating dynamic errors. If the effective
value of the test expression is true
, the
conditional expression ignores (does not raise) any dynamic
errors encountered in the else-expression. In this case,
since the else-expression can have no observable effect, it
need not be evaluated. Similarly, if the effective value of
the test expression is false
, the conditional
expression ignores any dynamic errors encountered in the
then-expression, and the then-expression need not be
evaluated.
Here are some examples of conditional expressions:
In this example, the test expression is a comparison expression:
if ($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 $part/retail
Quantified expressions support existential and universal
quantification. The value of a quantified expression is
always true
or false
.
[51] | QuantifiedExpr |
::= | (("some" "$") | ("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 2.4.2.2 Effective Boolean
Value. The value of the quantified expression is
defined by the following rules:
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
.
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 2.4.1 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.[err:XQ0004][err:XP0006]
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 $x * 2 = 4
In addition to
their use in function parameters and results,
SequenceTypes are used in instance of
,
typeswitch
,
cast
, castable
, and
treat
expressions.
[57] | InstanceofExpr |
::= | TreatExpr (
"instance" "of" SequenceType )? |
The boolean operator instance of
returns
true
if the value of its first operand
matches the type named in its second operand, according
to the rules for SequenceType Matching; otherwise
it returns false
. For example:
5 instance of xs:integer
This example returns true
because the
given value is an instance of the given type.
5 instance of xs:decimal
This example returns true
because the
given value is an integer literal, and
xs:integer
is derived by restriction
from xs:decimal
.
<a>{5}</a> instance of
xs:integer
This example returns false
because
the given value is not an integer; instead, it is an
element containing an integer.
<a>{5}</a> instance of
element(*, xs:integer)
This example returns true
if the
validation process on the constructed element is
successful and the schema definition for element
a
calls for content of type
xs:integer
.
. instance of element()
This example returns true
if the
context item is an element node.
[52] | TypeswitchExpr |
::= | "typeswitch" "(" Expr ")" CaseClause+ "default" ("$"
VarName)? "return"
ExprSingle |
[53] | 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"
[60] | CastExpr |
::= | ComparisonExpr ( "cast"
"as" SingleType
)? |
[123] | 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/type
namespace. The semantics of the cast
expression are as follows:
Atomization is performed on the input expression.
If the result of atomization is a sequence of more than one atomic value, a type error is raised.[err:XQ0004][err:XP0006]
If the result of atomization is an empty sequence:
If ?
is specified after the
target type, the result of the cast
expression is an empty sequence.
If ?
is not specified after the
target type, a type error is
raised.[err:XQ0004][err:XP0006]
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.
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].
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
.
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 [err:XP0029] 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[err:XP0029] is raised if the
resulting value does not satisfy all the facets
of the target type.
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.
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.
For any combination of input type and target
type that is not in the above list, a
cast
expression raises a type
error.[err:XQ0004][err:XP0006]
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.[err:XP0021] 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.
[59] | 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 $x cast as xs:string
Constructor functions provide an alternative syntax for casting.
For every built-in atomic type T that is
defined in [XML Schema], as well
as the predefined types xdt:dayTimeDuration
,
xdt:yearMonthDuration
, and
xdt:untypedAtomic
, a built-in constructor
function is provided. The signature of the built-in
constructor function for type T is as
follows:
T($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 that is in a
namespace, 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) 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
.
User-defined atomic types that are not in a namespace
do not have implicit constructor functions. To construct
an instance of such a type, it is necessary to use a
cast
expression. For example, if the
user-defined type apple
is derived from
xs:integer
but is not in a namespace, an
instance of this type can be constructed as follows:
17 cast as apple
[58] | 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:
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:
If expr1
matches type1
,
using the SequenceType Matching rules in 2.4.1 SequenceType, the
treat
expression returns the value of
expr1
; otherwise, it raises a dynamic
error.[err:XP0006] 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.[err:XP0050]
[77] | ValidateExpr |
::= | "validate" SchemaMode? SchemaContext? "{"
Expr "}" |
/* gn: validate */ |
[12] | SchemaMode |
::= | "lax" | "strict" | "skip" |
|
[78] | SchemaContext |
::= | ("context" SchemaContextLoc) |
"global" |
|
[136] | SchemaContextLoc |
::= | (SchemaContextPath?
QName) | SchemaGlobalTypeName |
|
[135] | 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.[err:XQ0030]
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:
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.[err:XQ0030]
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.[err:XQ0027]
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 definitions.
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> }
[30] | Module |
::= | MainModule |
LibraryModule |
[31] | MainModule |
::= | Prolog QueryBody |
[32] | LibraryModule |
::= | ModuleDecl
Prolog |
[34] | Prolog |
::= | (Version
Separator)? ((NamespaceDecl |
[35] | Separator |
::= | ";" |
[39] | QueryBody |
::= | Expr |
[Definition: A module is a fragment of XQuery code that can independently undergo the analysis phase described in 2.2.3 Expression Processing]. [Definition: A module that contains a Prolog followed by a Query Body is called a main module.] A query has exactly one main module. In a main module, the Query Body can be evaluated, and its value is the result of the query. [Definition: 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 declarations that can be imported into other modules. No module may contain both a module declaration and a Query Body.
[Definition: The Prolog is a series of declarations and imports that create the environment for query processing.] Each declaration or import is followed by a semicolon. 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 imports of schemas and modules, and declarations of namespaces, variables, functions, and various processing options. Declarations and imports may be specified in any order, except that the version declaration, if present, must come first; and variable declarations must avoid circular definitions as described in 4.8 Variable Declaration.
[Definition: The Query Body, if present, consists of an expression that defines the result of the query.] Evaluation of expressions is described in 3 Expressions. A module can be evaluated only if it has a Query Body.
[33] | ModuleDecl |
::= | "module" "namespace" NCName "=" StringLiteral Separator |
A module declaration serves to identify a
module as a library module. A module declaration consists
of the keyword module
followed by a
namespace prefix and a URI that serves as the target
namespace of the module. The names of all variables
and functions declared in a library module must be
explicitly qualified by the target namespace
prefix.[err:XQ0048]
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 declared in the imported modules are added to the static context and (where applicable) to the dynamic context of the importing module.
The following is an example of a module declaration:
module math = "http://example.org/math-functions";
[36] | 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 [err:XQ0031] 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";
[116] | BaseURIDecl |
::= | "declare" "base-uri" StringLiteral |
A base URI declaration specifies the base
URI property of the static context, which is used
when resolving relative URIs within a module. A static error
[err:XQ0032]
is raised if more than one base URI declaration is found
in a query prolog. Note that the fn:doc
function resolves a relative URI using the base URI of
the calling module.
The following is an example of a base URI declaration:
declare base-uri "http://example.org";
[117] | NamespaceDecl |
::= | "declare" "namespace" NCName "=" StringLiteral |
A namespace declaration declares 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.[err:XQ0046] 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.[err:XQ0033] However, a declaration of a namespace in the Prolog can override a prefix that has been predeclared in the static context.
It is a static error [err:XP0008] 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 several predeclared namespace prefixes that
are present in the in-scope namespaces before each
query is processed. These prefixes may be used without an
explicit declaration. They 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 redeclared.) The
predeclared 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
local =
http://www.w3.org/2003/08/xquery-local-functions
(see 4.12 Function
Declaration.)
Additional predeclared 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
redeclared.
[118] | DefaultNamespaceDecl |
::= | (("declare" "default" "element") |
("declare" "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.[err:XQ0046] The following kinds of default namespace declarations are supported:
Declaration of a default element/type namespace declares a namespace URI that is associated with unprefixed names of elements and types. If no default element/type 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:
declare 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/type
namespace within the scope of the constructed
element and its descendants. For example, within the
scope of the following constructed element, the
default element/type 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, the default
function namespace 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:
declare default function namespace "http://example.org/math-functions";
The effect of declaring a default function namespace is that all functions in the default function namespace, including implicitly-declared constructor functions, are aliased with a name that has the original local name, but no namespace URI. The function may then be called 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 (including implicitly-declared constructor functions) in the default function namespace.[err:XP0017]
Unqualified attribute names and variable names are in no namespace.
[142] | SchemaImport |
::= | "import" "schema" SchemaPrefix? StringLiteral ("at"
StringLiteral)? |
[143] | 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/type 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/type namespace for the query:
import schema default element namespace "http://example.org/abc";
It is a static error [err:XQ0035] 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. However, it is not an error for a module to import
the schema with target namespace
http://www.w3.org/2001/XMLSchema
(predeclared prefix xs
), even though the
built-in types defined in this schema are implicitly
included in the in-scope type definitions.
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.
[37] | ModuleImport |
::= | "import" "module" ("namespace" NCName "=")? StringLiteral ("at"
StringLiteral)? |
A module import imports the function
declarations and variable declarations from the Prolog of
a library module into the
in-scope functions and in-scope
variables of the importing module. 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. It is a static error if a module
import does not identify an accessible module to be
imported.[err:XQ0047]
Each module has its own static context. A module import imports only functions and variable declarations; it does not import other objects from the imported module, such as its 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 declarations 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 declared in module C. Two modules may import each other.
It is a type error [err:XQ0036] 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 declarations, function parameters, or function returns found in the imported module. It is a static error [err:XQ0037] to import a module that contains function declarations or variable declarations whose names are already declared 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
declares a function with the function signature
math: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 declared.
The following example illustrates a module import:
import module namespace math = "http://example.org/math-functions";
[38] | VarDecl |
::= | "declare" S
"variable" "$" VarName
TypeDeclaration?
(("{" Expr "}") |
"external") |
[20] | VarName |
::= | QName |
[122] | TypeDeclaration |
::= | "as" SequenceType |
A variable declaration adds the static type of a variable to the in-scope variables, and may also add a value for the variable to the dynamic variables. If the expanded QName of the variable is the same as that of another variable in in-scope variables, a static error is raised.[err:XQ0049]
If a variable declaration includes a type, that type is added to the static context as the type of the variable. If a variable declaration 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 declaration 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.[err:XQ0004]
If a variable declaration includes an expression, the
value of the expression is bound to the variable in the
dynamic context. If the variable declaration 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.[err:XP0006]
If a variable declaration 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 declaration only if that variable or function is declared before the variable declaration (that is, it must be declared or imported earlier in the Prolog than the variable declaration in which it is used.)
All variable names declared in a library module must be explicitly qualified by the namespace prefix of the module's target namespace.[err:XQ0048] When a library module is imported, variables declared in the imported module are added to the in-scope variables of the importing module.
Variable names that have no namespace prefix are in no namespace. Variable declarations that have no namespace prefix may appear only in a main module.
The term variable declaration always refers to a declaration 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 declarations:
The following declaration specifies both the type
and the value of a variable. This declaration 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
dynamic context.
declare variable $x as xs:integer {7};
The following declaration 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.
declare variable $x {7.5};
The following declaration 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 dynamic
context does not have a value of type
xs:integer
, a type error is raised.
declare variable $x as xs:integer external;
The following declaration 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 dynamic context must
include a type and a value for $x
, and
its value must be compatible with its type.
declare variable $x external;
[141] | ValidationDecl |
::= | "declare" "validation" SchemaMode |
[12] | SchemaMode |
::= | "lax" | "strict" | "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.
The following example illustrates a validation declaration:
declare validation strict;
[114] | 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;
[115] | DefaultCollationDecl |
::= | "declare" "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 default collation declaration:
declare 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.[err:XQ0038]
In addition to the built-in functions described in [XQuery 1.0 and XPath 2.0 Functions and Operators], XQuery allows users to declare functions of their own. A function declaration 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 2.4.1 SequenceType. A function declaration causes the declared function to be added to the in-scope functions of the module in which it appears.
[119] | FunctionDecl |
::= | "declare" "function" QName "(" ParamList? (")" | (")" "as"
SequenceType))
(EnclosedExpr |
"external") |
/* gn: parens */ |
[120] | ParamList |
::= | Param (","
Param)* |
|
[121] | Param |
::= | "$" VarName
TypeDeclaration? |
|
[122] | TypeDeclaration |
::= | "as" SequenceType |
A function declaration specifies whether a function is user-defined or external. [Definition: For a user-defined function, the function declaration includes an expression called the function body that defines how the result of the function is computed from its parameters.].
[Definition: External
functions are functions that 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]. External functions are
identified by the keyword external
. The
purpose of a function declaration 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 declared function name in a function declaration must be a QName with a non-empty namespace prefix. If the namespace prefix of a declared function name is empty, a static error is raised.[err:XQ0045] If the expanded QName of the function is the same as that of another function in in-scope functions, a static error is raised.[err:XQ0034]
In order to allow main modules to declare functions
for local use within the module without defining a new
namespace, XQuery predefines the namespace prefix
local
to the namespace
http://www.w3.org/2003/08/xquery-local-functions
,
and reserves this namespace for use in defining local
functions. It is a static error if the declared name
in a function declaration uses one of the predefined
namespace prefixes other than
local
.[err:XQ0045]
If a function parameter is declared using a name but
no type, its default type is item*
. If the
result type is omitted from a function declaration, its
default result type is item*
.
The parameters of a function declaration are considered to be variables whose scope is the function body. It is an static error [err:XQ0039] for a function declaration 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 2.4.1 SequenceType).
The following example illustrates the declaration and
use of a local 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.
declare function local: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> }; local: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 3.1.5 Function Calls
A function declaration may be recursive--that is, it
may reference itself. Mutually recursive functions, whose
bodies reference each other, are also allowed. The
following example declares 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 declaration, the user-declared function
local:depth
calls the built-in functions
empty
and max
, which are in the
default function namespace.
Find the maximum depth of the document named
partlist.xml
.
declare function local: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 $e/* return local:depth($c)) + 1 }; local:depth(doc("partlist.xml"))
In XQuery 1.0, user-declared functions may not be
overloaded. A user-declared function is uniquely
identified by its expanded QName. 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 declared for every user-defined atomic type in the in-scope type definitions, a static error [err:XQ0034] is raised if the Prolog attempts to declare a function with the same expanded QName as any of these types.
Note:
If a future version of XQuery supports overloading of user-declared 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.
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 'gn:' prefix means a 'Grammar Note', and are meant as clarifications for parsing rules, and are explained in A.1.1 Grammar Notes. A 'ws:' prefix explains the white space rules for the production, the details of which are explained in A.2.1 White Space Rules
This section contains general notes on the EBNF productions, which may be helpful in understanding how to create a parser based on this EBNF, how to read the EBNF, and generally call out issues with the syntax. The notes below are referenced from the right side of the production, with the notation: /* gn: <id> */.
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.
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 mandate an implementation strategy for this same effect.)
The ValidateExpr in the exposition, which does not use the "< ... >" token grouping, presents the production in a much simplified, and understandable, form. The ValidateExpr presented in the appendix is technically correct, but structurally hard to understand, because of limitations of the "< ... >" token grouping.
The "/" presents an issue because it occurs both in a leading position and an operator position in expressions. Thus, expressions such as "/ * 5" can easily be confused with the path expression "/*". Therefore, a stand-alone slash, in a leading position, that is followed by an operator, will need to be parenthesized in order to stand alone, as in "(/) * 5". "5 * /", on the other hand, is fine.
Expression comments are allowed inside expressions everywhere that ignorable white space is allowed. Note that expression comments are not allowed in constructor content.
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 preferred .
All keywords are case sensitive.
For readability, White space may be used in most expressions even though not explicitly notated in the EBNF. White space may be freely added between terminals, except a few cases where white space 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 white space or parentheses.
Special white space notation is specified with the EBNF productions, when it is different from the default rules, as follows.
"ws: explicit" means that the EBNF notation must explicitly notate where white space is allowed, otherwise white space may not be freely used.
"ws: significant" means that white space is significant as value content.
For XQuery, White space 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 white space 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.
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 and shows that the tokens listed are recognized when 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 current EBNF production.
Note:
There is no requirement for a lexer/parser to be implemented in terms of lexical states... these are only a declarative way to specify the behavior. The only requirement is to produce results that are consistent with the results of these tables.
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">, QName, "]", ")", <"*" ":" NCName>, "*", StringLiteral, <"typeswitch" "(">, <"declare" "validation"> |
|
||
<"declare" "default" "collation">, <"declare" "namespace">, <"declare" "base-uri">, <"module" "namespace"> |
|
||
<"declare" "default" "element">, <"declare" "default" "function">, <"import" "schema">, <"import" "module"> |
|
||
"$", <"for" "$">, <"let" "$">, <"some" "$">, <"every" "$"> |
|
||
<"declare" S "variable" "$"> |
|
||
<")" "as"> |
|
||
<"element" "(">, <"attribute" "(">, <"comment" "(">, <"text" "(">, <"node" "(">, <"document-node" "("> |
|
||
<"processing-instruction" "("> |
|
||
"<!--" |
|
||
"<?" |
|
||
"<![CDATA[" |
|
||
"<" |
|
||
<"declare" "xmlspace"> |
|
||
"}" |
|
||
<"validate" "{">, <"validate" "global"> |
|
||
<"validate" "context">, <"validate" SchemaMode> |
|
||
<"element" "{">, <"attribute" "{"> |
|
||
<"attribute" QName "{">, <"namespace" NCName "{">, <"element" QName "{">, <"document" "{">, <"text" "{">, <"pi" "{">, <"pi" NCName "{">, <"comment" "{"> |
|
||
<"declare" "function"> |
|
||
"(:" |
|
||
"(::" |
|
||
"{", <"xquery" "version" StringLiteral>, <"at" StringLiteral>, "@", <"ancestor-or-self" "::">, <"ancestor" "::">, <"attribute" "::">, <"child" "::">, <"descendant-or-self" "::">, <"descendant" "::">, <"following-sibling" "::">, <"following" "::">, AxisNamespace, <"parent" "::">, <"preceding-sibling" "::">, <"preceding" "::">, <"self" "::">, ",", <"if" "(">, "[", "(", "-", "+", <QName "(">, ";", QuerySeperator, "//", "/", S |
|
This state is for patterns that are defined for operators.
Pattern | Transition To State | ||
---|---|---|---|
<"declare" "function"> |
|
||
"external", "and", <"at" StringLiteral>, "at", ":=", ",", "div", "else", "=", "except", "eq", "ge", "gt", "le", "lt", "ne", ">=", ">>", ">", "idiv", "global", "intersect", "in", "isnot", "is", "[", "(", "<=", "<<", "<", "-", "mod", "*", "!=", <"order" "by">, "or", "+", "return", "satisfies", ";", QuerySeperator, "//", "/", "then", "to", "union", "|", "where", "{", SchemaMode |
|
||
<"validate" "{"> |
|
||
<"declare" "default" "collation"> |
|
||
<"import" "schema">, <"import" "module">, <"declare" "default" "element">, <"declare" "default" "function"> |
|
||
<"declare" "namespace">, <"declare" "base-uri"> |
|
||
<"instance" "of">, <"castable" "as">, <"cast" "as">, <"treat" "as">, "case", "as", <")" "as"> |
|
||
<"declare" "xmlspace"> |
|
||
"}" |
|
||
"$", <"for" "$">, <"let" "$">, <"some" "$">, <"every" "$"> |
|
||
"(:" |
|
||
"(::" |
|
||
"]", IntegerLiteral, DecimalLiteral, DoubleLiteral, <"typeswitch" "(">, <"stable" "order" "by">, "collation", ")", "ascending", "descending", <"empty" "greatest">, <"empty" "least">, StringLiteral, "default", QName, <NCName ":" "*">, <"*" ":" NCName>, ".", "..", S |
|
This state occurs inside of a namespace declaration, and is needed to recognize a NCName that is to be used as the prefix, as opposed to allowing a QName to occur. (Otherwise, the difference between NCName and QName are ambiguous.)
Pattern | Transition To State | ||
---|---|---|---|
StringLiteral |
|
||
"(:" |
|
||
"(::" |
|
||
"=", NCName, S |
|
This state occurs at places where the keyword "namespace" is expected, which would otherwise be ambiguous compared to a QName. QNames can not occur in this state.
Pattern | Transition To State | ||
---|---|---|---|
StringLiteral, <"at" StringLiteral> |
|
||
"namespace" |
|
||
"(:" |
|
||
"(::" |
|
||
<"default" "element">, <"declare" "default" "element">, <"declare" "default" "function">, S |
|
This state occurs at places where the keywords "preserve" and "strip" is expected to support "declare xmlspace". QNames can not occur in this state.
Pattern | Transition To State | ||
---|---|---|---|
"preserve", "strip" |
|
||
"(:" |
|
||
"(::" |
|
This state distinguishes tokens that can occur only inside the ItemType production.
Pattern | Transition To State | ||
---|---|---|---|
"$" |
|
||
<"empty" "(" ")"> |
|
||
"(:" |
|
||
"(::" |
|
||
<"element" "(">, <"attribute" "(">, <"comment" "(">, <"text" "(">, <"node" "(">, <"document-node" "("> |
|
||
<"processing-instruction" "("> |
|
||
QName, <"item" "(" ")"> |
|
Pattern | Transition To State | ||
---|---|---|---|
"{" |
|
||
<SchemaGlobalContext "/">, SchemaGlobalTypeName |
|
||
")" |
|
||
"*", QName |
|
||
<"element" "("> |
|
||
"@", S, "context", "global", StringLiteral |
|
Pattern | Transition To State | |
---|---|---|
")" |
|
|
S, NCName, StringLiteral |
|
Pattern | Transition To State | |
---|---|---|
")" |
|
|
"," |
|
|
"{" |
|
|
"nillable" |
|
Pattern | Transition To State | ||
---|---|---|---|
NotOccurrenceIndicator |
|
||
"?", "*", "+" |
|
This state distinguishes the SchemaContextStep from the SchemaGlobalContext.
Pattern | Transition To State | |
---|---|---|
<SchemaContextStep "/">, "@" |
|
|
"{" |
|
|
QName |
|
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 |
|
||
"(:" |
|
||
"(::" |
|
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 | ||
---|---|---|---|
"/>" |
|
||
">" |
|
||
'"' |
|
||
"'" |
|
||
"{" |
|
||
S, QName, "=" |
|
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 | ||
---|---|---|---|
"</" |
|
||
"{" |
|
||
"<!--" |
|
||
"<?" |
|
||
"<![CDATA[" |
|
||
"<" |
|
||
PredefinedEntityRef, CharRef, "{{", "}}", ElementContentChar |
|
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 | ||
---|---|---|---|
">" |
|
||
"{" |
|
||
S, QName |
|
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 | |
---|---|---|
"-->" |
|
|
Char, PragmaContents, ExtensionContents |
|
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 | ||
---|---|---|---|
":)", "::)" |
|
||
"(:" |
|
||
"(::" |
|
||
ExprCommentContent |
|
The "(::" token marks the beginning of an expression extension, which must be followed by a keyword.
Pattern | Transition To State | |
---|---|---|
QName, QName |
|
|
"pragma", "extension" |
|
In this state, only lexemes that are legal in a processing instruction name are recognized.
Pattern | Transition To State | |
---|---|---|
PITarget |
|
In this state, only characters are that are legal in processing instruction content are recognized.
Pattern | Transition To State | |
---|---|---|
"?>" |
|
|
Char |
|
In this state, only lexemes that are legal in a CDATA section are recognized.
Pattern | Transition To State | |
---|---|---|
"]]>" |
|
|
Char |
|
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 APOS_ATTRIBUTE_CONTENT, except that apostrophes are allowed without escaping, and an unescaped quote marks the end of the state.
Pattern | Transition To State | ||
---|---|---|---|
'"' |
|
||
"{" |
|
||
EscapeQuot, PredefinedEntityRef, CharRef, "{{", "}}", QuotAttContentChar |
|
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 | ||
---|---|---|---|
"'" |
|
||
"{" |
|
||
EscapeApos, PredefinedEntityRef, CharRef, "{{", "}}", AposAttContentChar |
|
The following is a list of names that must not be used as user function names, in an unprefixed form, because these functions could be confused with expression syntax.
attribute
comment
document-node
element
empty
if
item
node
processing-instruction
text
type
typeswitch
The grammar defines built-in precedence, which is summarised here. In the cases where a number of operators are a choice at the same production level, the expressions are always evaluated from left to right. The operators in order of increasing precedence are:
1 | (comma) |
2 | FLWORExpr, some, every, TypeswitchExpr, IfExpr, or |
3 | and |
4 | instance of |
5 | treat |
6 | castable |
7 | cast |
8 | eq, ne, lt, le, gt, ge, =, !=, <, <=, >, >=, is, isnot, <<, >> |
9 | to |
10 | +, - |
11 | *, div, idiv, mod |
12 | unary -, unary + |
13 | union, | |
14 | intersect, except |
15 | ValidateExpr, /, // |
16 | [ ] |
Under certain circumstances, an atomic value can be promoted from one type to another. Type promotion is used in function calls (see 3.1.5 Function Calls) and in processing of operators that accept numeric operands (listed in the tables below). The following type promotions are permitted:
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.
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
.
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
.)
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 | fn: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* |
Operator | Operand type | Function | Result type |
---|---|---|---|
+ A | numeric | op:numeric-unary-plus(A) | numeric |
- A | numeric | op:numeric-unary-minus(A) | numeric |
The tables in this section describe how values are assigned to the various components of the static context and dynamic context, and to the parameters that control the serialization process.
The following table describes the components of the static context. The following aspects of each component are described:
Default value: This is the value of the component if it is not overridden or augmented by the implementation or by a query.
Can be overwritten or augmented by implementation: Indicates whether an XQuery implementation is allowed to replace the default value of the component by a different value and/or to augment the default value by additional values.
Can be overwritten or augmented by a query: Indicates whether a query is allowed to replace and/or augment the initial value provided by default or by the implementation. If so, indicates how this is accomplished (for example, by a declaration in the prolog).
Scope: Indicates where the component is applicable. "Global" indicates that the component applies throughout a module. "Lexical" indicates that the component applies within the expression in which it is defined (same as "global" if the component is declared in the prolog of a module.)
Consistency Rules: Indicates rules that must be observed in assigning values to the component. If any consistency rule is violated, a static error is raised. Additional consistency rules may be found in 2.2.5 Consistency Constraints.
Component | Default predefined value | Can be overwritten or augmented by implementation? | Can be overwritten or augmented by a query? | Scope | Consistency rules |
---|---|---|---|---|---|
XPath 1.0 Compatability Mode | false | no | no | global | Must be false. |
In-scope namespaces | fn, xml, xs, xsi, xdt, local | overwriteable and augmentable (except for xml) | overwriteable and augmentable by prolog or element constructor | lexical | Only one namespace can be assigned to a given prefix per lexical scope. |
Default element/type namespace | no namespace | overwriteable | overwriteable by prolog or element constructor | lexical | Only one default namespace per lexical scope. |
Default function namespace | fn | overwriteable (not recommended) | overwriteable by prolog | global | Only one declaration per prolog. |
In-scope type definitions | Built-in types in xs, xdt | augmentable | augmentable by schema import in prolog | global | Only one definition per global or local type. |
In-scope element declarations | none | augmentable | augmentable by schema import in prolog | global | Only one definition per global or local element name. |
In-scope attribute declarations | none | augmentable | augmentable by schema import in prolog | global | Only one definition per global or local attribute name. |
In-scope variables | none | augmentable | overwriteable and augmentable by prolog and by variable-binding expressions | lexical | Only one definition per variable per lexical scope. |
In-scope functions | Functions in fn namespace, and constructors for built-in atomic types | augmentable | augmentable by module import and by function declaration in prolog | global | Only one user-declared function with a given name; only one built-in function with a given name and argument cardinality. |
In-scope collations | only the default collation | augmentable | no | global | Each URI uniquely identifies a collation. |
Default collation | Unicode codepoint collation | overwriteable | overwriteable by prolog | global | Only one default collation. |
Validation mode | lax | overwriteable | overwriteable by prolog or validate expression | lexical | Only one validation mode per lexical scope. |
Validation context | global | no | overwriteable by validate expression | lexical | Only one validation context per lexical scope. |
XMLSpace policy | strip | overwriteable | overwriteable by prolog | global | Only one XMLSpace declaration per prolog. |
Base URI | none | overwriteable | overwriteable by prolog | global | Only one base-uri declaration per prolog. |
Statically-known documents | none | augmentable | no | global | None |
Statically-known collections | none | augmentable | no | global | None |
The following table describes the components of the dynamic context. The following aspects of each component are described:
Default value: This is the value of the component if it is not overridden or augmented by the implementation or by a query.
Can be overwritten or augmented by implementation: Indicates whether an XQuery implementation is allowed to replace the default value of the component by a different value and/or to augment the default value by additional values.
Can be overwritten or augmented by a query: Indicates whether a query is allowed to replace and/or augment the initial value provided by default or by the implementation. If so, indicates how this is accomplished.
Scope: Indicates where the component is applicable. "Global" indicates that the component applies throughout a module. "Dynamic" indicates that the value of the component can be influenced by the evaluation of expressions within a query.
Consistency Rules: Indicates rules that must be observed in assigning values to the component. Additional consistency rules may be found in 2.2.5 Consistency Constraints.
Component | Default predefined value | Can be overwritten or augmented by implementation? | Can be overwritten or augmented by a query? | Scope | Consistency rules |
---|---|---|---|---|---|
Context item | none | overwriteable | overwritten during evaluation of path expressions and predicates | dynamic | none |
Context position | none | overwriteable | overwritten during evaluation of path expressions and predicates | dynamic | Must be consistent with context item and context size |
Context size | none | overwriteable | overwritten during evaluation of path expressions and predicates | dynamic | Must be consistent with context item |
Dynamic variables | none | augmentable | overwriteable and augmentable by prolog and by variable-binding expressions | dynamic | Names and values must be consistent with in-scope variables. |
Current date and time | none | Must be initialized by implementation | no | global | Remains constant during evaluation of a query. |
Implicit timezone | none | overwriteable | no | global | Remains constant during evaluation of a query. |
Accessible documents | none | augmentable | no | global | None |
Accessible collections | none | augmentable | no | global | None |
The following table specifies default values for the parameters that control the process of serializing a Data Model instance into XML notation. The meanings of the various parameters are defined in [XSLT 2.0 and XQuery 1.0 Serialization]. For each parameter, an XQuery implementation may (but is not required to) provide a means whereby a user can override the default value.
Parameter | Default Value |
---|---|
encoding | implementation-defined |
cdata-section-elements | empty |
doctype-system | empty |
doctype-public | empty |
escape-uri-attributes | no |
indent | no |
media-type | implementation-defined |
normalize-unicode | implementation-defined |
omit-xml-declaration | yes |
standalone | yes |
character-map | empty |
version | 1.0 |
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. |
Accessible collections. This is a mapping of
strings onto sequences of nodes. The string represents
the absolute URI of a resource. The sequence of nodes
represents the result of the fn:collection
function when that URI is supplied as the argument.
Accessible documents. This is a mapping of
strings onto document nodes. The string represents the
absolute URI of a resource. The document node is the
representation of that resource as an instance of the
data model, as returned by the fn:doc
function when applied to that URI.
A namespace that is declared by a namespace declaration attribute in a direct element constructor, or by a computed namespace constructor inside a computed element constructor, is classified as an active namespace.
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).
Atomization is applied to a value when the
value is used in a context in which 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].
An AttributeTest is used to match an attribute node by its name and/or type.
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 context item is the item currently being processed in a path expression. 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 position is the position of the context item within the sequence of items currently being processed in a path expression.
The context size is the number of items in the sequence of items currently being processed in a path expression.
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.
XQuery operates on the abstract, logical structure of an XML document, rather than its surface syntax. This logical structure is known as the data model, which is defined in the [XQuery 1.0 and XPath 2.0 Data Model] document.
Default collation. This collation is used by string comparison functions when no explicit collation is specified.
Default element/type 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. The initial default function namespace may be provided by the external environmentor by a declaration in the Prolog of a module.
Document order defines a total ordering among all the nodes seen by the language processor and is defined formally in the data model.
The dynamic context of an expression is defined as information that is available at the time the expression is evaluated.
A dynamic error is an error that must be detected during the evaluation phase and may be detected during the analysis phase. Numeric overflow is an example of a dynamic error.
The dynamic evaluation phase is performed only after successful completion of the static analysis phase. The dynamic evaluation phase depends on the operation tree of the expression being evaluated (step DQ1), on the input data (step DQ4), and on the dynamic context (step DQ5), which in turn draws information from the external environment (step DQ3) and the static context (step DQ2).
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 evaluation time its value may have the dynamic type "integer.")
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. The QName is the name of the variable and the value is the dynamic value of the variable.
The effective boolean value of a value is
defined as the result of applying the
fn:boolean
function to the value, as defined
in [XQuery 1.0 and XPath
2.0 Functions and Operators].
An ElementTest is used to match an element node by its name and/or type.
A sequence containing zero items is called an empty sequence.
An error value is a single item or the empty sequence.
The expression context for a given expression consists of all the information that can affect the result of the expression.
External functions are functions that are implemented outside the query environment.
The first three components of the dynamic context (context item, context position, and context size) are called the focus of the expression.
XQuery is a functional language which means that expressions can be nested with full generality. (However, unlike a pure functional language, it does not allow variable substitutability if the variable declaration contains construction of new nodes.)
The function implementation enables the function to map instances of its parameter types into an instance of its result type. For a user-defined function, the function implementation is an XQuery expression. For an external function, the function implementation is implementation dependent.
The function signature specifies the name of the function and the static types of its parameters and its result.
Implementation-defined indicates an aspect that may differ between implementations, but must be specified by the implementor for each particular implementation.
Implementation-dependent indicates an aspect that may differ between implementations, is not specified by this or any W3C specification, and is not required to be specified by the implementor for any particular implementation.
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.
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). If the Schema Import Feature is supported, in-scope attribute declarations include all attribute declarations found in imported schemas.
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.
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). 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 functions. This component defines the set of functions that are available to be called from within an expression. Each function is uniquely identified by its expanded QName and its arity (number of parameters). Each function in in-scope functions has a function signature and a function implementation.
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.
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.
In-scope type definitions. The in-scope type definitions always include the predefined types listed in 2.1.1.1 Predefined Types. If the Schema Import Feature is supported, in-scope type definitions also include all type definitions found in imported schemas.
In-scope variables. This is a set of (QName, type) pairs. It defines the set of variables that are available for reference within an expression. The QName is the name of the variable, and the type is the static type of the variable.
An item is either an atomic value or a node.
A module that contains a module declaration followed by a Prolog is called a library module.
A literal is a direct syntactic representation of an atomic value.
A module that contains a Prolog followed by a Query Body is called a main module.
A module is a fragment of XQuery code that can independently undergo the analysis phase described in 2.2.3 Expression Processing
An implementation may extend XQuery functionality by supporting must-understand extensions. A must-understand extension may be used anywhere that ignorable whitespace is allowed.
A node is an instance of one of the seven node kinds described in [XQuery 1.0 and XPath 2.0 Data Model].
A namespace that is declared in the Prolog, or that is
predefined in the static context, is classified as a
passive namespace, except for the predefined
xml
namespace, which is classified as
active.
A pragma may be used to provide additional information to an XQuery implementation.
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.
The Prolog is a series of declarations and imports that create the environment for query processing.
The Query Body, if present, consists of an expression that defines the result of the query.
A sequence is an ordered collection of zero or more items.
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.
During evaluation 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.
Serialization is the process of converting an instance of the [XQuery 1.0 and XPath 2.0 Data Model] into a sequence of octets (step DM4 in Figure 1.)
A sequence containing exactly one item is called a singleton sequence.
Statically-known collections. This is a mapping
from strings onto types. The string represents the
absolute URI of a resource that is potentially accessible
using the fn:collection
function. The type
is the type of the sequence of nodes that would result
from calling the fn:collection
function with
this URI as its argument.
Statically-known documents. This is a mapping
from strings onto types. The string represents the
absolute URI of a resource that is potentially accessible
using the fn:doc
function. The type is the
type of the document node that would result from calling
the fn:doc
function with this URI as its
argument.
The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on any input data.
The static context of an expression is the information that is available during static analysis of the expression, prior to its evaluation.
A static error is an error that must be detected during the analysis phase. A syntax error is an example of a static error. The means by which static errors are reported during the analysis phase is implementation defined.
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 and XPath 2.0 Formal Semantics].
An XQuery implementation that does not support the Static Typing Feature is not required to raise type errors during the static analysis phase.
The string value of a node is a string and can
be extracted by applying the the fn:string
function to the node. The string value for each kind of
node is defined by the dm:string-value
accessor in [XQuery 1.0 and XPath
2.0 Data Model].
XQuery is also a strongly-typed language in which the operands of various expressions, operators, and functions must conform to the expected types.
Element and attribute nodes have a type annotation, which represents (in an implementation-dependent way) the dynamic (run-time) type of the node.
The typed value of a node is a sequence of
atomic values and can be extracted by applying the
fn:data
function to the node. The typed
value for each kind of node is defined by the
dm:typed-value
accessor in [XQuery 1.0 and XPath 2.0 Data
Model].
A type error may be raised during the analysis or evaluation phase. During the analysis phase, a type error occurs when the static type of an expression does not match the expected type of the context in which the expression occurs. During the evaluation phase, a type error occurs when the dynamic type of a value does not match the expected type of the context in which the value occurs.
For a user-defined function, the function declaration includes an expression called the function body that defines how the result of the function is computed from its parameters.
Validation context. An expression's validation context determines the context in which elements constructed by the expression are validated.
Validation mode. The validation mode specifies
the mode in which validation is performed by element constructors
and by validate
expressions.
XMLSpace policy. This policy, declared in the Prolog, controls the processing of whitespace by element constructors.
XPath 1.0 compatibility mode. This component must be set
by all host languages that include XPath 2.0 as a subset,
indicating whether rules for compatibility with XPath 1.0
are in effect. XQuery sets the value of this component to
false
.
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.
It is a static error if analysis of an expression relies on some component of the static context that has not been assigned a value.
It is a dynamic error if evaluation of an expression relies on some part of the dynamic context that has not been assigned a value.
It is a static error if an expression is not a valid instance of the grammar defined in A.1 EBNF.
During the analysis phase, it is a type error if the static typing feature is in effect and an expression is found to have a static type that is not appropriate for the context in which the expression occurs.
During the analysis phase, it is a type error if the
static typing feature is in effect and the static type
assigned to an expression other than the expression
()
is the empty type.
During the evaluation phase, it is a type error if a value does not match a required type as specified by the matching rules in 2.4.1.1 SequenceType Matching.
It is a type error if the
fn:data
function is applied to a node whose
type annotation denotes a complex type with non-mixed
complex content.
It is a static error if an expression refers to a type name, function name, namespace prefix, or variable name that is not defined in the static context.
An implementation that does not support the Schema Import Feature may raise a static error if a query prolog contains a schema import statement.
An implementation that does not support the Full Axis Feature may raise a static error if a path expression references an unsupported axis (ancestor, ancestor-or-self, following, following-sibling, preceding, or preceding-sibling).
If the Schema Import Feature is in effect, it is a static error if the set of definitions contained in all imported schemas do not satisfy the conditions for schema validity specified in Sections 3 and 5 of [XML Schema] Part 1. In particular, 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.
It is a static error if an implementation supports a pragma and the implementation determines that the PragmaContents are invalid.
It is a static error if an implementation does not support a must-understand extension or an implementation does support a must-understand extension and the implementation determines that the ExtensionContents are invalid.
It is a static error if the XQuery Flagger is enabled and the query contains a must-understand extension.
It is a static error to reference a variable that is not in scope.
It is a static error 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.
It is a static error for an expression to depend on the focus when the focus is undefined.
It is a type error if the result of a step expression (StepExpr) is not a sequence of nodes.
It is a type error if in an axis expression, the context item is not a node.
It is a dynamic error if a value in a cast expression cannot be cast to the required type.
It is a static error if the value of a namespace declaration attribute is not a literal string.
It is a type error if the content sequence in an element constructor contains a document node.
It is a type error if the content sequence in an element constructor contains an attribute node following a node that is not an attribute node or a namespace node.
It is a dynamic error if two or more attribute values in the content sequence of an element constructor have the same name.
In an element-constructor expression, it is a
dynamic
error if the validation mode is strict
and the in-scope element declarations do not
contain an element declaration whose unique name matches
the name of the constructed element.
In an element-constructor or validate expression, it is a dynamic error if validation fails.
It is a type error if the content sequence in a document constructor contains a document, attribute, or namespace node.
It is a dynamic error in a cast expression if the input value does not satisfy the facets of the target type.
It is a type error if the argument of a
validate
expression does not evaluate to
exactly one document or element node.
It is a static error if the version number specified in a version declaration is not supported by the implementation.
A static error is raised if the query prolog contains multiple declarations for the base URI.
It is a static error if the query prolog contains multiple declarations for the same namespace prefix.
It is a static error if more than one function declared or imported by a module has the same expanded QName.
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.
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 declarations, function parameters, or function returns found in the imported module.
It is a static error to import a module that contains function declarations or variable declarations whose names are already declared in the static context of the importing module.
It is a static error if a query prolog specifies more than one default collation, or value specified does not identify a collation known to the implementation.
It is an static error for a function declaration to have more than one parameter with the same name.
It is a type error if the content sequence in an element constructor contains a namespace node node following a node that is not a namespace node.
It is a dynamic error if the name expression in a computed processing instruction or computed namespace constructor returns a QName whose URI part is not empty.
It is a static error if the enclosing expression of a computed namespace constructor is not a computed element constructor.
It is a dynamic error if two or more computed namespace constructors within the same computed element constructor attempt to bind the same namespace prefix.
It is a dynamic error if the name
expression of a computed attribute constructor returns a
string that begins with the characters
xmlns
.
It is a static error if the declared
function name in a function declaration has no namespace
prefix or has one of the predefined namespace prefixes
other than local
.
It is a static error if the URI in a namespace declaration or default namespace declaration is not a valid URI. In addition, the URI in a (non-default) namespace declaration may not be a zero-length string.
It is a static error if the target URI (and location hint, if present) in a module import do not identify an accessible module.
It is a static error if a function or variable declared in a library module is not in the target namespace of the library module.
It is a static error if more than one variable declared or imported by a module has the same expanded QName.
It is a dynamic error if dynamic type of
the operand of a treat
expression does not
match the type specified by the treat
expression.
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.
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:
A document named parts.xml
that
contains many part
elements; each
part
element in turn contains
partno
and description
subelements.
A document named suppliers.xml
that
contains many supplier
elements; each
supplier
element in turn contains
suppno
and suppname
subelements.
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.
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>
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
:
declare function local:precedes($a as node(), $b as node()) as boolean { $a << $b and empty($a//node() intersect $b) };
Similarly, a local:follows
function could
be written:
declare function local:follows($a as node(), $b as node()) as boolean { $a >> $b and empty($b//node() intersect $a) };
Using the local: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 $proc//instrument where local:precedes(($proc//incision)[1], $i) and local:precedes($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 local: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 . << $next-h] } </div>
Note that the above query makes explicit the hierarchy
that was implicit in the original document. In this
example, we assume that the h2
element
containing the text "Introduction" has no
subelements.
Occasionally it is necessary to scan over a hierarchy of elements, applying some transformation at each level of the hierarchy. In XQuery this can be accomplished by defining a recursive function. In this section we will present two examples of such recursive functions.
Suppose that we need to compute a table of contents
for a given document by scanning over the document,
retaining only elements named section
or
title
, and preserving the hierarchical
relationships among these elements. For each
section
, we retain subelements named
section
or title
; but for each
title
, we retain the full content of the
element. This might be accomplished by the following
recursive function:
declare function local:sections-and-titles($n as node()) as node()? { if (local-name($n) = "section") then element { local-name($n) } { for $c in $n/* return local:sections-and-titles($c) } else if (local-name($n) = "title") then $n else ( ) };
The "skeleton" of a given document, containing only
its sections and titles, can then be obtained by invoking
the local:sections-and-titles
function on
the root node of the document, as follows:
local:sections-and-titles(doc("cookbook.xml"))
As another example of a recursive transformation,
suppose that we wish to scan over a document,
transforming every attribute named color
to
an element named color
, and every element
named size
to an attribute named
size
. This can be accomplished by the
following recursive function:
declare function local:swizzle($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 $e/(* | @*) return local:swizzle($c) } case $d as document-node() return document { for $c in $d/* return local:swizzle($c) } default return $n };
The transformation can be applied to a whole document
by invoking the local:swizzle
function on
the root node of the document, as follows:
local:swizzle(doc("plans.xml"))
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 | ||
114 | o-1 | axes | decided | xquery | XPath Axes | ||
328 | 1 | cdata section | decided | xquery | What does CDATA section constructor construct? | ||
257 | D | 1 | collections | decided | xpath | Does collection() always return same result? | |
561 | 1 | conformance | decided | xpath | Normativity of External Mappings | ||
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? | ||
339 | 2 | errors | decided | xquery | Error type for attributes constructed too late | ||
340 | 1 | errors | decided | xpath | How to identify errors? | ||
553 | 1 | errors | decided | xpath | Rules for reporting dynamic errors statically | ||
563 | 1 | errors | decided | xquery | Is dynamic evaluation performed if error in static analysis? | ||
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 | ||
559 | 1 | formal semantics | active | formal-semantics | New Sequence Type needs to be fully implemented in Formal Semantics | ||
558 | 1 | formal semantics | decided | formal-semantics | The content of element types should always allow PI's and comment node types | ||
560 | 1 | formal semantics | decided | formal-semantics | Exactness of Type Inference | ||
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 | decided | formal-semantics | What is in the default context? | ||
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? | ||
499 | 1 | Language | decided | formal-semantics | Casting and validation | ||
510 | 1 | Language | decided | formal-semantics | Is validate working on sequences? | ||
295 | 1 | lexical-representation | decided | xquery | Lexical Representation of Atomic Values | ||
537 | 1 | modules | decided | xquery | What happens to imported schemas that are used in function signatures? | ||
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 | ||
228 | o-2 | namespace functions | decided | xpath | Should we keep the default function namespace, and the xf: namespace? | ||
247 | 2 | namespaces | decided | xpath | What does default namespace(s) affect? | ||
319 | 1 | namespaces | decided | xquery | Namespace definitions and in-scope namespaces | ||
343 | 1 | namespaces | decided | xpath | Do functions in the null namespace clash with functions in the default namespace? | ||
549 | 1 | namespaces | decided | xquery | Computed namespace-constructor | ||
564 | 1 | schema-import | active | xquery | Loading same schema-component twice | ||
528 | 1 | semantics | decided | xpath | Semantics of text constructor on empty sequence | ||
481 | 1 | Semantics | active | formal-semantics | Semantics of Schema Context | ||
496 | 1 | Semantics | active | formal-semantics | Support for lax and strict wildcards | ||
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() | ||
452 | 1 | Semantics | decided | formal-semantics | Semantics of order by | ||
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 | ||
473 | 1 | Semantics | decided | formal-semantics | When to process the query prolog | ||
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 | ||
508 | 1 | Semantics | decided | formal-semantics | Namespaces in element constructors | ||
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 | ||
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? | ||
562 | 1 | static typing | decided | formal-semantics | What static typing for fn:root? | ||
455 | 1 | Static typing | decided | formal-semantics | Typing for the typeswitch default clause | ||
472 | 1 | Static typing | decided | formal-semantics | Static typing of union | ||
475 | 1 | Static typing | decided | formal-semantics | Typing for descendant | ||
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 | ||
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 | ||
547 | 1 | syntax | decided | xquery | Use "declare" for declarations | ||
548 | 1 | syntax | decided | xpath | Lexical Rules: states normative? | ||
550 | 1 | syntax | decided | xquery | Location of Comments | ||
552 | 1 | syntax | decided | xpath | Should the quotes in processing-instruction("...") be optional? | ||
307 | T | 1 | types | active | xpath | Schema Types from input documents? | |
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. | |
526 | 1 | types | decided | xpath | Semantics for anySimpleType and untypedAtomic | ||
527 | 1 | types | decided | formal-semantics | Static typing of XPath index expressions | ||
539 | 1 | types | decided | formal-semantics | Semantics of fs:cast-untypedAtomic in backward compatibility mode | ||
540 | 1 | types | decided | formal-semantics | How does the static semantics works in the case where the input types are unions? | ||
551 | 1 | types | decided | xpath | Constructor functions for unprefixed user defined types | ||
566 | 1 | types | decided | xpath | "treat" should work up and down type hierarchy | ||
524 | 1 | type semantics | decided | xpath | Plural datatypes different from Singular *? | ||
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? | |
523 | 1 | type-semantics | decided | xpath | input(), collection(), document(); validation semantics | ||
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 | ||
534 | 1 | type-semantics | decided | formal-semantics | Semantics of function calls and notion of "expected type" | ||
541 | 1 | type-semantics | decided | formal-semantics | Should it be a static error if an expression other than () has type empty? | ||
542 | 1 | type-semantics | decided | 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? | ||
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 | |
446 | 1 | Typing | decided | formal-semantics | Complexity of interleaving | ||
449 | 1 | Typing | decided | formal-semantics | Constraint on attribute and element content models | ||
486 | 1 | Typing | decided | formal-semantics | Support for PI, comment and namespace nodes | ||
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 |
The data model cannot represent CDATA or CharRef, since the Information Set looses this information.
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.
Decision by: xquery on 2002-12-11 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0317.html (W3C-members only))
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.
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.
Decision by: xsl on 2003-03-07 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Mar/0269.html (W3C-members only))Joint meeting
Decision by: xquery on 2003-03-07 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Mar/0269.html (W3C-members only))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.
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?
Decision by: xquery on 2002-09-04 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Sep/0078.html (W3C-members only))
Decision by: xsl on 2002-10-03 (http://lists.w3.org/Archives/Member/w3c-xsl-wg/2002Oct/0025.html (W3C-members only))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.
XPath supports 13 axes. The current Working Draft says that XQuery will support a subset of these axes, including at least those axes required by the abbreviated syntax. The definitive set of axes to be supported by XQuery has not yet been determined. In the current Working Draft, the examples use abbreviated syntax, but the grammar supports unabbreviated syntax.
For the axes required by the abbreviated syntax, should XQuery allow both the unabbreviated and abbreviated syntax? If we decide not to support additional axes, no new functionality would be added by supporting the unabbreviated syntax. Opinions vary as to whether the unabbreviated syntax is clearer.
Text is in Working Draft 2001-11-28 sec 2.3.
Decision by: xsl on 2002-01-22 (http://lists.w3.org/Archives/Member/w3c-xsl-wg/2002Jan/0067.html (W3C-members only))
Decision by: xquery on 2002-01-23 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Jan/0345.html (W3C-members only))
Acceptance of text in December 2001 published Working Draft.
Decision by: xquery on 2002-07-17 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Jul/0329.html (W3C-members only)) Decided: additional axes will not be included in XQuery Version 1.
The XML Query WG has decided not to support the full set of XPath axes in Version 1. We are trying to keep XQuery small, and that means we want to avoid providing the same functionality in multiple ways unless there is a compelling reason to do so. We also felt that we could easily add the full set of axes in future versions if users clearly demand it.
Experienced XPath users leverage the full set of axes to express complex queries. In examining many XPath expressions, we have found that they can be expressed in XQuery using other features, often using FLWR expressions. The two different approaches use different idioms, and are based on different programming models. We decided not to try to support both models, because it increases the learning required to master the entire language, and increases the probability that distinct user communities will evolve, and they will have difficulty reading each other's queries.
Another reason for not supporting the axes in Version 1 is that they have a lot of semantics, and these can be a burden for an optimizer. An implementation may well be able to do precedes or follows efficiently without an efficient way to perform all the enumerations required by the axes. For instance, an implementation may be able to efficiently determine whether one node is before another node (which means it supports 'precedes' efficiently), yet still have no efficient way of listing all nodes that precede a given node in reverse order (which is required to support the 'preceding' axis). And these axes come in pairs, so an implementation must be able to enumerate the nodes in either document order or reverse document order. Interactions between forward and reverse axes can also be tricky for query optimizers.
We also note that it is easy to write a function library that mimics the axes.
Decision by: xquery on 2003-06-25 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Jul/0031.html (W3C-members only))
Consensus of the XQuery group to make all of the axes (minus namespace) optional as a set (all or nothing).
Section 3.7.5 describes CDATA section constructor, but these cannot be represented in the data model.
Decision by: xquery on 2002-12-11 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0317.html (W3C-members only))
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.
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?
Decision by: xpath-tf on 2002-10-16 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2002Oct/0278.html (W3C-members only))
Decision by: xquery on 2002-10-23 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Oct/0467.html (W3C-members only))
Decision by: xsl on 2002-10-31 (http://lists.w3.org/Archives/Member/w3c-xsl-wg/2002Nov/0004.html (W3C-members only))
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().
Our specifications describe three mappings between the Query Processing environment and the External Processing environment: (1) the Data Model provides optional mappings from a PSVI or Infoset to a Data Model Instance; (2) the Serialization specification provides optional mappings from a Data Model Instance to serialized XML; (3) the Formal Semantics provides optional mappings from an XML Schema to the In-Scope Schema Definitions.
How normative are these mappings?
The following alternatives seem plausible:
1. The mappings are purely informative.
2. Implementations may choose whether to conform to one or more of these mappings, which will be identified by name.
3. As an aid to conformance testing, implementations are required to support a mode in which these mappings are available as specified.
Are there other alternatives we should consider? What are the relative advantages of these approaches?
Decision by: xpath-tf on 2003-07-18 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2003Jul/0092.html (W3C-members only))
The mappings are non-normative.
Are there more processing model options that could make sense as consistent features and thus as conformance levels? What types can these "predefine" in the static context? Do these options have the desired/expected interoperability characteristics?
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).
Decision by: xquery on 2002-09-04 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Sep/0078.html (W3C-members only))
This issue has been addressed by the recent changes to the element constructor.
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?
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).
(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."
Decision by: x-editors on 2003-02-05 (http://lists.w3.org/Archives/Member/w3c-query-editors/2003Feb/0010.html (W3C-members only))
Decision by: xquery on 2003-02-12 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Feb/0242.html (W3C-members only))
Recommend Don's proposal as the closure of this issue.
The fs currently does not model node identity. The position of the formal semantics editors is that a formal semantics need not model everything. So it is not absolutely required that we model node identity, though it would be desirable for us to do so, not least because a clear description of node identity may help clarify the semantics of update. The formal semantics should include a mode of node identity if time permits.
Decision by: xsl on 2003-03-07 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Mar/0269.html (W3C-members only))Joint meeting
Decision by: xquery on 2003-03-07 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Mar/0269.html (W3C-members only))Joint meeting
Decided to define node identity in the Formal Semantics. Required some editorial work to be done.
If there are multiple constructors for the same attribute on an element; which one is taken or is it an error?
Decision by: xquery on 2002-12-11 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0317.html (W3C-members only))
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.
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?
Decision by: xpath-tf on 2002-10-16 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2002Oct/0278.html (W3C-members only))
Decision by: xquery on 2002-10-23 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Oct/0467.html (W3C-members only))
Decision by: xsl on 2002-10-31 (http://lists.w3.org/Archives/Member/w3c-xsl-wg/2002Nov/0004.html (W3C-members only))
This is already covered by the existing spec, but we may want to review the language as part of the actions for issue 257.
Some normative material in XPath/XQuery specifications occurs in more than one location. The specifications need to be clear which of the replicated material is the unique normative definition to ensure ease of implementation and avoid conflicts.
The language book(s) and the Formal Semantics book define together what the semantics of the XQuery 1.0 and XPath 2.0 languages is.
However, there is often duplication (the language book(s) using English while the FS book uses formal notations), and often one document is more specific than the other (for instance the static typing optional feature is mostly described in the FS document). In addition, despite all our hard work some inconsistencies are probably still lurking. Finally, we need to deal with the question about which part of the documents is going to be normative.
Here is a small proposal, laying out a plan to deal with those issues. This plan was discussed at last week's FS editors call, people liked it, and that I was actioned to write it down.
The proposal
(1) For all expressions in the language, the language book should clearly specify in English prose the dynamic semantics of the expression. This English text will serve as the normative version for the dynamic semantics.
(2) For all expressions, the formal semantics book should have dynamic rules which align with (1) above.
(3) For all expressions in the language, the corresponding section in the language book should point to the corresponding FS section which contain the formal rules.
(4) For all expressions, the formal semantics book should have static rules which specify the static semantics of the language. Those formal rules will serve as the normative version for the static semantics.
This plan will obviously require some significant work on our documents, but we believed this would solve all of our alignment/normative problems and improve the quality of our specifications.
Decision by: xpath-tf on 2003-05-14 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2003May/0037.html (W3C-members only))
Decision by: xsl on 2003-05-16 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003May/0176.html (W3C-members only))Joint F2F
Decision by: xquery on 2003-05-16 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003May/0176.html (W3C-members only))Joint F2F
Accepting this general approach and the details with respect to the Formal Semantics. Similar to be worked out for the
"language books" and Datamodel
"language books" and Functions and Operators
Functions and Operators and Formal Semantics
The links that we will put into the documents need to be bi-directional.
What kind of error should be raised by an element constructor in which an attribute is encountered after other element content?
Decision by: xquery on 2002-12-11 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Dec/0317.html (W3C-members only))
This a type error. Type error to be documented in XQuery Section 3.7.2.
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.
Decision by: xpath-tf on 2002-12-17 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2002Dec/0252.html (W3C-members only))
Decision by: xquery on 2002-12-19 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Jan/0167.html (W3C-members only))Joint F2F
Decision by: xsl on 2002-12-19 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Jan/0167.html (W3C-members only))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 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2003Jan/0101.html (W3C-members only))
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 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2003Apr/0075.html (W3C-members only))
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.)
Decision by: xquery on 2003-04-16 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Apr/0247.html (W3C-members only)) with amendment: instead of tying the codes to conformance, we are suggesting to publish these in a non-normative appendix so implementers can use them if see fit
Decision by: xquery on 2003-04-30 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003May/0007.html (W3C-members only))
The XML Query WG has agreed that errors be identified with a code and and some English text as recommended by the I18N folks. The XSL WG has not discussed this yet.
The markup suggested for errors:
<error id="code> English text </error>
seems fine, but we need to decide how to assign the codes.
Jim Melton suggessted 5 or 6 digit fixed length codes partitioned in some manner to indicate the type of error: http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Apr/0259.html
Liam Quin suggested words separated by hyphens: http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Apr/0267.html
Mike Kay would like them to be QNames: unprefixed in the case of codes defined by W3C, namespace-prefixed in the case of implementation-defined or user-defined codes. See http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Apr/0284.html
SUGGESTION ON HOW TO MOVE FORWARD Since the error codes will encompass the language documents, the F&O and possibly the formal semantics we need folks representing all these constituencies to decide on the structure of the error codes and how to partition them. I suggest a small task force to address this. This taskforce would also address the issue of the non-normative appendix and where it should reside.
Under what circumstances can a dynamic error detected early be reported statically, for example if it occurs in code that might not be executed. A host language may determine this, e.g. an <xsl:if> construct.
Decision by: xsl on 2003-05-16 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003May/0176.html (W3C-members only))Joint F2F
Decision by: xquery on 2003-05-16 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003May/0176.html (W3C-members only))Joint F2F
As just a minor addition to the doc is needed and the other addition is the raise of the following other error: a constructor function with a constant argument that is not in the lexical space it was decided to close this issue.
Decision by: xpath-tf on 2003-07-08 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2003Jul/0032.html (W3C-members only))
Adopted the actual text in http://lists.w3.org/Archives/Member/w3c-xsl-query/2003Jun/0087.html.
Decision by: xquery on 2003-07-15 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Jul/0122.html (W3C-members only))Joint meeting.
Decision by: xsl on 2003-07-15 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Jul/0122.html (W3C-members only))Joint meeting.
Wording reviewed and accepted.
Is the dynamic evaluation phase performed only after successful completion of the static analysis phase or whether it can continue even after a static type error.
Proposed Resolution: allowing to continue after static type error can be considered a dynamic typing implementation with a static typing compiler flag (like C's lint). Reason: You would still need to perform dynamic typing. Such an implementation should be possible but not required or even described by the spec.
Proposed resolution:
In 2.2.3.2 Dynamic Evaluation Phase, change current text:
<current_text> The dynamic evaluation phase is performed only after successful completion of the static analysis phase. </current_text>
to:
<new_text> The dynamic evaluation phase occurs after the static analysis phase only if the static analysis phase does not raise any non-type static errors. <xquery_only> If the Static Typing Feature is in effect, dynamic evaluation occurs only if the static analysis phase does not raise any static (non-type and type) errors. </new_text>
Rationale: In the absence of static typing, all type errors must be detected dynamically. Thus, even if a type error is detected statically, it should not prevent dynamic evaluation. However, when static typing is in effect, *all* type errors are static errors, thus any static error should prevent dynamic evaluation.
This resolution requires that static typing behave as it does in other high-level languages. If an implementor wants to provide a "lint-like" feature, they can do so by optionally reporting type errors during static analysis.
Decision by: xquery on 2003-07-15 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Jul/0122.html (W3C-members only))
Mary's text adopted.
Issue: XQuery has not determined what extension mechanisms might be supported. XQuery may support the following:
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.
Decision by: xquery on 2003-03-12 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Mar/0232.html (W3C-members only))
#1 PRAGMAS: Adopted Unanimously.
#2 MUST-UNDERSTAND EXTENSIONS: Adopted.
#3 SEMANTIC EXTENSIONS: Rejected.
#4 FLAGGER: Adopted.
Can (and should) keyword extensions be allowed in XQuery by equipping them with a namespace prefix?
Example:
declare namespace my = http://example.com/myextensions for $e in document ("employees.xml")//employee order by $e/lastname my:fastorder return $e
The advantage of this is that namespaces are a well-established concept for extending vocabularies, and different prefixes may be used for multiple extensions (my:fastorder vs. real:fastorder). The possible disadvantage may be that namespaces are regarded as too clumsy for this purpose.
Note that using namespaces for keyword extensions does not appear to provide a generic mechanism to make the XQuery grammar extensible (one cannot simply allow a sequence of Qnames at arbitrary places without running into ambiguities). An implementation providing some extensions still needs to modify the XQuery grammar accordingly. However this also holds for the other two options, unless "x-" is added to the reserved keywords.
Decision by: xquery on 2003-03-12 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Mar/0232.html (W3C-members only))
The decision for #extension-mechanism also covers this issue.
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.
Decision by: xpath-tf on 2002-12-10 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2002Dec/0164.html (W3C-members only))
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 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Feb/0459.html (W3C-members only))
This issue is also impacted by the following decision:
Decided to adopt 1B and 2A in proposal for issue #xquery-module-syntax.
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.
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.
Decision by: xpath-tf on 2003-03-11 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2003Mar/0206.html (W3C-members only))
Decision by: xquery on 2003-03-19 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Mar/0344.html (W3C-members only))
Proposal accepted.
The content of element types should always allow PI's and comment node types. This is not currently taken into account in the FS document. The best way to deal with that problem is still an open issue. Two possible options are to add PI and comment types during XML Schema import into the XQuery type system (Section 8). Another option is to add PI and comment types during type expansion (judgment expands_to in 7.2.7 Type expansion).
Decision by: fs-editors on 2003-05-01 (http://lists.w3.org/Archives/Member/w3c-query-editors/2003May/0007.html (W3C-members only))
Decision by: xquery on 2003-05-07 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003May/0024.html (W3C-members only))
Fix is in [Section 7.2.6 Type adjustment] which now adds pi and comment types when accessing an element type.
We currently have a couple of static type inference rules (child, descendent) that preserve the more complex type consisting of interleaf, union and sequence. The question is whether this complexity is really needed.
In many cases (such as the FLWR expression used to define /) we just change the inferred type into prime x quantifier.
If we could just infer prime x quantifier, often our inference rules could be simplified.
So the question becomes: Do we really need the more complex and precise types for performing static type checking?
Decision by: xquery on 2003-07-15 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Jul/0122.html (W3C-members only))Joint meeting.
Decision by: xsl on 2003-07-15 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Jul/0122.html (W3C-members only))Joint meeting.
Decided to accept the "Simplified typing" proposal in http://lists.w3.org/Archives/Member/w3c-query-editors/2003Jul/0023.html, which solves this issue.
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.
Decision by: xpath-tf on 2002-10-29 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2002Oct/0449.html (W3C-members only))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 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2002Oct/0511.html (W3C-members only))accepting text for next publication, but keep issue active.
Decision by: xsl on 2002-10-31 (http://lists.w3.org/Archives/Member/w3c-xsl-wg/2002Nov/0004.html (W3C-members only))accepting text for next publication, but keep issue active.
Decision by: xpath-tf on 2003-03-18 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2003Mar/0232.html (W3C-members only))
No adverse public comments received. Close issue with no change.
How do we determine the xml:lang for a node if it inherits xml:lang from a higher-level node?
Decision by: xquery on 2003-02-12 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Feb/0242.html (W3C-members only))
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.
Do we support the sublanguage portion of xml:lang? If so, how?
Decision by: xquery on 2003-02-26 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Feb/0459.html (W3C-members only))
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.
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.
Decision by: xquery on 2003-02-26 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Feb/0459.html (W3C-members only))
Decided to adopt 1B and 2A in proposal for issue #xquery-module-syntax.
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.
Decision by: xquery on 2003-02-26 (http://lists.w3.org/Archives/Member/w3c-xml-query-wg/2003Feb/0459.html (W3C-members only))
Decided to adopt 1B and 2A in proposal for issue #xquery-module-syntax.
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?
Decision by: xpath-tf on 2002-10-29 (http://lists.w3.org/Archives/Member/w3c-xsl-query/2002Oct/0449.html (W3C-members only))as part of Agendum 1.