W3C

XQuery 3.1: An XML Query Language

W3C Proposed Recommendation 17 January 2017

This version:
https://www.w3.org/TR/2017/PR-xquery-31-20170117/
Latest version of XQuery 3.1:
https://www.w3.org/TR/xquery-31/
Previous versions of XQuery 3.1:
https://www.w3.org/TR/2016/CR-xquery-31-20161213/
https://www.w3.org/TR/2015/CR-xquery-31-20151217/
https://www.w3.org/TR/2014/CR-xquery-31-20141218/
https://www.w3.org/TR/2014/WD-xquery-31-20141007/
https://www.w3.org/TR/2014/WD-xquery-31-20140424/
Most recent version of XQuery 3:
https://www.w3.org/TR/xquery-3/
Most recent version of XQuery:
https://www.w3.org/TR/xquery/
Most recent Recommendation of XQuery:
https://www.w3.org/TR/2014/REC-xquery-30-20140408/
Editors:
Jonathan Robie, EMC Corporation <jonathan.robie@emc.com>
Michael Dyck, Invited Expert <jmdyck@ibiblio.org>
Josh Spiegel, Oracle Corporation <josh.spiegel@oracle.com>

See also translations.

This document is also available in these non-normative formats: XML and Change markings relative to previous edition.


Abstract

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

JSON is a lightweight data-interchange format that is widely used to exchange data on the web and to store data in databases. Many applications use JSON together with XML and HTML. XQuery 3.1 extends XQuery to support JSON as well as XML, adding maps and arrays to the data model and supporting them with new expressions in the language and new functions in [XQuery and XPath Functions and Operators 3.1]. A list of changes made since XQuery 3.1 can be found in K Change Log. These are the most important new features in XQuery 3.1:

  1. 3.11.1 Maps.

  2. 3.11.2 Arrays.

Status of this Document

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 https://www.w3.org/TR/.

This document is governed by the 1 September 2015 W3C Process Document.

This is a Proposed Recommendation as described in the Process Document. This document will remain a Proposed Recommendation until 28 February 2017. Advisory Committee Representatives should consult their WBS questionnaires. It was developed by the W3C XML Query Working Group, which is part of the XML Activity. The Working Group expects to advance this specification to Recommendation Status.

This Proposed Recommendation specifies XQuery version 3.1, a fully compatible extension of XQuery version 3.0.

A Test Suite has been created for this document. Implementors are encouraged to run this test suite and report their results. The Test Suite can be found at https://dev.w3.org/2011/QT3-test-suite/. An implementation report is available.

No substantive changes have been made to this specification since its publication as a Candidate Recommendation.

Please report errors in this document using W3C's public Bugzilla system (instructions can be found at https://www.w3.org/XML/2005/04/qt-bugzilla). If access to that system is not feasible, you may send your comments to the W3C XSLT/XPath/XQuery public comments mailing list, public-qt-comments@w3.org. It will be very helpful if you include the string “[XQuery31]” in the subject line of your report, whether made in Bugzilla or in email. Please use multiple Bugzilla entries (or, if necessary, multiple email messages) if you have more than one comment to make. Archives of the comments and responses are available at https://lists.w3.org/Archives/Public/public-qt-comments/.

Publication as a Proposed Recommendation 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.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.


1 Introduction

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

As increasing amounts of JSON are used for lightweight data-exchange, an XML query language for Web data needs to handle JSON as well as XML and HTML.

XQuery is designed to meet the requirements identified by the W3C XML Query Working Group [XQuery 3.1 Requirements]. 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 non-XML 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 [XML Path Language (XPath) Version 1.0], XQL [XQL], XML-QL [XML-QL], SQL [SQL], and OQL [ODMG].

[Definition: XQuery 3.1 operates on the abstract, logical structure of an XML document or JSON object, rather than its surface syntax. This logical structure, known as the data model, is defined in [XQuery and XPath Data Model (XDM) 3.1].]

XQuery 3.1 is an extension of XPath 3.1. In general, any expression that is syntactically valid and executes successfully in both XPath 3.1 and XQuery 3.1 will return the same result in both languages. There are a few exceptions to this rule:

Because 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 3.1 also depends on and is closely related to the following specifications:

[Definition: An XQuery 3.1 Processor processes a query according to the XQuery 3.1 specification. ] [Definition: An XQuery 3.0 Processor processes a query according to the XQuery 3.0 specification. ] [Definition: An XQuery 1.0 Processor processes a query according to the XQuery 1.0 specification. ]

This document specifies a grammar for XQuery 3.1, using the same basic EBNF notation used in [XML 1.0]. Unless otherwise noted (see A.2 Lexical structure), whitespace is not significant in queries. Grammar productions are introduced together with the features that they describe, and a complete grammar is also presented in the appendix [A XQuery 3.1 Grammar]. The appendix is the normative version.

In the grammar productions in this document, named symbols are underlined and literal text is enclosed in double quotes. For example, the following productions describe the syntax of a static function call:

[137]    FunctionCall    ::=    EQName ArgumentList /* xgc: reserved-function-names */
/* gn: parens */
[122]    ArgumentList    ::=    "(" (Argument ("," Argument)*)? ")"

The productions should be read as follows: A function call consists of an EQName followed by an ArgumentList. The argument list consists of an opening parenthesis, an optional list of one or more arguments (separated by commas), and a closing parenthesis.

This document normatively defines the static and dynamic semantics of XQuery 3.1. In this document, examples and material labeled as "Note" are provided for explanatory purposes and are not normative.

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

2 Basics

The basic building block of XQuery 3.1 is the expression, which is a string of [Unicode] characters; the version of Unicode to be used is implementation-defined. The language provides several kinds of expressions which may be constructed from keywords, symbols, and operands. In general, the operands of an expression are other expressions. XQuery 3.1 allows expressions to be nested with full generality. (However, unlike a pure functional language, it does not allow variable substitution if the variable declaration contains construction of new nodes.)

Note:

This specification contains no assumptions or requirements regarding the character set encoding of strings of [Unicode] characters.

Like XML, XQuery 3.1 is a case-sensitive language. Keywords in XQuery 3.1 use lower-case characters and are not reserved—that is, names in XQuery 3.1 expressions are allowed to be the same as language keywords, except for certain unprefixed function-names listed in A.3 Reserved Function Names.

[Definition: In the data model, a value is always a sequence.] [Definition: A sequence is an ordered collection of zero or more items.] [Definition: An item is either an atomic value, a node, or a functionDM31.] [Definition: An atomic value is a value in the value space of an atomic type, as defined in [XML Schema 1.0] or [XML Schema 1.1].] [Definition: A node is an instance of one of the node kinds defined in Section 6 Nodes DM31.] Each node has a unique node identity, a typed value, and a string value. In addition, some nodes have a name. 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.] 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.]

[Definition: The term XDM instance is used, synonymously with the term value, to denote an unconstrained sequence of items.]

Element nodes have a property called in-scope namespaces. [Definition: The in-scope namespaces property of an element node is a set of namespace bindings, each of which associates a namespace prefix with a URI.] For a given element, one namespace binding may have an empty prefix; the URI of this namespace binding is the default namespace within the scope of the element.

Note:

In [XML Path Language (XPath) Version 1.0], the in-scope namespaces of an element node are represented by a collection of namespace nodes arranged on a namespace axis, which is optional and deprecated in [XML Path Language (XPath) Version 3.1]. XQuery does not support the namespace axis and does not represent namespace bindings in the form of nodes.

However, where other specifications such as [XSLT and XQuery Serialization 3.1] refer to namespace nodes, these nodes may be synthesized from the in-scope namespaces of an element node by interpreting each namespace binding as a namespace node. An application that needs to create a set of namespace nodes to represent these bindings for an element bound to $e can do so using the following code.

in-scope-prefixes($e) ! namespace {.}{ namespace-uri-for-prefix(., $e)} 

[Definition: An expanded QName is a triple: its components are a prefix, a local name, and a namespace URI. In the case of a name in no namespace, the namespace URI and prefix are both absent. In the case of a name in the default namespace, the prefix is absent.] When comparing two expanded QNames, the prefixes are ignored: the local name parts must be equal under the Unicode Codepoint Collation, and the namespace URI parts must either both be absent, or must be equal under the Unicode Codepoint Collation.

In the XQuery grammar, QNames representing the names of elements, attributes, functions, variables, types, or other such constructs are written as instances of the grammatical production EQName.

[218]    EQName    ::=    QName | URIQualifiedName
[234]    QName    ::=    [http://www.w3.org/TR/REC-xml-names/#NT-QName]Names /* xgc: xml-version */
[235]    NCName    ::=    [http://www.w3.org/TR/REC-xml-names/#NT-NCName]Names /* xgc: xml-version */
[217]    URILiteral    ::=    StringLiteral
[223]    URIQualifiedName    ::=    BracedURILiteral NCName /* ws: explicit */
[224]    BracedURILiteral    ::=    "Q" "{" (PredefinedEntityRef | CharRef | [^&{}])* "}" /* ws: explicit */

The EQName production allows a QName to be written in one of three ways:

[Definition: A lexical QName is a name that conforms to the syntax of the QName production].

The namespace URI value in a URIQualifiedName is whitespace normalized according to the rules for the xs:anyURI type in Section 3.2.17 anyURI XS1-2 or Section 3.3.17 anyURI XS11-2. It is a static error [err:XQST0070] if the namespace URI for an EQName is http://www.w3.org/2000/xmlns/.

Here are some examples of EQNames:

This document uses the following namespace prefixes to represent the namespace URIs with which they are listed. Although these prefixes are used within this specification to refer to the corresponding namespaces, not all of these bindings will necessarily be present in the static context of every expression, and authors are free to use different prefixes for these namespaces, or to bind these prefixes to different namespaces.

In addition to the prefixes in the above list, this document uses the prefix err to represent the namespace URI http://www.w3.org/2005/xqt-errors (see 2.3.2 Identifying and Reporting Errors). This namespace prefix is not predeclared and its use in this document is not normative. It also uses the namespace URI http://www.w3.org/2012/xquery for which no prefix is used in this document, which is reserved for use in this specification. It is currently used for annotations and option declarations that are defined by the XML Query Working Group.

[Definition: Within this specification, the term URI refers to a Universal Resource Identifier as defined in [RFC3986] and extended in [RFC3987] with the new name IRI.] The term URI has been retained in preference to IRI to avoid introducing new names for concepts such as "Base URI" that are defined or referenced across the whole family of XML specifications.

Note:

In most contexts, processors are not required to raise errors if a URI is not lexically valid according to [RFC3986] and [RFC3987]. See 2.4.5 URI Literals and 3.9.1.2 Namespace Declaration Attributes for details.

2.1 Module Context and Expression Context

[Definition: The expression context for a given expression consists of all the information that can affect the result of the expression.]

[Definition: The module context for a given module consists of all the information that is accessible to top-level expressions in the module.] The context of a top-level expression is defined based on the context of the module in which it is defined: the context of the QueryBody is the context of the main module, and the context for evaluating a function body or for a variable's initializing expression is defined based on the context of the module in which the function or variable is defined.

This information is organized into two categories called the static context and the dynamic context.

2.1.1 Static 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.

The individual components of the static context are described below. Rules governing the initialization and alteration 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 3.1 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: Statically known namespaces. This is a mapping from prefix to namespace URI that defines all the namespaces that are known during static processing of a given expression.] The URI value is whitespace normalized according to the rules for the xs:anyURI type in Section 3.2.17 anyURI XS1-2 or Section 3.3.17 anyURI XS11-2. Note the difference between in-scope namespaces, which is a dynamic property of an element node, and statically known namespaces, which is a static property of an expression.

    Some namespaces are predefined; additional namespaces can be added to the statically known namespaces by namespace declarations, schema imports, or module imports in a Prolog, by a module declaration, and by namespace declaration attributes in direct element constructors.

  • [Definition: Default element/type namespace. This is a namespace URI or absentDM31. The namespace URI, if present, is used for any unprefixed QName appearing in a position where an element or type name is expected.] The URI value is whitespace normalized according to the rules for the xs:anyURI type in Section 3.2.17 anyURI XS1-2 or Section 3.3.17 anyURI XS11-2.

  • [Definition: Default function namespace. This is a namespace URI or absentDM31. The namespace URI, if present, is used for any unprefixed QName appearing in a position where a function name is expected.] The URI value is whitespace normalized according to the rules for the xs:anyURI type in Section 3.2.17 anyURI XS1-2 or Section 3.3.17 anyURI XS11-2.

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

  • [Definition: In-scope variables. This is a mapping from expanded QName to type. It defines the set of variables that are available for reference within an expression. The expanded QName is the name of the variable, and the type is the static type of the variable.]

    Variable declarations in a Prolog are added to in-scope variables. An expression that binds a variable extends the in-scope variables, within the scope of the variable, with the variable and its type. Within the body of an inline function expression or user-defined function , the in-scope variables are extended by the names and types of the function parameters.

    The static type of a variable may either be declared in a query or inferred by static type inference as discussed in 2.2.3.1 Static Analysis Phase.

  • [Definition: Context item static type. This component defines the static type of the context item within the scope of a given expression.]

  • [Definition: Statically known function signatures. This is a mapping from (expanded QName, arity) to function signatureDM31. ] The entries in this mapping define the set of functions that are available to be called from a static function call, or referenced from a named function reference. Each such function is uniquely identified by its expanded QName and arity (number of parameters). Given a statically known function's expanded QName and arity, this component supplies the function's signatureDM31, which specifies various static properties of the function, including types and annotations.

    The statically known function signatures include the signatures of functions from a variety of sources, including the built-in functions, functions declared in the current module (see 4.18 Function Declaration), module imports (see 4.12 Module Import), constructor functions for user-defined types (see 3.18.5 Constructor Functions), and functions provided by an implementation or via an implementation-defined API (see C.1 Static Context Components). It is a static error [err:XQST0034] if two such functions have the same expanded QName and the same arity (even if the signatures are consistent).

  • [Definition: Statically known collations. This is an implementation-defined mapping from URI to collation. It defines the names of the collations that are available for use in processing queries and expressions.] [Definition: A collation is a specification of the manner in which strings and URIs are compared and, by extension, ordered. For a more complete definition of collation, see Section 5.3 Comparison of strings FO31.]

  • [Definition: Default collation. This identifies one of the collations in statically known collations as the collation to be used by functions and operators for comparing and ordering values of type xs:string and xs:anyURI (and types derived from them) when no explicit collation is specified.]

  • [Definition: Construction mode. The construction mode governs the behavior of element and document node constructors. If construction mode is preserve, the type of a constructed element node is xs:anyType, and all attribute and element nodes copied during node construction retain their original types. If construction mode is strip, the type of a constructed element node is xs:untyped; all element nodes copied during node construction receive the type xs:untyped, and all attribute nodes copied during node construction receive the type xs:untypedAtomic.]

  • [Definition: Ordering mode. Ordering mode, which has the value ordered or unordered, affects the ordering of the result sequence returned by certain expressions, as discussed in 3.13 Ordered and Unordered Expressions.]

  • [Definition: Default order for empty sequences. This component controls the processing of empty sequences and NaN values as ordering keys in an order by clause in a FLWOR expression, as described in 3.12.8 Order By Clause.] Its value may be greatest or least.

  • [Definition: Boundary-space policy. This component controls the processing of boundary whitespace by direct element constructors, as described in 3.9.1.4 Boundary Whitespace.] Its value may be preserve or strip.

  • [Definition: Copy-namespaces mode. This component controls the namespace bindings that are assigned when an existing element node is copied by an element constructor, as described in 3.9.1 Direct Element Constructors. Its value consists of two parts: preserve or no-preserve, and inherit or no-inherit.]

  • [Definition: Static Base URI. This is an absolute URI, used to resolve relative URIs both during static analysis and during dynamic evaluation. ] All expressions within a module have the same static base URI. The Static Base URI can be set using a base URI declaration. The Static Base URI is available during dynamic evaluation by use of the fn:static-base-uri function, and is used implicitly during dynamic evaluation by functions such as fn:doc. Relative URI references are resolved as described in 2.4.6 Resolving a Relative URI Reference.

    If the value of the Static Base URI is based on the location of the query module (in the terminology of [RFC3986], the URI used to retrieve the encapsulating entity), then the implementation may use different values for the Static Base URI during static analysis and during dynamic evaluation. This might be necessary, for example, if a query consisting of several modules is compiled, and the resulting object code is distributed to a different location for execution. It would then be inappropriate to use the same location when resolving import module declarations as when retrieving source documents using the fn:doc function. If an implementation uses different values for the Static Base URI during static analysis and during dynamic evaluation, then it is implementation-defined which of the two values is used for particular operations that rely on the Static Base URI; for example, it is implementation-defined which value is used for resolving collation URIs.

  • [Definition: Statically known documents. This is a mapping from strings to types. The string represents the absolute URI of a resource that is potentially available using the fn:doc function. The type is the static type of a call to fn:doc with the given URI as its literal argument. ] If the argument to fn:doc is a string literal that is not present in statically known documents, then the static type of fn:doc is document-node()?.

    Note:

    The purpose of the statically known documents is to provide static type information, not to determine which documents are available. A URI need not be found in the statically known documents to be accessed using fn:doc.

  • [Definition: Statically known collections. This is a mapping from strings to types. The string represents the absolute URI of a resource that is potentially available using the fn:collection function. The type is the type of the sequence of items that would result from calling the fn:collection function with this URI as its argument.] If the argument to fn:collection is a string literal that is not present in statically known collections, then the static type of fn:collection is item()*.

    Note:

    The purpose of the statically known collections is to provide static type information, not to determine which collections are available. A URI need not be found in the statically known collections to be accessed using fn:collection.

  • [Definition: Statically known default collection type. This is the type of the sequence of items that would result from calling the fn:collection function with no arguments.] Unless initialized to some other value by an implementation, the value of statically known default collection type is item()*.

  • [Definition: Statically known decimal formats. This is a mapping from QNames to decimal formats, with one default format that has no visible name, referred to as the unnamed decimal format. Each format is available for use when formatting numbers using the fn:format-number function.]

    Each decimal format defines a set of properties, which control the interpretation of characters in the picture string supplied to the fn:format-number function, and also specify characters to be used in the result of formatting the number.

    The following properties specify characters used both in the picture string, and in the formatted number. In each case the value is a single character:

    • [Definition: decimal-separator is the character used to separate the integer part of the number from the fractional part, both in the picture string and in the formatted number; the default value is the period character (.)]

    • [Definition: exponent-separator is the character used to separate the mantissa from the exponent in scientific notation both in the picture string and in the formatted number; the default value is the character (e).]

    • [Definition: grouping-separator is the character typically used as a thousands separator, both in the picture string and in the formatted number; the default value is the comma character (,)]

    • [Definition: percent is the character used both in the picture string and in the formatted number to indicate that the number is written as a per-hundred fraction; the default value is the percent character (%)]

    • [Definition: per-mille is the character used both in the picture string and in the formatted number to indicate that the number is written as a per-thousand fraction; the default value is the Unicode per-mille character (#x2030)]

    • [Definition: zero-digit is the character used to represent the digit zero; the default value is the Western digit zero (#x30). This character must be a digit (category Nd in the Unicode property database), and it must have the numeric value zero. This property implicitly defines the ten Unicode characters that are used to represent the values 0 to 9: Unicode is organized so that each set of decimal digits forms a contiguous block of characters in numerical sequence. Within the picture string any of these ten character can be used (interchangeably) as a place-holder for a mandatory digit. Within the final result string, these ten characters are used to represent the digits zero to nine.]

    The following properties specify characters to be used in the picture string supplied to the fn:format-number function, but not in the formatted number. In each case the value must be a single character.

    • [Definition: digit is a character used in the picture string to represent an optional digit; the default value is the number sign character (#)]

    • [Definition: pattern-separator is a character used to separate positive and negative sub-pictures in a picture string; the default value is the semi-colon character (;)]

    The following properties specify characters or strings that may appear in the result of formatting the number, but not in the picture string:

    • [Definition: infinity is the string used to represent the double value infinity (INF); the default value is the string "Infinity"]

    • [Definition: NaN is the string used to represent the double value NaN (not-a-number); the default value is the string "NaN"]

    • [Definition: minus-sign is the single character used to mark negative numbers; the default value is the hyphen-minus character (#x2D). ]

2.1.2 Dynamic Context

[Definition: The dynamic context of an expression is defined as information that is needed for the dynamic evaluation of an expression.] If evaluation of an expression relies on some part of the dynamic context that is absentDM31, a dynamic error is raised [err:XPDY0002].

The individual components of the dynamic context are described below. Rules governing the initialization and alteration 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 items are being processed by the expression. If any component in the focus is defined, all components of the focus are defined. [Definition: A singleton focus is a focus that refers to a single item; in a singleton focus, context item is set to the item, context position = 1 and context size = 1.]

Certain language constructs, notably the path operator E1/E2, the simple map operator E1!E2 , and the predicate 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 is used only for the evaluation of E2. Evaluation of E1 continues with its original focus unchanged.

  • [Definition: The context item is the item currently being processed.] [Definition: When the context item is a node, it can also be referred to as the context node.] The context item is returned by an expression consisting of a single dot (.). 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: In the dynamic context of every module in a query, the context item component must have the same setting. If this shared setting is not absentDM31, it is referred to as the initial context item. ]

  • [Definition: The context position is the position of the context item within the sequence of items currently being processed.] It changes whenever the context item changes. When the focus is defined, the value of the context position is 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.] Its value is always an integer greater than zero. The context size is returned by the expression fn: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: Variable values. This is a mapping from expanded QName to value. It contains the same expanded QNames as the in-scope variables in the static context for the expression. The expanded QName is the name of the variable and the value is the dynamic value of the variable, which includes its dynamic type.]

  • [Definition: Named functions. This is a mapping from (expanded QName, arity) to functionDM31. ] It supplies a function for each signature in statically known function signatures and may supply other functions (see 2.2.5 Consistency Constraints). Named functions can include external functions. [Definition: External functions are functions that are implemented outside the query environment.] For example, an implementation might provide a set of implementation-defined external functions in addition to the core function library described in [XQuery and XPath Functions and Operators 3.1]. [Definition: An implementation-defined function is an external function that is implementation-defined ].

  • [Definition: Current dateTime. This information represents an implementation-dependent point in time during the processing of a query, and includes an explicit timezone. It can be retrieved by the fn:current-dateTime function. If invoked multiple times during the execution of a query, this function 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 arithmetic operation. The implicit timezone is an implementation-defined value of type xs:dayTimeDuration. See Section 3.2.7.3 Timezones XS1-2 or Section 3.3.7 dateTime XS11-2 for the range of valid values of a timezone.]

  • [Definition: Default language. This is the natural language used when creating human-readable output (for example, by the functions fn:format-date and fn:format-integer) if no other language is requested. The value is a language code as defined by the type xs:language.]

  • [Definition: Default calendar. This is the calendar used when formatting dates in human-readable output (for example, by the functions fn:format-date and fn:format-dateTime) if no other calendar is requested. The value is a string.]

  • [Definition: Default place. This is a geographical location used to identify the place where events happened (or will happen) when formatting dates and times using functions such as fn:format-date and fn:format-dateTime, if no other place is specified. It is used when translating timezone offsets to civil timezone names, and when using calendars where the translation from ISO dates/times to a local representation is dependent on geographical location. Possible representations of this information are an ISO country code or an Olson timezone name, but implementations are free to use other representations from which the above information can be derived.]

  • [Definition: Available documents. This is a mapping of strings to document nodes. Each string represents the absolute URI of a resource. The document node is the root of a tree that represents that resource using the data model. The document node is returned by the fn:doc function when applied to that URI.] The set of available documents is not limited to the set of statically known documents, and it may be empty.

    If there are one or more URIs in available documents that map to a document node D, then the document-uri property of D must either be absent, or must be one of these URIs.

    Note:

    This means that given a document node $N, the result of fn:doc(fn:document-uri($N)) is $N will always be true, unless fn:document-uri($N) is an empty sequence.

  • [Definition: Available text resources. This is a mapping of strings to text resources. Each string represents the absolute URI of a resource. The resource is returned by the fn:unparsed-text function when applied to that URI.] The set of available text resources is not limited to the set of statically known documents, and it may be empty.

  • [Definition: Available collections. This is a mapping of strings to sequences of items. Each string represents the absolute URI of a resource. The sequence of items represents the result of the fn:collection function when that URI is supplied as the argument. ] The set of available collections is not limited to the set of statically known collections, and it may be empty.

    For every document node D that is in the target of a mapping in available collections, or that is the root of a tree containing such a node, the document-uri property of D must either be absent, or must be a URI U such that available documents contains a mapping from U to D.

    Note:

    This means that for any document node $N retrieved using the fn:collection function, either directly or by navigating to the root of a node that was returned, the result of fn:doc(fn:document-uri($N)) is $N will always be true, unless fn:document-uri($N) is an empty sequence. This implies a requirement for the fn:doc and fn:collection functions to be consistent in their effect. If the implementation uses catalogs or user-supplied URI resolvers to dereference URIs supplied to the fn:doc function, the implementation of the fn:collection function must take these mechanisms into account. For example, an implementation might achieve this by mapping the collection URI to a set of document URIs, which are then resolved using the same catalog or URI resolver that is used by the fn:doc function.

  • [Definition: Default collection. This is the sequence of items that would result from calling the fn:collection function with no arguments.] The value of default collection may be initialized by the implementation.

  • [Definition: Available URI collections. This is a mapping of strings to sequences of URIs. The string represents the absolute URI of a resource which can be interpreted as an aggregation of a number of individual resources each of which has its own URI. The sequence of URIs represents the result of the fn:uri-collection function when that URI is supplied as the argument. ] There is no implication that the URIs in this sequence can be successfully dereferenced, or that the resources they refer to have any particular media type.

    Note:

    An implementation may maintain some consistent relationship between the available collections and the available URI collections, for example by ensuring that the result of fn:uri-collection(X)!fn:doc(.) is the same as the result of fn:collection(X). However, this is not required. The fn:uri-collection function is more general than fn:collection in that it allows access to resources other than XML documents; at the same time, fn:collection allows access to nodes that might lack individual URIs, for example nodes corresponding to XML fragments stored in the rows of a relational database.

  • [Definition: Default URI collection. This is the sequence of URIs that would result from calling the fn:uri-collection function with no arguments.] The value of default URI collection may be initialized by the implementation.

  • [Definition: Environment variables. This is a mapping from names to values. Both the names and the values are strings. The names are compared using an implementation-defined collation, and are unique under this collation. The set of environment variables is implementation-defined and may be empty.]

    Note:

    A possible implementation is to provide the set of POSIX environment variables (or their equivalent on other operating systems) appropriate to the process in which the query is initiated.

2.2 Processing Model

XQuery 3.1 is defined in terms of the data model and the expression context.

Processing                          Model Overview

Figure 1: Processing Model Overview

Figure 1 provides a schematic overview of the processing steps that are discussed in detail below. Some of these steps are completely outside the domain of XQuery 3.1; in Figure 1, these are depicted outside the line that represents the boundaries of the language, an area labeled external processing. The external processing domain includes generation of XDM instances that represent the data to be queried (see 2.2.1 Data Model Generation), schema import processing (see 2.2.2 Schema Import Processing) and serialization (see 2.2.4 Serialization). The area inside the boundaries of the language is known as 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.

2.2.1 Data Model Generation

The input data for a query must be represented as one or more XDM instances. This process occurs outside the domain of XQuery 3.1, which is why Figure 1 represents it in the external processing domain. Here are some steps by which an XML document might be converted to an XDM instance:

  1. 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 1.0 Part 1] or [XML Schema 1.1 Part 1], 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.)

  2. The Information Set or PSVI may be transformed into an XDM instance by a process described in [XQuery and XPath Data Model (XDM) 3.1]. (See DM2 in Fig. 1.)

The above steps provide an example of how an XDM instance might be constructed. An XDM instance might also be synthesized directly from a relational database, or constructed in some other way (see DM3 in Fig. 1.) XQuery 3.1 is defined in terms of the data model, but it does not place any constraints on how XDM instances are constructed.

[Definition: Each element node and attribute node in an XDM instance has a type annotation (described in Section 2.7 Schema Information DM31). The type annotation of a node is a reference to an XML Schema type. ] The type-name of a node is the name of the type referenced by its type annotation. If the XDM instance was derived from a validated XML document as described in Section 3.3 Construction from a PSVI DM31, the type annotations of the element and attribute nodes are derived from schema validation. XQuery 3.1 does not provide a way to directly access the type annotation of an element or attribute node.

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 given the type annotation xs: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 type annotation of an element node indicates how the values in its child text nodes are to be interpreted. An element that has not been validated (such as might occur in a schemaless document) is annotated with the schema type xs:untyped. An element that has been validated and found to be partially valid is annotated with the schema type xs:anyType. If an element node is annotated as xs:untyped, all its descendant element nodes are also annotated as xs:untyped. However, if an element node is annotated as xs:anyType, some of its descendant element nodes may have a more specific type annotation.

2.2.2 Schema Import Processing

The in-scope schema definitions in the static context may be extracted from actual XML schemas (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.

2.2.3 Expression Processing

XQuery 3.1 defines two phases of processing called the static analysis phase and the dynamic evaluation phase (see Fig. 1). During the static analysis phase, static errors, dynamic errors, or type errors may be raised. During the dynamic evaluation phase, only dynamic errors or type errors may be raised. These kinds of errors are defined in 2.3.1 Kinds of Errors.

Within each phase, an implementation is free to use any strategy or algorithm whose result conforms to the specifications in this document.

2.2.3.1 Static Analysis Phase

[Definition: The static analysis phase depends on the expression itself and on the static context. The static analysis phase does not depend on input data (other than schemas).]

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:XPST0003]. 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). If the Schema Aware Feature is supported, the in-scope schema definitions are populated with information from imported schemas. If the Module Feature is supported, the static context is extended with function declarations and variable declarations from imported modules. The static context is used to resolve schema type names, function names, namespace prefixes, and variable names (step SQ4). If a name of one of these kinds in the operation tree is not found in the static context, a static error ([err:XPST0008] or [err:XPST0017]) is raised (however, see exceptions to this rule in 2.5.5.3 Element Test and 2.5.5.5 Attribute Test.)

The operation tree is then normalized by making explicit the implicit operations such as atomization and extraction of Effective Boolean Values (step SQ5).

During the static analysis phase, a processor may perform type analysis. The effect of type analysis is to assign a static type to each expression in the operation tree. [Definition: The static type of an expression is the best inference that the processor is able to make statically about the type of the result of the expression.] This specification does not define the rules for type analysis nor the static types that are assigned to particular expressions: the only constraint is that the inferred type must match all possible values that the expression is capable of returning.

Examples of inferred static types might be:

  • For the expression concat(a,b) the inferred static type is xs:string

  • For the expression $a = $v the inferred static type is xs:boolean

  • For the expression $s[exp] the inferred static type has the same item type as the static type of $s, but a cardinality that allows the empty sequence even if the static type of $s does not allow an empty sequence.

  • The inferred static type of the expression data($x) (whether written explicitly or inserted into the operation tree in places where atomization is implicit) depends on the inferred static type of $x: for example, if $x has type element(*, xs:integer) then data($x) has static type xs:integer.

In XQuery 1.0 and XPath 2.0, rules for static type inferencing were published normatively in [XQuery 1.0 and XPath 2.0 Formal Semantics], but implementations were allowed to refine these rules to infer a more precise type where possible. In XQuery 3.1 and XPath 3.1, the rules for static type inferencing are entirely implementation-dependent.

Every kind of expression also imposes requirements on the type of its operands. For example, with the expression substring($a, $b, $c), $a must be of type xs:string (or something that can be converted to xs:string by the function calling rules), while $b and $c must be of type xs:double.

If the Static Typing Feature is in effect, a processor must raise a type error during static analysis if the inferred static type of an expression is not subsumed by the required type of the context where the expression is used. For example, the call of substring above would cause a type error if the inferred static type of $a is xs:integer; equally, a type error would be reported during static analysis if the inferred static type is xs:anyAtomicType.

If the Static Typing Feature is not in effect, a processor may raise a type error during static analysis only if the inferred static type of an expression has no overlap (intersection) with the required type: so for the first argument of substring, the processor may raise an error if the inferred type is xs:integer, but not if it is xs:anyAtomicType. Alternatively, if the Static Typing Feature is not in effect, the processor may defer all type checking until the dynamic evaluation phase.

2.2.3.2 Dynamic Evaluation Phase

[Definition: The dynamic evaluation phase is the phase during which the value of an expression is computed.] It is dependent on successful completion of the static analysis phase.

The dynamic evaluation phase can occur only if no errors were detected during the static analysis phase. If the Static Typing Feature is in effect, all type errors are detected during static analysis and serve to inhibit the dynamic evaluation 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). The dynamic 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.

[Definition: A dynamic type is associated with each value as it is computed. 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 xs:integer*, denoting a sequence of zero or more integers, but at evaluation time its value may have the dynamic type xs:integer, denoting exactly one 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:XPTY0004].

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

When the Static Typing Feature is in effect, 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 static analysis phase might infer the static type of the function parameter to be an optional element. This case is treated as a type error and inhibits evaluation, even though the function call would have been successful for input data in which the optional element is present.

2.2.4 Serialization

[Definition: Serialization is the process of converting an XDM instance to a sequence of octets (step DM4 in Figure 1.), as described in [XSLT and XQuery Serialization 3.1].]

Note:

This definition of serialization is the definition used in this specification. Any form of serialization that is not based on [XSLT and XQuery Serialization 3.1] is outside the scope of the XQuery 3.1 specification.

Note:

The EXPath Community Group has developed a File Module, which some implementations use to perform file system related operations such as listing, reading, or writing files or directories. Multiple files can be written from a single query.

An XQuery implementation is not required to provide a serialization interface. For example, an implementation may provide only a DOM interface (see [Document Object Model]) or an interface based on an event stream.

[XSLT and XQuery Serialization 3.1] defines a set of serialization parameters that govern the serialization process. If an XQuery implementation provides a serialization interface, it may support (and may expose to users) any of the serialization parameters listed (with default values) in C.1 Static Context Components. If an implementation does not support one of these parameters, it must ignore it without raising an error.

[Definition: An output declaration is an option declaration in the namespace "http://www.w3.org/2010/xslt-xquery-serialization"; it is used to declare serialization parameters.] Except for parameter-document, each option corresponds to a serialization parameter element defined in Section B Schema for Serialization Parameters SER31. The name of each option is the same as the name of the corresponding serialization parameter element, and the values permitted for each option are the same as the values allowed in the serialization parameter element. For QName values, prefixes are expanded to namespace URIs by means of the statically known namespaces, or if unprefixed, the default element/type namespace.

There is no output declaration for use-character-maps, it can be set only by means of a parameter document. When the application requests serialization of the output, the processor may use these parameters to control the way in which the serialization takes place. Processors may also allow external mechanisms for specifying serialization parameters, which may or may not override serialization parameters specified in the query prolog.

The following example illustrates the use of declaration options.

declare namespace output = "http://www.w3.org/2010/xslt-xquery-serialization";
declare option output:method   "xml";
declare option output:encoding "iso-8859-1";
declare option output:indent   "yes";
declare option output:parameter-document "file:///home/me/serialization-parameters.xml";

An output declaration may appear only in a main module; it is a static error [err:XQST0108] if an output declaration appears in a library module. It is a static error [err:XQST0110] if the same serialization parameter is declared more than once. It is a static error [err:XQST0109] if the local name of an output declaration in the http://www.w3.org/2010/xslt-xquery-serialization namespace is not one of the serialization parameter names listed in C.1 Static Context Components or parameter-document, or if the name of an output declaration is use-character-maps. The default value for the method parameter is "xml". An implementation may define additional implementation-defined serialization parameters in its own namespaces.

If the local name of an output declaration in the http://www.w3.org/2010/xslt-xquery-serialization namespace is parameter-document, the value of the output declaration is treated as a URI literal. The value is a location hint, and identifies an XDM instance in an implementation-defined way. If a processor is performing serialization, it is a static error [err:XQST0119] if the implementation is not able to process the value of the output:parameter-document declaration to produce an XDM instance.

If a processor is performing serialization, the XDM instance identified by an output:parameter-document output declaration specifies the values of serialization parameters in the manner defined by Section 3.1 Setting Serialization Parameters by Means of a Data Model Instance SER31. It is a static error [err:XQST0115] if this yields a serialization error. The value of any other output declaration overrides any value that might have been specified for the same serialization parameter using an output declaration in the http://www.w3.org/2010/xslt-xquery-serialization namespace with the local name parameter-document declaration.

A serialization parameter that is not applicable to the chosen output method must be ignored, except that if its value is not a valid value for that parameter, an error may be raised.

A processor that is performing serialization must raise a serialization error if the values of any serialization parameters that it supports (other than any that are ignored under the previous paragraph) are incorrect.

A processor that is not performing serialization may report errors if any serialization parameters are incorrect, or may ignore such parameters.

Specifying serialization parameters in a query does not by itself demand that the output be serialized. It merely defines the desired form of the serialized output for use in situations where the processor has been asked to perform serialization.

Note:

The data model permits an element node to have fewer in-scope namespaces than its parent. Correct serialization of such an element node would require "undeclaration" of namespaces, which is a feature of [XML Names 1.1]. An implementation that does not support [XML Names 1.1] is permitted to serialize such an element without "undeclaration" of namespaces, which effectively causes the element to inherit the in-scope namespaces of its parent.

2.2.5 Consistency Constraints

In order for XQuery 3.1 to be well defined, the input XDM instances, the static context, and the dynamic context must be mutually consistent. The consistency constraints listed below are prerequisites for correct functioning of an XQuery 3.1 implementation. Enforcement of these consistency constraints is beyond the scope of this specification. This specification does not define the result of a query under any condition in which one or more of these constraints is not satisfied.

  • For every node that has a type annotation, if that type annotation is found in the in-scope schema definitions (ISSD), then its definition in the ISSD must be equivalent to its definition in the type annotation.

  • Every element name, attribute name, or schema type name referenced in in-scope variables or statically known function signatures must be in the in-scope schema definitions, unless it is an element name referenced as part of an ElementTest or an attribute name referenced as part of an AttributeTest.

  • Any reference to a global element, attribute, or type name in the in-scope schema definitions must have a corresponding element, attribute or type definition in the in-scope schema definitions.

  • For each mapping of a string to a document node in available 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 2.5.5 SequenceType Matching.

  • For each mapping of a string to a sequence of items in available collections, if there exists a mapping of the same string to a type in statically known collections, the sequence of items must match the type, using the matching rules in 2.5.5 SequenceType Matching.

  • The sequence of items in the default collection must match the statically known default collection type, using the matching rules in 2.5.5 SequenceType Matching.

  • The value of the context item must match the context item static type, using the matching rules in 2.5.5 SequenceType Matching.

  • For each (variable, type) pair in in-scope variables and the corresponding (variable, value) pair in variable values such that the variable names are equal, the value must match the type, using the matching rules in 2.5.5 SequenceType Matching.

  • For each variable declared as external, if the variable declaration does not include a VarDefaultValue, the external environment must provide a value for the variable.

    For each variable declared as external for which the external environment provides a value: If the variable declaration includes a declared type, the value provided by the external environment must match the declared type, using the matching rules in 2.5.5 SequenceType Matching. If the variable declaration does not include a declared type, the external environment must provide a type to accompany the value provided, using the same matching rules.

  • For each function declared as external: the function's implementationDM31 must either return a value that matches the declared result type, using the matching rules in 2.5.5 SequenceType Matching, or raise an implementation-defined error.

  • For a given query, define a participating ISSD as the in-scope schema definitions of a module that is used in evaluating the query. If two participating ISSDs contain a definition for the same schema type, element name, or attribute name, the definitions must be equivalent in both ISSDs. In this context, equivalence means that validating an instance against type T in one ISSD will always have the same effect as validating the same instance against type T in the other ISSD (that is, it will produce the same PSVI, insofar as the PSVI is used during subsequent processing). This means, for example, that the membership of the substitution group of an element declaration in one ISSD must be the same as that of the corresponding element declaration in the other ISSD; that the set of types derived by extension from a given type must be the same; and that in the presence of a strict or lax wildcard, the set of global element (or attribute) declarations capable of matching the wildcard must be the same.

  • In the statically known namespaces, the prefix xml must not be bound to any namespace URI other than http://www.w3.org/XML/1998/namespace, and no prefix other than xml may be bound to this namespace URI. The prefix xmlns must not be bound to any namespace URI, and no prefix may be bound to the namespace URI http://www.w3.org/2000/xmlns/.

  • For each (expanded QName, arity) -> FunctionTest entry in statically known function signatures, there must exist an (expanded QName, arity) -> function entry in named functions such that the function's signatureDM31 is FunctionTest.

2.3 Error Handling

2.3.1 Kinds of Errors

As described in 2.2.3 Expression Processing, XQuery 3.1 defines a static analysis phase, which does not depend on input data, and a dynamic evaluation phase, which does depend on input data. Errors may be raised during each phase.

[Definition: An error that can be detected during the static analysis phase, and is not a type error, is a static error.] A syntax error is an example of a static error.

[Definition: A dynamic error is an error that must be detected during the dynamic evaluation phase and may be detected during the static analysis phase. Numeric overflow is an example of a dynamic error.]

[Definition: A type error may be raised during the static analysis phase or the dynamic evaluation phase. During the static 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 dynamic 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 outcome of the static analysis phase is either success or one or more type errors, static errors, or statically-detected dynamic errors. The result of the dynamic evaluation phase is either a result value, a type error, or a dynamic error.

If more than one error is present, or if an error condition comes within the scope of more than one error defined in this specification, then any non-empty subset of these errors may be reported.

During the static analysis phase, if the Static Typing Feature is in effect and the static type assigned to an expression other than () or data(()) is empty-sequence(), a static error is raised [err:XPST0005]. 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.

Independently of whether the Static Typing Feature is in effect, if an implementation can determine during the static analysis phase that a QueryBody , if evaluated, would necessarily raise a dynamic error or that an expression, if evaluated, would necessarily raise a type error, the implementation may (but is not required to) report that error during the static analysis phase.

An implementation can raise a dynamic error for a QueryBody statically only if the query can never execute without raising that error, as in the following example:

error()

The following example contains a type error, which can be reported statically even if the implementation can not prove that the expression will actually be evaluated.

if (empty($arg))
then
  "cat" * 2
else
  0

[Definition: In addition to static errors, dynamic errors, and type errors, an XQuery 3.1 implementation may raise warnings, either during the static analysis phase or the dynamic 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 for a reason beyond the scope of this specification. For example, limitations may exist on the maximum numbers or sizes of various objects. An error must be raised if such a limitation is exceeded [err:XPDY0130].

2.3.2 Identifying and Reporting Errors

The errors defined in this specification are identified by QNames that have the form err:XXYYnnnn, where:

  • err denotes the namespace for XPath and XQuery errors, http://www.w3.org/2005/xqt-errors. This binding of the namespace prefix err is used for convenience in this document, and is not normative.

  • XX denotes the language in which the error is defined, using the following encoding:

    • XP denotes an error defined by XPath. Such an error may also occur XQuery since XQuery includes XPath as a subset.

    • XQ denotes an error defined by XQuery (or an error originally defined by XQuery and later added to XPath).

  • YY denotes the error category, using the following encoding:

    • ST denotes a static error.

    • DY denotes a dynamic error.

    • TY denotes a type error.

  • nnnn is a unique numeric code.

Note:

The namespace URI for XPath and XQuery errors is not expected to change from one version of XQuery to another. However, the contents of this namespace may be extended to include additional error definitions.

The method by which an XQuery 3.1 processor reports error information to the external environment is implementation-defined.

An error can be represented by a URI reference that is derived from the error QName as follows: an error with namespace URI NS and local part LP can be represented as the URI reference NS # LP . For example, an error whose QName is err:XPST0017 could be represented as http://www.w3.org/2005/xqt-errors#XPST0017.

Note:

Along with a code identifying an error, implementations may wish to return additional information, such as the location of the error or the processing phase in which it was detected. If an implementation chooses to do so, then the mechanism that it uses to return this information is implementation-defined.

2.3.3 Handling Dynamic Errors

Except as noted in this document, if any operand of an expression raises a dynamic error, the expression also raises a dynamic error. If an expression can validly return a value or raise a dynamic error, the implementation may choose to return the value or raise the dynamic error (see 2.3.4 Errors and Optimization). 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.

[Definition: In addition to its identifying QName, a dynamic error may also carry a descriptive string and one or more additional values called error values.] An implementation may provide a mechanism whereby an application-defined error handler can process error values and produce diagnostic messages. XQuery 3.1 provides standard error handling via Section 3.17 Try/Catch Expressions XQ31.

A dynamic error may be raised by a built-in function or operator. For example, the div operator raises an error if its operands are xs:decimal values and its second operand is equal to zero. Errors raised by built-in functions and operators are defined in [XQuery and XPath Functions and Operators 3.1].

A dynamic error can also be raised explicitly by calling the fn:error function, which always raises a dynamic error and never returns a value. This function is defined in Section 3.1.1 fn:error FO31. For example, the following function call raises a dynamic error, providing a QName that identifies the error, a descriptive string, and a diagnostic value (assuming that the prefix app is bound to a namespace containing application-defined error codes):

fn:error(xs:QName("app:err057"), "Unexpected value", fn:string($v))

2.3.4 Errors and Optimization

Because different implementations may choose to evaluate or optimize an expression in different ways, certain aspects of raising dynamic errors are implementation-dependent, as described in this section.

An implementation is always free to evaluate the operands of an operator in any order.

In some cases, a processor can determine the result of an expression without accessing all the data that would be implied by the formal expression semantics. For example, the formal description of filter expressions suggests that $s[1] should be evaluated by examining all the items in sequence $s, and selecting all those that satisfy the predicate position()=1. In practice, many implementations will recognize that they can evaluate this expression by taking the first item in the sequence and then exiting. If $s is defined by an expression such as //book[author eq 'Berners-Lee'], then this strategy may avoid a complete scan of a large document and may therefore greatly improve performance. However, a consequence of this strategy is that a dynamic error or type error that would be detected if the expression semantics were followed literally might not be detected at all if the evaluation exits early. In this example, such an error might occur if there is a book element in the input data with more than one author subelement.

The extent to which a processor may optimize its access to data, at the cost of not raising errors, is defined by the following rules.

Consider an expression Q that has an operand (sub-expression) E. In general the value of E is a sequence. At an intermediate stage during evaluation of the sequence, some of its items will be known and others will be unknown. If, at such an intermediate stage of evaluation, a processor is able to establish that there are only two possible outcomes of evaluating Q, namely the value V or an error, then the processor may deliver the result V without evaluating further items in the operand E. For this purpose, two values are considered to represent the same outcome if their items are pairwise the same, where nodes are the same if they have the same identity, and values are the same if they are equal and have exactly the same type.

There is an exception to this rule: If a processor evaluates an operand E (wholly or in part), then it is required to establish that the actual value of the operand E does not violate any constraints on its cardinality. For example, the expression $e eq 0 results in a type error if the value of $e contains two or more items. A processor is not allowed to decide, after evaluating the first item in the value of $e and finding it equal to zero, that the only possible outcomes are the value true or a type error caused by the cardinality violation. It must establish that the value of $e contains no more than one item.

These rules apply to all the operands of an expression considered in combination: thus if an expression has two operands E1 and E2, it may be evaluated using any samples of the respective sequences that satisfy the above rules.

The rules cascade: if A is an operand of B and B is an operand of C, then the processor needs to evaluate only a sufficient sample of B to determine the value of C, and needs to evaluate only a sufficient sample of A to determine this sample of B.

The effect of these rules is that the processor is free to stop examining further items in a sequence as soon as it can establish that further items would not affect the result except possibly by causing an error. For example, the processor may return true as the result of the expression S1 = S2 as soon as it finds a pair of equal values from the two sequences.

Another consequence of these rules is that where none of the items in a sequence contributes to the result of an expression, the processor is not obliged to evaluate any part of the sequence. Again, however, the processor cannot dispense with a required cardinality check: if an empty sequence is not permitted in the relevant context, then the processor must ensure that the operand is not an empty sequence.

Examples:

  • If an implementation can find (for example, by using an index) that at least one item returned by $expr1 in the following example has the value 47, it is allowed to return true as the result of the some expression, without searching for another item returned by $expr1 that would raise an error if it were evaluated.

    some $x in $expr1 satisfies $x = 47
  • In the following example, if an implementation can find (for example, by using an index) the product element-nodes that have an id child with the value 47, it is allowed to return these nodes as the result of the path expression, without searching for another product node that would raise an error because it has an id child whose value is not an integer.

    //product[id = 47]

For a variety of reasons, including optimization, implementations may rewrite expressions into a different form. There are a number of rules that limit the extent of this freedom:

  • Other than the raising or not raising of errors, the result of evaluating a rewritten expression must conform to the semantics defined in this specification for the original expression.

    Note:

    This allows an implementation to return a result in cases where the original expression would have raised an error, or to raise an error in cases where the original expression would have returned a result. The main cases where this is likely to arise in practice are (a) where a rewrite changes the order of evaluation, such that a subexpression causing an error is evaluated when the expression is written one way and is not evaluated when the expression is written a different way, and (b) where intermediate results of the evaluation cause overflow or other out-of-range conditions.

    Note:

    This rule does not mean that the result of the expression will always be the same in non-error cases as if it had not been rewritten, because there are many cases where the result of an expression is to some degree implementation-dependent or implementation-defined.

  • Conditional, switch, and typeswitch expressions must not raise a dynamic error in respect of subexpressions occurring in a branch that is not selected, and must not return the value delivered by a branch unless that branch is selected. Thus, the following example must not raise a dynamic error if the document abc.xml does not exist:

    if (doc-available('abc.xml')) then doc('abc.xml') else ()

    Of course, the condition must be evaluated in order to determine which branch is selected, and the query must not be rewritten in a way that would bypass evaluating the condition.

  • As stated earlier, an expression must not be rewritten to dispense with a required cardinality check: for example, string-length(//title) must raise an error if the document contains more than one title element.

  • Expressions must not be rewritten in such a way as to create or remove static errors. The static errors in this specification are defined for the original expression, and must be preserved if the expression is rewritten.

Expression rewrite is illustrated by the following examples.

  • Consider the expression //part[color eq "Red"]. An implementation might choose to rewrite this expression as //part[color = "Red"][color eq "Red"]. The implementation might then process the expression as follows: First process the "=" predicate by probing an index on parts by color to quickly find all the parts that have a Red color; then process the "eq" predicate by checking each of these parts to make sure it has only a single color. The result would be as follows:

    • Parts that have exactly one color that is Red are returned.

    • If some part has color Red together with some other color, an error is raised.

    • The existence of some part that has no color Red but has multiple non-Red colors does not trigger an error.

  • The expression in the following example cannot raise a casting error if it is evaluated exactly as written (i.e., left to right). Since neither predicate depends on the context position, an implementation might choose to reorder the predicates to achieve better performance (for example, by taking advantage of an index). This reordering could cause the expression to raise an error.

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

    To avoid unexpected errors caused by expression rewrite, tests that are designed to prevent dynamic errors should be expressed using conditional or typeswitch expressions. For example, the above expression can be written as follows:

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

2.4 Concepts

This section explains some concepts that are important to the processing of XQuery 3.1 expressions.

2.4.1 Document Order

An ordering called document order is defined among all the nodes accessible during processing of a given query, which may consist of one or more trees (documents or fragments). Document order is defined in Section 2.4 Document Order DM31, and its definition is repeated here for convenience. Document order is a total ordering, although the relative order of some nodes is implementation-dependent. [Definition: Informally, document order is the order in which nodes appear in the XML serialization of a document.] [Definition: Document order is stable, which means that the relative order of two nodes will not change during the processing of a given query, even if this order is implementation-dependent.] [Definition: The node ordering that is the reverse of document order is called reverse document order.]

Within a tree, document order satisfies the following constraints:

  1. The root node is the first node.

  2. Every node occurs before all of its children and descendants.

  3. Attribute nodes immediately follow the element node with which they are associated. The relative order of attribute nodes is stable but implementation-dependent.

  4. The relative order of siblings is the order in which they occur in the children property of their parent node.

  5. Children and descendants occur before following siblings.

The relative order of nodes in distinct trees is stable but implementation-dependent, subject to the following constraint: If any node in a given tree T1 is before any node in a different tree T2, then all nodes in tree T1 are before all nodes in tree T2.

2.4.2 Atomization

The semantics of some XQuery 3.1 operators depend on a process called atomization. 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 [err:FOTY0012]FO31. [Definition: Atomization of a sequence is defined as the result of invoking the fn:data function, as defined in Section 2.4 fn:data FO31. ]

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, its typed value is returned (a type error [err:FOTY0012]FO31 is raised if the node has no typed value.)

  • If the item is a functionDM31 (other than an array) or map a type error [err:FOTY0013]FO31 is raised.

  • If the item is an array $a, atomization is defined as $a?* ! fn:data(.), which is equivalent to atomizing the members of the array.

    Note:

    This definition recursively atomizes members that are arrays. Hence, the result of atomizing the array [ [1, 2, 3], [4, 5, 6] ] is the sequence (1, 2, 3, 4, 5, 6).

Atomization is used in processing the following types of expressions:

  • Arithmetic expressions

  • Comparison expressions

  • Function calls and returns

  • Cast expressions

  • Constructor expressions for various kinds of nodes

  • order by clauses in FLWOR expressions

  • group by clauses in FLWOR expressions

  • Switch expressions

2.4.3 Effective Boolean Value

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 Section 7.3.1 fn:boolean FO31.]

The dynamic semantics of fn:boolean are repeated here for convenience:

  1. If its operand is an empty sequence, fn:boolean returns false.

  2. If its operand is a sequence whose first item is a node, fn:boolean returns true.

  3. If its operand is a singleton value of type xs:boolean or derived from xs:boolean, fn:boolean returns the value of its operand unchanged.

  4. If its operand is a singleton value of type xs:string, xs:anyURI, xs:untypedAtomic, or a type derived from one of these, fn:boolean returns false if the operand value has zero length; otherwise it returns true.

  5. If its operand is a singleton value of any numeric type or derived from a numeric type, fn:boolean returns false if the operand value is NaN or is numerically equal to zero; otherwise it returns true.

  6. In all other cases, fn:boolean raises a type error [err:FORG0006]FO31.

    Note:

    For instance, fn:boolean raises a type error if the operand is a function, a map, or an array.

Note:

The effective boolean value of a sequence that contains at least one node and at least one atomic value is implementation-dependent in regions of a query where ordering mode is unordered.

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)

  • WindowStartCondition and WindowEndCondition in window clauses.

Note:

The definition of effective boolean value is not used when casting a value to the type xs:boolean, for example in a cast expression or when passing a value to a function whose expected parameter is of type xs:boolean.

2.4.4 Input Sources

XQuery 3.1 has a set of functions that provide access to XML documents (fn:doc, fn:doc-available), collections (fn:collection, fn:uri-collection), text files (fn:unparsed-text, fn:unparsed-text-lines, fn:unparsed-text-available), and environment variables (fn:environment-variable, fn:available-environment-variables). These functions are defined in Section 14.6 Functions giving access to external information FO31.

An expression can access input data either by calling one of these input functions or by referencing some part of the dynamic context that is initialized by the external environment, such as a variable or context item.

2.4.5 URI Literals

XQuery 3.1 requires a statically known, valid URI in a URILiteral or a BracedURILiteral. An implementation may raise a static error [err:XQST0046] if the value of a URI Literal or a Braced URI Literal is of nonzero length and is neither an absolute URI nor a relative URI.

As in a string literal, any predefined entity reference (such as &amp;), character reference (such as &#x2022;), or EscapeQuot or EscapeApos (for example, "") is replaced by its appropriate expansion. Certain characters, notably the ampersand, can only be represented using a predefined entity reference or a character reference.

Note:

The xs:anyURI type is designed to anticipate the introduction of Internationalized Resource Identifiers (IRI's) as defined in [RFC3987].

Whitespace is normalized using the whitespace normalization rules of fn:normalize-space. If the result of whitespace normalization contains only whitespace, the corresponding URI consists of the empty string. Whitespace normalization is done after the expansion of character references, so writing a newline (for example) as &#xA; does not prevent its being normalized to a space character.

A Braced URI Literal or URI Literal is not subjected to percent-encoding or decoding as defined in [RFC3986].

2.4.6 Resolving a Relative URI Reference

[Definition: To resolve a relative URI $rel against a base URI $base is to expand it to an absolute URI, as if by calling the function fn:resolve-uri($rel, $base).] During static analysis, the base URI is the Static Base URI. During dynamic evaluation, the base URI used to resolve a relative URI reference depends on the semantics of the expression.

Any process that attempts to resolve URI against a base URI, or to dereference the URI, may apply percent-encoding or decoding as defined in the relevant RFCs.

2.5 Types

The type system of XQuery 3.1 is based on [XML Schema 1.0] or [XML Schema 1.1].

[Definition: A sequence type is a type that can be expressed using the SequenceType syntax. Sequence types are used whenever it is necessary to refer to a type in an XQuery 3.1 expression. The term sequence type suggests that this syntax is used to describe the type of an XQuery 3.1 value, which is always a sequence.]

[Definition: A schema type is a type that is (or could be) defined using the facilities of [XML Schema 1.0] or [XML Schema 1.1] (including the built-in types).] A schema type can be used as a type annotation on an element or attribute node (unless it is a non-instantiable type such as xs:NOTATION or xs:anyAtomicType, in which case its derived types can be so used). Every schema type is either a complex type or a simple type; simple types are further subdivided into list types, union types, and atomic types (see [XML Schema 1.0] or [XML Schema 1.1] for definitions and explanations of these terms.)

[Definition: A generalized atomic type is a type which is either (a) an atomic type or (b) a pure union type ].

[Definition: A pure union type is an XML Schema union type that satisfies the following constraints: (1) {variety} is union, (2) the {facets} property is empty, (3) no type in the transitive membership of the union type has {variety} list, and (4) no type in the transitive membership of the union type is a type with {variety} union having a non-empty {facets} property].

Note:

The definition of pure union type excludes union types derived by non-trivial restriction from other union types, as well as union types that include list types in their membership. Pure union types have the property that every instance of an atomic type defined as one of the member types of the union is also a valid instance of the union type.

Note:

The current (second) edition of XML Schema 1.0 contains an error in respect of the substitutability of a union type by one of its members: it fails to recognize that this is unsafe if the union is derived by restriction from another union.

This problem is fixed in XSD 1.1, but the effect of the resolution is that an atomic value labeled with an atomic type cannot be treated as being substitutable for a union type without explicit validation. This specification therefore allows union types to be used as item types only if they are defined directly as the union of a number of atomic types.

Generalized atomic types represent the intersection between the categories of sequence type and schema type. A generalized atomic type, such as xs:integer or my:hatsize, is both a sequence type and a schema type.

2.5.1 Predefined Schema Types

The schema types defined in Section 2.7.2 Predefined Types DM31 are summarized below.

The in-scope schema types in the static context are initialized with certain predefined schema types, including the built-in schema types in the namespace http://www.w3.org/2001/XMLSchema, which has the predefined namespace prefix xs. The schema types in this namespace are defined in [XML Schema 1.0] or [XML Schema 1.1] and augmented by additional types defined in [XQuery and XPath Data Model (XDM) 3.1]. Element and attribute declarations in the xs namespace are not implicitly included in the static context. The schema types defined in [XQuery and XPath Data Model (XDM) 3.1] are summarized below.

  1. [Definition: xs:untyped is used as the type annotation of an element node that has not been validated, or has been validated in skip mode.] No predefined schema types are derived from xs:untyped.

  2. [Definition: xs:untypedAtomic is an atomic type that is used to denote untyped atomic data, such as text that has not been assigned a more specific type.] An attribute that has been validated in skip mode is represented in the data model by an attribute node with the type annotation xs:untypedAtomic. No predefined schema types are derived from xs:untypedAtomic.

  3. [Definition: xs:dayTimeDuration is derived by restriction from xs:duration. The lexical representation of xs:dayTimeDuration is restricted to contain only day, hour, minute, and second components.]

  4. [Definition: xs:yearMonthDuration is derived by restriction from xs:duration. The lexical representation of xs:yearMonthDuration is restricted to contain only year and month components.]

  5. [Definition: xs:anyAtomicType is an atomic type that includes all atomic values (and no values that are not atomic). Its base type is xs:anySimpleType from which all simple types, including atomic, list, and union types, are derived. All primitive atomic types, such as xs:decimal and xs:string, have xs:anyAtomicType as their base type.]

    Note:

    xs:anyAtomicType will not appear as the type of an actual value in an XDM instance.

  6. [Definition: xs:error is a simple type with no value space. It is defined in Section 3.16.7.3 xs:error XS11-1 and can be used in the 2.5.4 SequenceType Syntax to raise errors.]

The relationships among the schema types in the xs namespace are illustrated in Figure 2. A more complete description of the XQuery 3.1 type hierarchy can be found in Section 1.6 Type System FO31.

Type Hierarchy Diagram

Figure 2: Hierarchy of Schema Types used in XQuery 3.1.

2.5.2 Namespace-sensitive Types

[Definition: The namespace-sensitive types are xs:QName, xs:NOTATION, types derived by restriction from xs:QName or xs:NOTATION, list types that have a namespace-sensitive item type, and union types with a namespace-sensitive type in their transitive membership.]

It is not possible to preserve the type of a namespace-sensitive value without also preserving the namespace binding that defines the meaning of each namespace prefix used in the value. Therefore, XQuery 3.1 defines some error conditions that occur only with namespace-sensitive values. For instance, casting to a namespace-sensitive type raises a type error [err:FONS0004]FO31 if the namespace bindings for the result cannot be determined.

2.5.3 Typed Value and String Value

Every node has a typed value and a string value, except for nodes whose value is absentDM31. [Definition: The typed value of a node is a sequence of atomic values and can be extracted by applying the Section 2.4 fn:data FO31 function to the node.] [Definition: The string value of a node is a string and can be extracted by applying the Section 2.3 fn:string FO31 function to the node.]

An implementation may store both the typed value and the string value of a node, or it may store only one of these and derive the other as needed. The string value of a node must be a valid lexical representation of the typed value of the node, but the node is not required to preserve the string representation from the original source document. For example, if the typed value of a node is the xs:integer value 30, its string value might be "30" or "0030".

The typed value, string value, and type annotation of a node are closely related, and are defined by rules found in the following locations:

As a convenience to the reader, the relationship between typed value and string value for various kinds of nodes is summarized and illustrated by examples below.

  1. For text and document nodes, the typed value of the node is the same as its string value, as an instance of the type xs:untypedAtomic. The string value of a document node is formed by concatenating the string values of all its descendant text nodes, in document order.

  2. The typed value of a comment or processing instruction node is the same as its string value. It is an instance of the type xs:string.

  3. The typed value of an attribute node with the type annotation xs:anySimpleType or xs:untypedAtomic is the same as its string value, as an instance of xs:untypedAtomic. The typed value of an attribute node with any other type annotation is derived from its string value and type annotation using the lexical-to-value-space mapping defined in [XML Schema 1.0] or [XML Schema 1.1] Part 2 for the relevant type.

    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 xs:IDREFS, which is a list datatype whose item type is the atomic datatype xs: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 xs: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 xs:IDREFS), its typed value is treated as a sequence of the generalized atomic type from which it is derived (such as xs:IDREF).

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

    1. If the type annotation is xs:untyped or xs:anySimpleType or denotes a complex type with mixed content (including xs:anyType), then the typed value of the node is equal to its string value, as an instance of xs:untypedAtomic. However, if the nilled property of the node is true, then its typed value is the empty sequence.

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

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

      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 from the atomic 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.

      Example: E5 is an element node with the type annotation my:integer-or-string which is a union type with member types xs:integer and xs:string. The string value of E5 is "47". The typed value of E5 is 47 as an xs:integer, since xs:integer is the member type that validated the content of E5. In general, when the type annotation of a node is a union type, the typed value of the node will be an instance of one of the member types of the union.

      Note:

      If an implementation stores only the string value of a node, and the type annotation of the node is a union type, the implementation must be able to deliver the typed value of the node as an instance of the appropriate member type.

    3. If the type annotation denotes a complex type with empty content, then the typed value of the node is the empty sequence and its string value is the zero-length string.

    4. If the type annotation denotes a complex type with element-only content, then the typed value of the node is absentDM31. The fn:data function raises a type error [err:FOTY0012]FO31 when applied to such a node. The string value of such a node is equal to the concatenated string values of all its text node descendants, in document order.

      Example: E6 is an element node with the type annotation weather, which is a complex type whose content type specifies element-only. E6 has two child elements named temperature and precipitation. The typed value of E6 is absentDM31, and the fn:data function applied to E6 raises an error.

2.5.4 SequenceType Syntax

Whenever it is necessary to refer to a type in an XQuery 3.1 expression, the SequenceType syntax is used.

[184]    SequenceType    ::=    ("empty-sequence" "(" ")")
| (ItemType OccurrenceIndicator?)
[186]    ItemType    ::=    KindTest | ("item" "(" ")") | FunctionTest | MapTest | ArrayTest | AtomicOrUnionType | ParenthesizedItemType
[185]    OccurrenceIndicator    ::=    "?" | "*" | "+" /* xgc: occurrence-indicators */
[187]    AtomicOrUnionType    ::=    EQName
[188]    KindTest    ::=    DocumentTest
| ElementTest
| AttributeTest
| SchemaElementTest
| SchemaAttributeTest
| PITest
| CommentTest
| TextTest
| NamespaceNodeTest
| AnyKindTest
[190]    DocumentTest    ::=    "document-node" "(" (ElementTest | SchemaElementTest)? ")"
[199]    ElementTest    ::=    "element" "(" (ElementNameOrWildcard ("," TypeName "?"?)?)? ")"
[201]    SchemaElementTest    ::=    "schema-element" "(" ElementDeclaration ")"
[202]    ElementDeclaration    ::=    ElementName
[195]    AttributeTest    ::=    "attribute" "(" (AttribNameOrWildcard ("," TypeName)?)? ")"
[197]    SchemaAttributeTest    ::=    "schema-attribute" "(" AttributeDeclaration ")"
[198]    AttributeDeclaration    ::=    AttributeName
[200]    ElementNameOrWildcard    ::=    ElementName | "*"
[204]    ElementName    ::=    EQName
[196]    AttribNameOrWildcard    ::=    AttributeName | "*"
[203]    AttributeName    ::=    EQName
[206]    TypeName    ::=    EQName
[194]    PITest    ::=    "processing-instruction" "(" (NCName | StringLiteral)? ")"
[192]    CommentTest    ::=    "comment" "(" ")"
[193]    NamespaceNodeTest    ::=    "namespace-node" "(" ")"
[191]    TextTest    ::=    "text" "(" ")"
[189]    AnyKindTest    ::=    "node" "(" ")"
[207]    FunctionTest    ::=    Annotation* (AnyFunctionTest
| TypedFunctionTest)
[208]    AnyFunctionTest    ::=    "function" "(" "*" ")"
[209]    TypedFunctionTest    ::=    "function" "(" (SequenceType ("," SequenceType)*)? ")" "as" SequenceType
[216]    ParenthesizedItemType    ::=    "(" ItemType ")"
[210]    MapTest    ::=    AnyMapTest | TypedMapTest
[213]    ArrayTest    ::=    AnyArrayTest | TypedArrayTest

With the exception of the special type empty-sequence(), a sequence type consists of an item type that constrains the type of each item in the sequence, and a cardinality that constrains the number of items in the sequence. Apart from the item type item(), which permits any kind of item, item types divide into node types (such as element()), generalized atomic types (such as xs:integer) and function types (such as function() as item()*).

Lexical QNames appearing in a sequence type have their prefixes expanded to namespace URIs by means of the statically known namespaces and (where applicable) the default element/type namespace. Equality of QNames is defined by the eq operator.

Item types representing element and attribute nodes may specify the required type annotations of those nodes, in the form of a schema type. Thus the item type element(*, us:address) denotes any element node whose type annotation is (or is derived from) the schema type named us:address.

The occurrence indicators '+', '*', and '?' bind to the last ItemType in the SequenceType, as described in occurrence-indicators constraint.

Here are some examples of sequence types that might be used in XQuery 3.1:

  • xs:date refers to the built-in atomic schema type named xs:date

  • attribute()? refers to an optional attribute node

  • element() refers to any element node

  • element(po:shipto, po:address) refers to an element node that has the name po:shipto and has the type annotation po:address (or a schema type derived from po:address)

  • element(*, po:address) refers to an element node of any name that has the type annotation po:address (or a type derived from po:address)

  • element(customer) refers to an element node named customer with any type annotation

  • schema-element(customer) refers to an element node whose name is customer (or is in the substitution group headed by customer) and whose type annotation matches the schema type declared for a customer element in the in-scope element declarations

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

  • item()+ refers to a sequence of one or more items

  • function(*) refers to any functionDM31, regardless of arity or type

  • function(node()) as xs:string* refers to a functionDM31 that takes a single argument whose value is a single node, and returns a sequence of zero or more xs:string values

  • (function(node()) as xs:string)* refers to a sequence of zero or more functionsDM31, each of which takes a single argument whose value is a single node, and returns as its result a single xs:string value

2.5.5 SequenceType Matching

[Definition: SequenceType matching compares the dynamic type of a value with an expected sequence type. ] For example, an instance of expression returns true if the dynamic type of a given value matches a given sequence type, or false if it does not.

An XQuery 3.1 implementation must be able to determine relationships among the types in type annotations in an XDM instance and the types in the in-scope schema definitions (ISSD). An XQuery 3.1 implementation must be able to determine relationships among the types in ISSDs used in different modules of the same query.

[Definition: The use of a value whose dynamic type is derived from an expected type is known as subtype substitution.] Subtype substitution does not change the actual type of a value. For example, if an xs:integer value is used where an xs:decimal value is expected, the value retains its type as xs:integer.

The definition of SequenceType matching relies on a pseudo-function named derives-from( AT, ET ), which takes an actual simple or complex schema type AT and an expected simple or complex schema type ET, and either returns a boolean value or raises a type error [err:XPTY0004]. This function is defined as follows:

  • derives-from( AT, ET ) raises a type error [err:XPTY0004] if ET is not present in the in-scope schema definitions (ISSD).

  • derives-from( AT, ET ) returns true if any of the following conditions applies:

    • AT is ET

    • ET is the base type of AT

    • ET is a pure union type of which AT is a member type

    • There is a type MT such that derives-from( AT, MT ) and derives-from( MT, ET )

  • Otherwise, derives-from( AT, ET ) returns false

The rules for SequenceType matching are given below, with examples (the examples are for purposes of illustration, and do not cover all possible cases).

2.5.5.1 Matching a SequenceType and a Value

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

  • ? matches zero or one items

  • * matches zero or more items

  • + matches one or more items

As a consequence of these rules, any sequence type whose OccurrenceIndicator is * or ? matches a value that is an empty sequence.

2.5.5.2 Matching an ItemType and an Item
  • An ItemType consisting simply of an EQName is interpreted as an AtomicOrUnionType. The expected type AtomicOrUnionType matches an atomic value whose actual type is AT if derives-from( AT, AtomicOrUnionType ) is true.

    The name of an AtomicOrUnionType has its prefix expanded to a namespace URI by means of the statically known namespaces, or if unprefixed, the default element/type namespace. If the expanded QName of an AtomicOrUnionType is not defined as a generalized atomic type in the in-scope schema types, a static error is raised [err:XPST0051].

    Example: The ItemType xs:decimal matches any value of type xs:decimal. It also matches any value of type shoesize, if shoesize is an atomic type derived by restriction from xs:decimal.

    Example: Suppose ItemType dress-size is a union type that allows either xs:decimal values for numeric sizes (e.g. 4, 6, 10, 12), or one of an enumerated set of xs:strings (e.g. "small", "medium", "large"). The ItemType dress-size matches any of these values.

    Note:

    The names of non-atomic types such as xs:IDREFS are not accepted in this context, but can often be replaced by a generalized atomic type with an occurrence indicator, such as xs:IDREF+.

  • item() matches any single item.

    Example: item() matches the atomic value 1, the element <a/>, or the function fn:concat#3.

  • 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 PITarget is equal to fn:normalize-space(N). If fn:normalize-space(N) is not in the lexical space of NCName, a type error is raised [err:XPTY0004]

    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 may also be expressed as a string literal, as in this example: processing-instruction("xml-stylesheet").

    If the specified PITarget is not a syntactically valid NCName, a type error is raised [err:XPTY0004].

  • comment() matches any comment node.

  • namespace-node() matches any namespace node.

  • document-node() matches any document node.

  • document-node( E ) matches any document node that contains exactly one element node, optionally accompanied by one or more comment and processing instruction nodes, if E is an ElementTest or SchemaElementTest that matches the element node (see 2.5.5.3 Element Test and 2.5.5.4 Schema Element Test).

    Example: document-node(element(book)) matches a document node containing exactly one element node that is matched by the ElementTest element(book).

  • A ParenthesizedItemType matches an item if and only if the item matches the ItemType that is in parentheses.

  • An ItemType that is an ElementTest, SchemaElementTest, AttributeTest, SchemaAttributeTest, or FunctionTest matches an item as described in the following sections.

  • The ItemType map(K, V) matches an item M if (a) M is a map, and (b) every entry in M has a key that matches K and an associated value that matches V. For example, map(xs:integer, element(employee)) matches a map if all the keys in the map are integers, and all the associated values are employee elements. Note that a map (like a sequence) carries no intrinsic type information separate from the types of its entries, and the type of existing entries in a map does not constrain the type of new entries that can be added to the map.

    Note:

    In consequence, map(K, V) matches an empty map, whatever the types K and V might be.

  • The ItemType map(*) matches any map regardless of its contents. It is equivalent to map(xs:anyAtomicType, item()*).

  • The ItemType array(T) matches any array in which the type of every member is T.

  • The ItemType array(*) matches any array regardless of its contents.

2.5.5.3 Element Test
[199]    ElementTest    ::=    "element" "(" (ElementNameOrWildcard ("," TypeName "?"?)?)? ")"
[200]    ElementNameOrWildcard    ::=    ElementName | "*"
[204]    ElementName    ::=    EQName
[206]    TypeName    ::=    EQName

An ElementTest is used to match an element node by its name and/or type annotation.

The ElementName and TypeName of an ElementTest have their prefixes expanded to namespace URIs by means of the statically known namespaces, or if unprefixed, the default element/type namespace. The ElementName need not be present in the in-scope element declarations, but the TypeName must be present in the in-scope schema types [err:XPST0008]. Note that substitution groups do not affect the semantics of ElementTest.

An ElementTest may take any of the following forms:

  1. element() and element(*) match any single element node, regardless of its name or type annotation.

  2. element( ElementName ) matches any element node whose name is ElementName, regardless of its type annotation or nilled property.

    Example: element(person) matches any element node whose name is person.

  3. element( ElementName , TypeName ) matches an element node whose name is ElementName if derives-from( AT, TypeName ) is true, where AT is the type annotation of the element node, and the nilled property of the node is false.

    Example: element(person, surgeon) matches a non-nilled element node whose name is person and whose type annotation is surgeon (or is derived from surgeon).

  4. element( ElementName, TypeName ?) matches an element node whose name is ElementName if derives-from( AT, TypeName ) is true, where AT is the type annotation of the element node. The nilled property of the node may be either true or false.

    Example: element(person, surgeon?) matches a nilled or non-nilled element node whose name is person and whose type annotation is surgeon (or is derived from surgeon).

  5. element(*, TypeName ) matches an element node regardless of its name, if derives-from( AT, TypeName ) is true, where AT is the type annotation of the element node, and the nilled property of the node is false.

    Example: element(*, surgeon) matches any non-nilled element node whose type annotation is surgeon (or is derived from surgeon), regardless of its name.

  6. element(*, TypeName ?) matches an element node regardless of its name, if derives-from( AT, TypeName ) is true, where AT is the type annotation of the element node. The nilled property of the node may be either true or false.

    Example: element(*, surgeon?) matches any nilled or non-nilled element node whose type annotation is surgeon (or is derived from surgeon), regardless of its name.

2.5.5.4 Schema Element Test
[201]    SchemaElementTest    ::=    "schema-element" "(" ElementDeclaration ")"
[202]    ElementDeclaration    ::=    ElementName
[204]    ElementName    ::=    EQName

A SchemaElementTest matches an element node against a corresponding element declaration found in the in-scope element declarations.

The ElementName of a SchemaElementTest has its prefixes expanded to a namespace URI by means of the statically known namespaces, or if unprefixed, the default element/type namespace. If the ElementName specified in the SchemaElementTest is not found in the in-scope element declarations, a static error is raised [err:XPST0008].

A SchemaElementTest matches a candidate element node if all of the following conditions are satisfied:

  1. Either:

    1. The name N of the candidate node matches the specified ElementName, or

    2. The name N of the candidate node matches the name of an element declaration that is a member of the actual substitution group headed by the declaration of element ElementName.

    Note:

    The term "actual substitution group" is defined in [XML Schema 1.1]. The actual substitution group of an element declaration H includes those element declarations P that are declared to have H as their direct or indirect substitution group head, provided that P is not declared as abstract, and that P is validly substitutable for H, which means that there must be no blocking constraints that prevent substitution.

  2. The schema element declaration named N is not abstract.

  3. derives-from( AT, ET ) is true, where AT is the type annotation of the candidate node and ET is the schema type declared in the schema element declaration named N.

  4. If the schema element declaration named N is not nillable, then the nilled property of the candidate node is false.

Example: The SchemaElementTest schema-element(customer) matches a candidate element node in the following two situations:

  1. customer is a top-level element declaration in the in-scope element declarations; the name of the candidate node is customer; the element declaration of customer is not abstract; the type annotation of the candidate node is the same as or derived from the schema type declared in the customer element declaration; and either the candidate node is not nilled, or customer is declared to be nillable.

  2. customer is a top-level element declaration in the in-scope element declarations; the name of the candidate node is client; client is an actual (non-abstract and non-blocked) member of the substitution group of customer; the type annotation of the candidate node is the same as or derived from the schema type declared for the client element; and either the candidate node is not nilled, or client is declared to be nillable.

2.5.5.5 Attribute Test
[195]    AttributeTest    ::=    "attribute" "(" (AttribNameOrWildcard ("," TypeName)?)? ")"
[196]    AttribNameOrWildcard    ::=    AttributeName | "*"
[203]    AttributeName    ::=    EQName
[206]    TypeName    ::=    EQName

An AttributeTest is used to match an attribute node by its name and/or type annotation.

The AttributeName and TypeName of an AttributeTest have their prefixes expanded to namespace URIs by means of the statically known namespaces. If unprefixed, the AttributeName is in no namespace, but an unprefixed TypeName is in the default element/type namespace. The AttributeName need not be present in the in-scope attribute declarations, but the TypeName must be present in the in-scope schema types [err:XPST0008].

An AttributeTest may take any of the following forms:

  1. attribute() and attribute(*) match any single attribute node, regardless of its name or type annotation.

  2. attribute( AttributeName ) matches any attribute node whose name is AttributeName, regardless of its type annotation.

    Example: attribute(price) matches any attribute node whose name is price.

  3. attribute( AttributeName, TypeName ) matches an attribute node whose name is AttributeName if derives-from( AT, TypeName ) is true, where AT is the type annotation of the attribute node.

    Example: attribute(price, currency) matches an attribute node whose name is price and whose type annotation is currency (or is derived from currency).

  4. attribute(*, TypeName ) matches an attribute node regardless of its name, if derives-from( AT, TypeName ) is true, where AT is the type annotation of the attribute node.

    Example: attribute(*, currency) matches any attribute node whose type annotation is currency (or is derived from currency), regardless of its name.

2.5.5.6 Schema Attribute Test
[197]    SchemaAttributeTest    ::=    "schema-attribute" "(" AttributeDeclaration ")"
[198]    AttributeDeclaration    ::=    AttributeName
[203]    AttributeName    ::=    EQName

A SchemaAttributeTest matches an attribute node against a corresponding attribute declaration found in the in-scope attribute declarations.

The AttributeName of a SchemaAttributeTest has its prefixes expanded to a namespace URI by means of the statically known namespaces. If unprefixed, an AttributeName is in no namespace. If the AttributeName specified in the SchemaAttributeTest is not found in the in-scope attribute declarations, a static error is raised [err:XPST0008].

A SchemaAttributeTest matches a candidate attribute node if both of the following conditions are satisfied:

  1. The name of the candidate node matches the specified AttributeName.

  2. derives-from( AT, ET ) is true, where AT is the type annotation of the candidate node and ET is the schema type declared for attribute AttributeName in the in-scope attribute declarations.

Example: The SchemaAttributeTest schema-attribute(color) matches a candidate attribute node if color is a top-level attribute declaration in the in-scope attribute declarations, the name of the candidate node is color, and the type annotation of the candidate node is the same as or derived from the schema type declared for the color attribute.

2.5.5.7 Function Test
[207]    FunctionTest    ::=    Annotation* (AnyFunctionTest
| TypedFunctionTest)
[208]    AnyFunctionTest    ::=    "function" "(" "*" ")"
[209]    TypedFunctionTest    ::=    "function" "(" (SequenceType ("," SequenceType)*)? ")" "as" SequenceType

A FunctionTest matches a functionDM31, potentially also checking its function signatureDM31 and annotations (see 4.15 Annotations). An AnyFunctionTest matches any item that is a function. A TypedFunctionTest matches an item if it is a functionDM31 and the function's type signature (as defined in Section 2.8.1 Functions DM31) is a subtype of the TypedFunctionTest.

Here are some examples of FunctionTests:

  1. function(*) matches any function, including maps and arrays.

  2. %assertion function(*) matches any functionDM31 if the implementation-defined function assertion %assertion is satisfied.

  3. function(int, int) as int matches any functionDM31 with the function signature function(int, int) as int.

  4. %assertion function(int, int) as int matches any functionDM31 with the function signature function(int, int) as int if the implementation-defined function assertion %assertion is satisfied.

  5. function(xs:anyAtomicType) as item()* matches any map, or any function with the required signature.

  6. function(xs:integer) as item()* matches any array, or any function with the required signature.

[Definition: A function assertion is a predicate that restricts the set of functions matched by a FunctionTest. It uses the same syntax as 4.15 Annotations.] XQuery 3.1 does not currently define any function assertions, but future versions may. Other specifications in the XQuery family may also use function assertions in the future.

Implementations are free to define their own function assertions, whose behavior is completely implementation-defined. Implementations may also provide a way for users to define their own function assertions.

An implementation may raise implementation-defined errors or warnings for function assertions, e.g. if the parameters are not correct for a given assertion. If the namespace URI of a function assertion's expanded QName is not recognized by an implementation, it is ignored, and has no effect on the semantics of the function test.

Note:

An implementation is free to raise warnings for function assertions that it does not recognize.

Note:

Although function assertions use the same syntax as annotations, they are not directly related to annotations. If an implementation defines the annotation blue and uses it in function declarations, there is no guarantee that it will also define a function assertion blue, or that a function assertion named blue matches a function declared with the annotation blue. Of course, an implementation that does so may be more intuitive to users.

Implementations must not define function assertions in reserved namespaces; it is is a static error [err:XQST0045] for a user to define a function assertion in a reserved namespace.

2.5.5.8 Map Test
[210]    MapTest    ::=    AnyMapTest | TypedMapTest
[211]    AnyMapTest    ::=    "map" "(" "*" ")"
[212]    TypedMapTest    ::=    "map" "(" AtomicOrUnionType "," SequenceType ")"

The MapTest map(*) matches any map. The MapTest map(X, Y) matches any map where the type of every key is an instance of X and the type of every value is an instance of Y.

Examples:

Given a map $M whose keys are integers and whose results are strings, such as map{0:"no", 1:"yes"}, consider the results of the following expressions:

  • $M instance of map(*) returns true()

  • $M instance of map(xs:integer, xs:string) returns true()

  • $M instance of map(xs:decimal, xs:anyAtomicType) returns true()

  • not($M instance of map(xs:int, xs:string)) returns true()

  • not($M instance of map(xs:integer, xs:token)) returns true()

Because of the rules for subtyping of function types according to their signature, it follows that the item type function(A) as item()*, where A is an atomic type, also matches any map, regardless of the type of the keys actually found in the map. For example, a map whose keys are all strings can be supplied where the required type is function(xs:integer) as item()*; a call on the map that treats it as a function with an integer argument will always succeed, and will always return an empty sequence.

The function signature of a map matching type map(K, V), treated as a function, is function(xs:anyAtomicType) as V?. It is thus always a subtype of function(xs:anyAtomicType) as item()* regardless of the actual types of the keys and values in the map. The rules for function coercion mean that any map can be supplied as a value in a context where the required type has a more specific return type, such as function(xs:anyAtomicType) as xs:integer, even when the map does not match in the sense required to satisfy the instance of operator. In such cases, a type error will only occur if an actual call on the map (treated as a function) returns a value that is not an instance of the required return type.

Examples:

  • $M instance of function(*) returns true()

  • $M instance of function(xs:anyAtomicType) as item()* returns true()

  • $M instance of function(xs:integer) as item()* returns true()

  • $M instance of function(xs:int) as item()* returns true()

  • $M instance of function(xs:string) as item()* returns true()

  • not($M instance of function(xs:integer) as xs:string) returns true()

Note:

The last case might seem surprising; however, function coercion ensures that $M can be used successfully anywhere that the required type is function(xs:integer) as xs:string.

2.5.5.9 Array Test
[213]    ArrayTest    ::=    AnyArrayTest | TypedArrayTest
[214]    AnyArrayTest    ::=    "array" "(" "*" ")"
[215]    TypedArrayTest    ::=    "array" "(" SequenceType ")"

The AnyArrayTest array(*) matches any array. The TypedArrayTest array(X) matches any array in which every array member matches the SequenceType X.

Examples:

  • [ 1, 2 ] instance array(*) returns true()

  • [] instance of array(xs:string) returns true()

  • [ "foo" ] instance of array(xs:string) returns true()

  • [ "foo" ] instance of array(xs:integer) returns false()

  • [(1,2),(3,4)] instance of array(xs:integer) returns false()

  • [(1,2),(3,4)] instance of array(xs:integer+) returns true()

An array also matches certain other ItemTypes, including:

  • item()

  • function(*)

  • function(xs:integer) as item()*

The function signature of an array matching array(X), treated as a function, is function(xs:integer) as X. It is thus always a subtype of function(xs:integer) as item()* regardless of the actual member types in the array. The rules for function coercion mean that any array can be supplied as a value in a context where the required type has a more specific return type, such as function(xs:integer) as xs:integer, even when the array does not match in the sense required to satisfy the instance of operator. In such cases, a type error will only occur if an actual call on the array (treated as a function) returns a value that is not an instance of the required return type.

2.5.6 SequenceType Subtype Relationships

Given two sequence types, it is possible to determine if one is a subtype of the other. [Definition: A sequence type A is a subtype of a sequence type B if the judgement subtype(A, B) is true.] When the judgement subtype(A, B) is true, it is always the case that for any value V, (V instance of A) implies (V instance of B).

2.5.6.1 The judgement subtype(A, B)

The judgement subtype(A, B) determines if the sequence type A is a subtype of the sequence type B. A can either be empty-sequence(), xs:error, or an ItemType, Ai, possibly followed by an occurrence indicator. Similarly B can either be empty-sequence(), xs:error, or an ItemType, Bi, possibly followed by an occurrence indicator. The result of the subtype(A, B) judgement can be determined from the table below, which makes use of the auxiliary judgement subtype-itemtype(Ai, Bi) defined in 2.5.6.2 The judgement subtype-itemtype(Ai, Bi) .

Sequence type B
empty-sequence() Bi? Bi* Bi Bi+ xs:error
Sequence type A empty-sequence() true true true false false false
Ai? false subtype-itemtype(Ai, Bi) subtype-itemtype(Ai, Bi) false false false
Ai* false false subtype-itemtype(Ai, Bi) false false false
Ai false subtype-itemtype(Ai, Bi) subtype-itemtype(Ai, Bi) subtype-itemtype(Ai, Bi) subtype-itemtype(Ai, Bi) false
Ai+ false false subtype-itemtype(Ai, Bi) false subtype-itemtype(Ai, Bi) false
xs:error true true true true true true

xs:error+ is treated the same way as xs:error in the above table. xs:error? and xs:error* are treated the same way as empty-sequence().

2.5.6.2 The judgement subtype-itemtype(Ai, Bi)

The judgement subtype-itemtype(Ai, Bi) determines if the ItemType Ai is a subtype of the ItemType Bi. Ai is a subtype of Bi if and only if at least one of the following conditions applies:

  1. Ai and Bi are AtomicOrUnionTypes, and derives-from(Ai, Bi) returns true.

  2. Ai is a pure union type, and every type t in the transitive membership of Ai satisfies subtype-itemType(t, Bi).

  3. Ai is xs:error and Bi is a generalized atomic type.

  4. Bi is item().

  5. Bi is node(), and Ai is a KindTest.

  6. Bi is text() and Ai is also text().

  7. Bi is comment() and Ai is also comment().

  8. Bi is namespace-node() and Ai is also namespace-node().

  9. Bi is processing-instruction() and Ai is either processing-instruction() or processing-instruction(N) for any name N.

  10. Bi is processing-instruction(Bn), and Ai is also processing-instruction(Bn).

  11. Bi is document-node() and Ai is either document-node() or document-node(E) for any ElementTest E.

  12. Bi is document-node(Be) and Ai is document-node(Ae), and subtype-itemtype(Ae, Be).

  13. Bi is either element() or element(*), and Ai is an ElementTest.

  14. Bi is either element(Bn) or element(Bn, xs:anyType?), the expanded QName of An equals the expanded QName of Bn, and Ai is either element(An) or element(An, T) or element(An, T?) for any type T.

  15. Bi is element(Bn, Bt), the expanded QName of An equals the expanded QName of Bn, Ai is element(An, At), and derives-from(At, Bt) returns true.

  16. Bi is element(Bn, Bt?), the expanded QName of An equals the expanded QName of Bn, Ai is either element(An, At) or element(An, At?), and derives-from(At, Bt) returns true.

  17. Bi is element(*, Bt), Ai is either element(*, At) or element(N, At) for any name N, and derives-from(At, Bt) returns true.

  18. Bi is element(*, Bt?), Ai is either element(*, At), element(*, At?), element(N, At), or element(N, At?) for any name N, and derives-from(At, Bt) returns true.

  19. Bi is schema-element(Bn), Ai is schema-element(An), and every element declaration that is an actual member of the substitution group of An is also an actual member of the substitution group of Bn.

    Note:

    The fact that P is a member of the substitution group of Q does not mean that every element declaration in the substitution group of P is also in the substitution group of Q. For example, Q might block substitution of elements whose type is derived by extension, while P does not.

  20. Bi is either attribute() or attribute(*), and Ai is an AttributeTest.

  21. Bi is either attribute(Bn) or attribute(Bn, xs:anyType), the expanded QName of An equals the expanded QName of Bn, and Ai is either attribute(An), or attribute(An, T) for any type T.

  22. Bi is attribute(Bn, Bt), the expanded QName of An equals the expanded QName of Bn, Ai is attribute(An, At), and derives-from(At, Bt) returns true.

  23. Bi is attribute(*, Bt), Ai is either attribute(*, At), or attribute(N, At) for any name N, and derives-from(At, Bt) returns true.

  24. Bi is schema-attribute(Bn), the expanded QName of An equals the expanded QName of Bn, and Ai is schema-attribute(An).

  25. Bi is [AnnotationsB] function(*), Ai is a FunctionTest with annotations [AnnotationsA], and subtype-assertions(AnnotationsA, AnnotationsB), where [AnnotationsB] and [AnnotationsA] are optional lists of one or more annotations.

  26. Bi is AnnotationsB function(Ba_1, Ba_2, ... Ba_N) as Br, Ai is AnnotationsA function(Aa_1, Aa_2, ... Aa_M) as Ar, where [AnnotationsB] and [AnnotationsA] are optional lists of one or more annotations; N (arity of Bi) equals M (arity of Ai); subtype(Ar, Br); for values of I between 1 and N, subtype(Ba_I, Aa_I) ; and subtype-assertions(AnnotationsA, AnnotationsB) .

    Note:

    Function return types are covariant because this rule invokes subtype(Ar, Br) for return types. Function arguments are contravariant because this rule invokes subtype(Ba_I, Aa_I) for arguments.

  27. Ai is map(K, V), for any K and V and Bi is map(*).

  28. Ai is map(Ka, Va) and Bi is map(Kb, Vb), where subtype-itemtype(Ka, Kb) and subtype(Va, Vb).

  29. Ai is map(*) (or, because of the transitivity rules, any other map type), and Bi is function(*).

  30. Ai is map(*) (or, because of the transitivity rules, any other map type), and Bi is function(xs:anyAtomicType) as item()*.

  31. Ai is array(X) and Bi is array(*).

  32. Ai is array(X) and Bi is array(Y), and subtype(X, Y) is true.

  33. Ai is array(*) (or, because of the transitivity rules, any other array type) and Bi is function(*).

  34. Ai is array(*) (or, because of the transitivity rules, any other array type) and Bi is function(xs:integer) as item()*.

  35. Ai is map(K, V), and Bi is function(xs:anyAtomicType) as V?.

  36. Ai is array(X) and Bi is function(xs:integer) as X.

2.5.6.3 The judgement subtype-assertions(AnnotationsA, AnnotationsB)

The judgement subtype-assertions(AnnotationsA, AnnotationsB) determines if AnnotationsA is a subtype of AnnotationsB, where AnnotationsA and AnnotationsB are annotation lists from two FunctionTests. It is defined to ignore function assertions in namespaces not understood by the XQuery implementation. For assertions that are understood, their effect on the result of subtype-assertions() is implementation defined.

The following examples are some possible ways to define subtype-assertions() for some implementation defined assertions in the local namespace. These examples assume that some implementation uses annotations to label functions as deterministic or nondeterministic, and treats deterministic functions as a subset of nondeterministic functions. In this implementation, nondeterministic functions are not a subset of deterministic functions.

  • AnnotationsA is

    %local:inline

    It has no influence on the outcome of subtype-assertions().

  • AnnotationsA is

    %local:deterministic

    AnnotationsB is

    %local:nondeterministic

    Since deterministic functions are a subset of nondeterministic functions, subtype-assertions() is true.

  • AnnotationsA contains

    %local:nondeterministic

    AnnotationsB is empty. If FunctionTests without the %local:nondeterministic annotation only match deterministic functions, subtype-assertions() must be false.

2.5.7 xs:error

The type xs:error has an empty value space; it never appears as a dynamic type or as the content type of a dynamic element or attribute type. It was defined in XML Schema in the interests of making the type system complete and closed, and it is also available in XQuery 3.1 for similar reasons.

Note:

Even though it cannot occur in an instance, xs:error is a valid type name in a sequence type. The practical uses of xs:error as a sequence type are limited, but they do exist. For instance, an error handling function that always raises a dynamic error never returns a value, so xs:error is a good choice for the return type of the function.

The semantics of xs:error are well-defined as a consequence of the fact that xs:error is defined as a union type with no member types. For example:

  • $x instance of xs:error always returns false, regardless of the value of $x.

  • $x cast as xs:error fails dynamically with error [err:FORG0001]FO31, regardless of the value of $x.

  • $x cast as xs:error? raises a dynamic error [err:FORG0001]FO31 if exists($x), evaluates to the empty sequence if empty($x).

  • xs:error($x) has the same semantics as $x cast as xs:error? (see the previous bullet point)

  • $x castable as xs:error evaluates to false, regardless of the value of $x.

  • $x treat as xs:error raises a dynamic error [err:XPDY0050] if evaluated, regardless of the value of $x. It never fails statically.

  • let $x as xs:error := 1 return 2 raises a type error [err:XPTY0004], which can be raised statically or dynamically, and need not be raised if the variable $x is never evaluated by the query processor.

  • declare function ns:f($arg as xs:error) {...}; is a valid function declaration, but it always raises a type error [err:XPTY0004] if the function is called.

All of the above examples assume that $x is actually evaluated. If the result of the query does not depend on the value of $x. the rules specified in 2.3.4 Errors and Optimization permit an implementation to avoid evaluating $x and thus to avoid raising an error.

2.6 Comments

[231]    Comment    ::=    "(:" (CommentContents | Comment)* ":)" /* ws: explicit */
/* gn: comments */
[239]    CommentContents    ::=    (Char+ - (Char* ('(:' | ':)') Char*))

Comments may be used to provide information relevant to programmers who read a query, either in the Prolog or in the Query Body . Comments are lexical constructs only, and do not affect query processing.

Comments are strings, delimited by the symbols (: and :). Comments may be nested.

A comment may be used anywhere ignorable whitespace is allowed (see A.2.4.1 Default Whitespace Handling).

The following is an example of a comment:

(: Houston, we have a problem :)

3 Expressions

This section discusses 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 3.1 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 the complete grammar, see Appendix [A XQuery 3.1 Grammar].

[Definition: A query consists of one or more modules.] 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.

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

The XQuery 3.1 operator that has lowest precedence is the comma operator, which is used to combine two operands to form a sequence. As shown in the grammar, a general expression (Expr) can consist of multiple ExprSingle operands, separated by commas. 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, SwitchExpr, TypeswitchExpr, IfExpr, TryCatchExpr, and OrExpr. Each of these expressions is described in a separate section of this document.

3.1 Primary Expressions

[Definition: Primary expressions are the basic primitives of the language. They include literals, variable references, context item expressions, constructors, and function calls. A primary expression may also be created by enclosing any expression in parentheses, which is sometimes helpful in controlling the precedence of operators.] Node Constructors are described in 3.9 Node Constructors. Map and Array Constructors are described in 3.11 Maps and Arrays. String Constructors are described in 3.10 String Constructors.

[128]    PrimaryExpr    ::=    Literal
| VarRef
| ParenthesizedExpr
| ContextItemExpr
| FunctionCall
| OrderedExpr
| UnorderedExpr
| NodeConstructor
| FunctionItemExpr
| MapConstructor
| ArrayConstructor
| StringConstructor
| UnaryLookup
[167]    FunctionItemExpr    ::=    NamedFunctionRef | InlineFunctionExpr

3.1.1 Literals

[Definition: A literal is a direct syntactic representation of an atomic value.] XQuery 3.1 supports two kinds of literals: numeric literals and string literals.

[129]    Literal    ::=    NumericLiteral | StringLiteral
[130]    NumericLiteral    ::=    IntegerLiteral | DecimalLiteral | DoubleLiteral
[219]    IntegerLiteral    ::=    Digits
[220]    DecimalLiteral    ::=    ("." Digits) | (Digits "." [0-9]*) /* ws: explicit */
[221]    DoubleLiteral    ::=    (("." Digits) | (Digits ("." [0-9]*)?)) [eE] [+-]? Digits /* ws: explicit */
[222]    StringLiteral    ::=    ('"' (PredefinedEntityRef | CharRef | EscapeQuot | [^"&])* '"') | ("'" (PredefinedEntityRef | CharRef | EscapeApos | [^'&])* "'") /* ws: explicit */
[225]    PredefinedEntityRef    ::=    "&" ("lt" | "gt" | "amp" | "quot" | "apos") ";" /* ws: explicit */
[226]    EscapeQuot    ::=    '""'
[227]    EscapeApos    ::=    "''"
[238]    Digits    ::=    [0-9]+

The value of a numeric literal containing no "." and no e or E character is an atomic value of type xs:integer. The value of a numeric literal containing "." but no e or E character is an atomic value of type xs:decimal. The value of a numeric literal containing an e or E character is an atomic value of type xs:double. The value of the numeric literal is determined by casting it to the appropriate type according to the rules for casting from xs:untypedAtomic to a numeric type as specified in Section 19.2 Casting from xs:string and xs:untypedAtomic FO31.

Note:

The effect of the above rule is that in the case of an integer or decimal literal, a dynamic error [err:FOAR0002]FO31 will generally be raised if the literal is outside the range of values supported by the implementation (other options are available: see Section 4.2 Arithmetic operators on numeric values FO31 for details.)

The limits of numeric datatypes are specified in 5.3 Data Model Conformance.

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.

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

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

A string literal may also contain a character reference. [Definition: A character reference is an XML-style reference to a [Unicode] character, identified by its decimal or hexadecimal codepoint.] For example, the Euro symbol (€) can be represented by the character reference &#8364;. Character references are normatively defined in Section 4.1 of the XML specification (it is implementation-defined whether the rules in [XML 1.0] or [XML 1.1] apply.) A static error [err:XQST0090] is raised if a character reference does not identify a valid character in the version of XML that is in use.

Here are some examples of literal expressions:

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

  • 12 denotes the xs:integer value twelve.

  • 12.5 denotes the xs:decimal value twelve and one half.

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

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

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

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

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

Values of other simple types can be constructed by calling the constructor function for the given type. The constructor functions for XML Schema built-in types are defined in Section 18.1 Constructor functions for XML Schema built-in atomic types FO31. 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.

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

Constructor functions can also be used to create special values that have no literal representation, as in the following examples:

  • xs:float("NaN") returns the special floating-point value, "Not a Number."

  • xs:double("INF") returns the special double-precision value, "positive infinity."

Constructor functions are available for all simple types, including union types. For example, if my:dt is a user-defined union type whose member types are xs:date, xs:time, and xs:dateTime, then the expression my:dt("2011-01-10") creates an atomic value of type xs:date. The rules follow XML Schema validation rules for union types: the effect is to choose the first member type that accepts the given string in its lexical space.

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

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

3.1.2 Variable References

[131]    VarRef    ::=    "$" VarName
[132]    VarName    ::=    EQName

[Definition: A variable reference is an EQName preceded by a $-sign.] An unprefixed variable reference is in no namespace. Two variable references are equivalent if their expanded QNames are equal (as defined by the eq operator). The scope of a variable binding is defined separately for each kind of expression that can bind variables.

Every variable reference must match a name in the in-scope variables.

Every variable binding has a static scope. The scope defines where references to the variable can validly occur. It is a static error [err:XPST0008] 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 except where it is occluded by another binding that uses the same name within that scope.

A reference to a variable that was declared external, but was not bound to a value by the external environment, raises a dynamic error [err:XPDY0002].

At evaluation time, the value of a variable reference is the value to which the relevant variable is bound.

3.1.3 Parenthesized Expressions

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

Parentheses may be used to override the precedence rules. 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 3.4.1 Constructing Sequences.

3.1.4 Context Item Expression

[134]    ContextItemExpr    ::=    "."

A context item expression evaluates to the context item, which may be either a node (as in the expression fn:doc("bib.xml")/books/book[fn:count(./author)>1]), or an atomic value or function (as in the expression (1 to 100)[. mod 5 eq 0]).

If the context item is absentDM31, a context item expression raises a dynamic error [err:XPDY0002].

3.1.5 Static Function Calls

[Definition: The built-in functions are the functions defined in [XQuery and XPath Functions and Operators 3.1] in the http://www.w3.org/2005/xpath-functions, http://www.w3.org/2001/XMLSchema, http://www.w3.org/2005/xpath-functions/math, http://www.w3.org/2005/xpath-functions/map, and http://www.w3.org/2005/xpath-functions/array namespaces. ] The set of built-in functions is specified in 5.1 Minimal Conformance and 5.2 Optional Features. 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.

[137]    FunctionCall    ::=    EQName ArgumentList /* xgc: reserved-function-names */
/* gn: parens */
[122]    ArgumentList    ::=    "(" (Argument ("," Argument)*)? ")"
[138]    Argument    ::=    ExprSingle | ArgumentPlaceholder
[139]    ArgumentPlaceholder    ::=    "?"

[Definition: A static function call consists of an EQName followed by a parenthesized list of zero or more arguments.] [Definition: An argument to a function call is either an argument expression or an ArgumentPlaceholder ("?").] If the EQName in a static function call is a lexical QName that has no namespace prefix, it is considered to be in the default function namespace.

If the expanded QName and number of arguments in a static function call do not match the name and arity of a function signature in the static context, a static error is raised [err:XPST0017].

[Definition: A static or dynamic function call is a partial function application if one or more arguments is an ArgumentPlaceholder. ]

Evaluation of function calls is described in 3.1.5.1 Evaluating Static and Dynamic Function Calls.

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 static function calls:

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

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

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

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

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

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

3.1.5.1 Evaluating Static and Dynamic Function Calls

When a static or dynamic function call FC is evaluated with respect to a static context SC and a dynamic context DC, the result is obtained as follows:

  1. [Definition: The number of Arguments in an ArgumentList is its arity. ]

  2. The function F to be called or partially applied is obtained as follows:

    1. If FC is a static function call: Using the expanded QName corresponding to FC's EQName, and the arity of FC's ArgumentList, the corresponding function is looked up in the named functions component of DC. Let F denote the function obtained.

    2. If FC is a dynamic function call: FC's base expression is evaluated with respect to SC and DC. If this yields a sequence consisting of a single function with the same arity as the arity of the ArgumentList, let F denote that function. Otherwise, a type error is raised [err:XPTY0004].

  3. [Definition: Argument expressions are evaluated with respect to DC, producing argument values.] 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.

  4. Each argument value is converted to the corresponding parameter type in F's signature by applying the function conversion rules, resulting in a converted argument value.

  5. The remainder depends on whether or not FC is a partial function application.

    1. If FC is a partial function application the result of the function call is a new function, which is a partially applied function. [Definition: A partially applied function is a function created by partial function application.] [Definition: In a partial function application, a fixed position is an argument/parameter position for which the ArgumentList has an argument expression (as opposed to an ArgumentPlaceholder).] A partial function application need not have any fixed positions. A partially applied function has the following properties (which are defined in Section 2.8.1 Functions DM31):

      • name: Absent.

      • parameter names: The parameter names of F, removing the parameter names at the fixed positions. (So the function's arity is the arity of F minus the number of fixed positions.)

      • signature: The signature of F, removing the parameter type at each of the fixed positions. An implementation which can determine a more specific signature (for example, through use of type analysis) is permitted to do so.

      • implementation: The implementation of F. If this is not an XQuery 3.1 expression then the new function's implementation is associated with a static context and a dynamic context in one of two ways: if F's implementation is already associated with contexts, then those are used; otherwise, SC and DC are used.

      • nonlocal variable bindings: The nonlocal variable bindings of F, plus, for each fixed position, a binding of the converted argument value to the corresponding parameter name.

      Example: Partial Application of an Anonymous Function

      In the following example, $f is an anonymous function, and $paf is a partially applied function created from $f.

      let $f := function ($seq, $delim) { fn:fold-left($seq, "", fn:concat(?, $delim, ?)) },
          $paf := $f(?, ".")
      return $paf(1 to 5)
      

      $paf is also an anonymous function. It has one parameter, named $delim, which is taken from the corresponding parameter in $f (the other parameter is fixed). The implementation of $paf is the implementation of $f, which is fn:fold-left($seq, "", fn:concat(?, $delim, ?)). This implementation is associated with the SC and DC of the original expression in $f. The nonlocal bindings associate the value "." with the parameter $delim.

      Example: Partial Application of a Built-In Function

      The following partial function application creates a function that computes the sum of squares of a sequence.

      let $sum-of-squares := fn:fold-right(?, 0, function($a, $b) { $a*$a + $b })
      return $sum-of-squares(1 to 3)

      $sum-of-squares is an anonymous function. It has one parameter, named $seq, which is taken from the corresponding parameter in fn:fold-right (the other two parameters are fixed). The implementation is the implementation of fn:fold-right, which is a built-in context-independent function. The nonlocal bindings contain the fixed bindings for the second and third parameters of fn:fold-right.

      Partial function application never returns a map or an array. If $F is a map or an array, then $F(?) is a partial function application that returns a function, but the function it returns is not a map nor an array.

      Example: Partial Application of a Map

      The following partial function application converts a map to an equivalent function that is not a map.

      let $a := map {"A": 1, "B": 2}(?)
      return $a("A")
    2. If FC is not a partial function application, the semantics of the call depend on the nature of function F's 'implementation' property (see Section 2.8.1 Functions DM31):

      Note:

      XQuery 3.1 is a host language with respect to the data model. In XQuery 3.1, if the implementation is a host language expression, then it is an XQuery 3.1 expression.

      1. If F is a map, it is evaluated as described in 3.11.1.2 Map Lookup using Function Call Syntax. If F is an array, it is evaluated as described in 3.11.2.2 Array Lookup using Function Call Syntax.

      2. If F's implementation is an XQuery 3.1 expression (e.g., F is a user-defined function or an anonymous function, or a partial application of such a function):

        1. F's implementation is evaluated. The static context for this evaluation is the static context of the XQuery 3.1 expression. The dynamic context for this evaluation is obtained by taking the dynamic context of the module that contains the FunctionBody, and making the following changes:

          • The focus (context item, context position, and context size) is absentDM31.

          • In the variable values component of the dynamic context, each converted argument value is bound to the corresponding parameter name.

            When this is done, the converted argument value retains its most specific dynamic type, even though this type may be derived from 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 call, the dynamic type of $p inside the body of the function is considered to be xs:integer.

          • F's nonlocal variable bindings are also added to the variable values. (Note that the names of the nonlocal variables are by definition disjoint from the parameter names, so there can be no conflict.)

        2. The value returned by evaluating the function body is then converted to the declared return type of F by applying the function conversion rules. The result is then the result of evaluating FC.

          As with argument values, the value returned by a function retains its most specific type, which may be derived from the declared return type of F. For example, a function that has a declared return type of xs:decimal may in fact return a value of dynamic type xs:integer.

        Example: Derived Types and Nonlocal Variable Bindings

        $incr is a nonlocal variable that is available within the function because its variable binding has been added to the variable values of the function.. Even though the parameter and return type of this function are both xs:decimal, the more specific type xs:integer is preserved in both cases.

        let $incr := 1,
            $f := function ($i as xs:decimal) as xs:decimal { $i + $incr }
        return $f(5)                      
        Example: Using the Context Item in an Anonymous Function

        The following example will raise a dynamic error [err:XPDY0002]:

        let $vat := function() { @vat + @price }
        return shop/article/$vat()

        Instead, the context item can be used as an argument to the anonymous function:

        let $vat := function($art) { $art/@vat + $art/@price }
        return shop/article/$vat(.)

        Or, the value can be referenced as a nonlocal variable binding:

        let $ctx := shop/article,
        $vat := function() { for $a in $ctx return $a/@vat + $a/@price }
        return $vat()
        
      3. If F's implementation is not an XQuery 3.1 expression (e.g., F is a built-in function or an external function or a partial application of such a function):

        • F's implementation is invoked in an implementation-dependent way. The processor makes the following information available to that invocation:

          • the converted argument values;

          • F's nonlocal variable bindings; and

          • a static context and dynamic context. If F's implementation is associated with a static and a dynamic context, then these are supplied, otherwise SC and DC are supplied.

          How this information is used is implementation-defined. An API used to invoke external functions must state how the static and dynamic contexts are provided to a function that is invoked. The F&O specification states how the static and dynamic contexts are used in each function that it defines.

        • The result is either an instance of F's return type or a dynamic error. This result is then the result of evaluating FC.

        • Errors raised by built-in functions are defined in [XQuery and XPath Functions and Operators 3.1].

        • Errors raised by external functions are implementation-defined (see 2.2.5 Consistency Constraints).

        Example: A Built-in Function

        The following function call uses the function Section 2.5 fn:base-uri FO31. Use of SC and DC and errors raised by this function are all defined in [XQuery and XPath Functions and Operators 3.1].

        fn:base-uri()
3.1.5.2 Function Conversion Rules

[Definition: 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 parameter or return. ] The expected type is expressed as a sequence type. The function conversion rules are applied to a given value as follows:

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

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

    2. Each item in the atomic sequence that is of type xs:untypedAtomic is cast to the expected generalized atomic type. If the item is of type xs:untypedAtomic and the expected type is namespace-sensitive, a type error [err:XPTY0117] is raised.

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

    4. For each item of type xs:anyURI in the atomic sequence that can be promoted to the expected atomic type using URI promotion as described in B.1 Type Promotion, the promotion is done.

  • If the expected type is a TypedFunctionTest (possibly with an occurrence indicator *, +, or ?), function coercion is applied to each function in the given value.

    Note:

    In XQuery 3.1, maps and arrays are functions, so function coercion applies to them as well.

  • 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:XPTY0004]. If the function call takes place in a module other than the module in which the function is defined, this rule must be satisfied in both the module where the function is called and the module where the function is defined (the test is repeated because the two modules may have different in-scope schema definitions.) Note that the rules for SequenceType Matching permit a value of a derived type to be substituted for a value of its base type.

3.1.5.3 Function Coercion

Function coercion is a transformation applied to functionsDM31 during application of the function conversion rules. [Definition: Function coercion wraps a functionDM31 in a new function with signature the same as the expected type. This effectively delays the checking of the argument and return types until the function is invoked.]

Function coercion is only defined to operate on functionsDM31. Given a function F, and an expected function type, function coercion proceeds as follows: If F and the expected type have different arity, a type error is raised [err:XPTY0004]. Otherwise, coercion returns a new function with the following properties (as defined in Section 2.8.1 Functions DM31):

  • name: The name of F.

  • parameter names: The parameter names of F.

  • signature: Annotations is set to the annotations of F. TypedFunctionTest is set to the expected type.

  • implementation: In effect, a FunctionBody that calls F, passing it the parameters of this new function, in order.

  • nonlocal variable bindings: An empty mapping.

If the result of invoking the new function would necessarily result in a type error, that error may be raised during function coercion. It is implementation dependent whether this happens or not.

These rules have the following consequences:

  • SequenceType matching of the function's arguments and result are delayed until that function is invoked.

  • The function conversion rules applied to the function's arguments and result are defined by the SequenceType it has most recently been coerced to. Additional function conversion rules could apply when the wrapped function is invoked.

  • If an implementation has static type information about a function, that can be used to type check the function's argument and return types during static analysis.

For instance, consider the following query:

declare function local:filter($s as item()*, $p as function(xs:string) as xs:boolean) as item()*
{
  $s[$p(.)]
};

let $f := function($a) { starts-with($a, "E") }
return
  local:filter(("Ethel", "Enid", "Gertrude"), $f)
      

The function $f has a static type of function(item()*) as item()*. When the local:filter() function is called, the following occurs to the function:

  1. The function conversion rules result in applying function coercion to $f, wrapping $f in a new function ($p) with the signature function(xs:string) as xs:boolean.

  2. $p is matched against the SequenceType of function(xs:string) as xs:boolean, and succeeds.

  3. When $p is invoked inside the predicate, function conversion and SequenceType matching rules are applied to the context item argument, resulting in an xs:string value or a type error.

  4. $f is invoked with the xs:string, which returns an xs:boolean.

  5. $p applies function conversion rules to the result sequence from $f, which already matches its declared return type of xs:boolean.

  6. The xs:boolean is returned as the result of $p.

Note:

Although the semantics of function coercion are specified in terms of wrapping the functions, static typing will often be able to reduce the number of places where this is actually necessary.

Since maps and arrays are also functions in XQuery 3.1, function coercion applies to them as well. For instance, consider the following expression:

let $m := map {
  "Monday" : true(),
  "Wednesday" : true(),
  "Friday" : true(),
  "Saturday" : false(),
  "Sunday" : false()
},
$days := ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
return fn:filter($days,$m)
      

The map $m has a function signature of function(xs:anyAtomicType) as item()*. When the fn:filter() function is called, the following occurs to the map:

  1. The map $m is treated as function ($f), equivalent to map:get($m,?).

  2. The function conversion rules result in applying function coercion to $f, wrapping $f in a new function ($p) with the signature function(item()) as xs:boolean.

  3. $p is matched against the SequenceType function(item()) as xs:boolean, and succeeds.

  4. When $p is invoked by fn:filter(), function conversion and SequenceType matching rules are applied to the argument, resulting in an item() value ($a) or a type error.

  5. $f is invoked with $a, which returns an xs:boolean or the empty sequence.

  6. $p applies function conversion rules and SequenceType matching to the result sequence from $f. When the result is an xs:boolean the SequenceType matching succeeds. When it is an empty sequence (such as when $m does not contain a key for "Tuesday"), SequenceType matching results in a type error [err:XPTY0004], since the expected type is xs:boolean and the actual type is an empty sequence.

Consider the following expression:

let $m := map {
"Monday" : true(),
"Tuesday" : false(),
"Wednesday" : true(),
"Thursday" : false(),
"Friday" : true(),
"Saturday" : false(),
"Sunday" : false()
}
let $days := ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
return fn:filter($days,$m)
      

The result of the expression is the sequence ("Monday", "Wednesday", "Friday")

3.1.6 Named Function References

[168]    NamedFunctionRef    ::=    EQName "#" IntegerLiteral /* xgc: reserved-function-names */
[218]    EQName    ::=    QName | URIQualifiedName

[Definition: A named function reference is an expression which evaluates to a named function. The name and arity of the returned function are known statically, and correspond to a function signature present in the static context; if the function is context dependent, then the returned function is associated with the static context of the named function reference and the dynamic context in which it is evaluated. ] [Definition: A named function is a function defined in the static context for the query. To uniquely identify a particular named function, both its name as an expanded QName and its arity are required.]

If the EQName is a lexical QName that has no namespace prefix, it is considered to be in the default function namespace.

If the expanded QName and arity in a named function reference do not match the name and arity of a function signature in the static context, a static error is raised [err:XPST0017].

The value of a NamedFunctionRef is the function obtained by looking up the expanded QName and arity in the named functions component of the dynamic context.

Furthermore, if the function returned by the evaluation of a NamedFunctionRef has an implementation-dependent implementation, then the implementation of this function is associated with the static context of this NamedFunctionRef expression and with the dynamic context in which the NamedFunctionRef is evaluated.

The following are examples of named function references:

  • fn:abs#1 references the fn:abs function which takes a single argument.

  • fn:concat#5 references the fn:concat function which takes 5 arguments.

  • local:myfunc#2 references a function named local:myfunc which takes 2 arguments.

3.1.7 Inline Function Expressions

[169]    InlineFunctionExpr    ::=    Annotation* "function" "(" ParamList? ")" ("as" SequenceType)? FunctionBody

[Definition: An inline function expression creates an anonymous function defined directly in the inline function expression.] An inline function expression specifies the names and SequenceTypes of the parameters to the function, the SequenceType of the result, and the body of the function. [Definition: An anonymous function is a function with no name. Anonymous functions may be created, for example, by evaluating an inline function expression or by partial function application.]

If a function parameter is declared using a name but no type, its default type is item()*. If the result type is omitted from an inline function expression, its default result type is item()*.

The parameters of an inline function expression are considered to be variables whose scope is the function body. It is a static error [err:XQST0039] for an inline function expression to have more than one parameter with the same name.

An inline function expression may have annotations. XQuery 3.1 does not define annotations that apply to inline function expressions, in particular it is a static error [err:XQST0125] if an inline function expression is annotated as %public or %private. An implementation can define annotations, in its own namespace, to support functionality beyond the scope of this specification.

The static context for the function body is inherited from the location of the inline function expression, with the exception of the static type of the context item which is initially absentDM31.

The variables in scope for the function body include all variables representing the function parameters, as well as all variables that are in scope for the inline function expression.

Note:

Function parameter names can mask variables that would otherwise be in scope for the function body.

The result of an inline function expression is a single function with the following properties (as defined in Section 2.8.1 Functions DM31):

  • name: An absent name. Absent.

  • parameter names: The parameter names in the InlineFunctionExpr's ParamList.

  • signature: A FunctionTest constructed from the Annotations and SequenceTypes in the InlineFunctionExpr. An implementation which can determine a more specific signature (for example, through use of type analysis of the function's body) is permitted to do so.

  • implementation: The InlineFunctionExpr's FunctionBody.

  • nonlocal variable bindings: For each nonlocal variable, a binding of it to its value in the variable values component of the dynamic context of the InlineFunctionExpr.

The following are examples of some inline function expressions:

  • This example creates a function that takes no arguments and returns a sequence of the first 6 primes:

    function() as xs:integer+ { 2, 3, 5, 7, 11, 13 }
  • This example creates a function that takes two xs:double arguments and returns their product:

    function($a as xs:double, $b as xs:double) as xs:double { $a * $b }
  • This example creates a function that returns its item()* argument:

    function($a) { $a }
  • This example creates a sequence of functions each of which returns a different item from the default collection.

    collection()/(let $a := . return function() { $a })

3.1.8 Enclosed Expressions

[36]    EnclosedExpr    ::=    "{" Expr? "}"

[Definition: An enclosed expression is an instance of the EnclosedExpr production, which allows an optional expression within curly braces.] [Definition: In an enclosed expression, the optional expression enclosed in curly braces is called the content expression.] If the content expression is not provided explicitly, the content expression is ().

3.2 Postfix Expressions

[121]    PostfixExpr    ::=    PrimaryExpr (Predicate | ArgumentList | Lookup)*
[124]    Predicate    ::=    "[" Expr "]"
[122]    ArgumentList    ::=    "(" (Argument ("," Argument)*)? ")"

[Definition: An expression followed by a predicate (that is, E1[E2]) is referred to as a filter expression: its effect is to return those items from the value of E1 that satisfy the predicate in E2.] Filter expressions are described in 3.2.1 Filter Expressions

An expression (other than a raw EQName) followed by an argument list in parentheses (that is, E1(E2, E3, ...)) is referred to as a dynamic function call. Its effect is to evaluate E1 to obtain a function, and then call that function, with E2, E3, ... as arguments. Dynamic function calls are described in 3.2.2 Dynamic Function Calls.

3.2.1 Filter Expressions

[121]    PostfixExpr    ::=    PrimaryExpr (Predicate | ArgumentList | Lookup)*
[124]    Predicate    ::=    "[" Expr "]"

A filter expression consists of a base expression followed by a predicate, which is an expression written in square brackets. The result of the filter expression consists of the items returned by the base expression, filtered by applying the predicate to each item in turn. The ordering of the items returned by a filter expression is the same as their order in the result of the primary expression.

Note:

Where the expression before the square brackets is a ReverseStep or ForwardStep, the expression is technically not a filter expression but an AxisStep. There are minor differences in the semantics: see 3.3.3 Predicates within Steps

Here are some examples of filter expressions:

  • Given a sequence of products in a variable, return only those products whose price is greater than 100.

    $products[price gt 100]
  • List all the integers from 1 to 100 that are divisible by 5. (See 3.4.1 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 25:

    (21 to 29)[5]
  • The following example returns the fifth through ninth items in the sequence bound to variable $orders.

    $orders[fn:position() = (5 to 9)]
  • The following example illustrates the use of a filter expression as a step in a path expression. It returns the last chapter or appendix within the book bound to variable $book:

    $book/(chapter | appendix)[fn:last()]

For each item in the input sequence, the predicate expression is evaluated using an inner focus, defined as follows: The context item is the item currently being tested against the predicate. The context size is the number of items in the input sequence. The context position is the position of the context item within the input sequence.

For each item in the input sequence, the result of the predicate expression is coerced to an xs:boolean value, called the predicate truth value, as described below. Those items for which the predicate truth value is true are retained, and those for which the predicate truth value is false are discarded.

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

  1. If the value of the predicate expression is a singleton atomic value of a numeric type or derived from a numeric type, the predicate truth value is true if the value of the predicate expression is equal (by the eq operator) to the context position, and is false otherwise. [Definition: A predicate whose predicate expression returns a numeric type is called a numeric predicate.]

    Note:

    In a region of a query where ordering mode is unordered, the result of a numeric predicate is implementation-dependent , as explained in 3.13 Ordered and Unordered Expressions.

  2. Otherwise, the predicate truth value is the effective boolean value of the predicate expression.

3.2.2 Dynamic Function Calls

[121]    PostfixExpr    ::=    PrimaryExpr (Predicate | ArgumentList | Lookup)*
[122]    ArgumentList    ::=    "(" (Argument ("," Argument)*)? ")"
[138]    Argument    ::=    ExprSingle | ArgumentPlaceholder
[139]    ArgumentPlaceholder    ::=    "?"

[Definition: A dynamic function call consists of a base expression that returns the function and a parenthesized list of zero or more arguments (argument expressions or ArgumentPlaceholders).]

A dynamic function call is evaluated as described in 3.1.5.1 Evaluating Static and Dynamic Function Calls.

The following are examples of some dynamic function calls:

  • This example invokes the function contained in $f, passing the arguments 2 and 3:

    $f(2, 3)
  • This example fetches the second item from sequence $f, treats it as a function and invokes it, passing an xs:string argument:

    $f[2]("Hi there")
  • This example invokes the function $f passing no arguments, and filters the result with a positional predicate:

    $f()[2]

3.3 Path Expressions

[108]    PathExpr    ::=    ("/" RelativePathExpr?)
| ("//" RelativePathExpr)
| RelativePathExpr
/* xgc: leading-lone-slash */
[109]    RelativePathExpr    ::=    StepExpr (("/" | "//") StepExpr)*

[Definition: A path expression can be used to locate nodes within trees. 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 3.3.2 Steps.

A "/" at the beginning of a path expression is an abbreviation for the initial step (fn:root(self::node()) treat as document-node())/ (however, if the "/" is the entire path expression, the trailing "/" is omitted from the expansion.) 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:XPTY0020]. At evaluation time, if the root node of the context node is not a document node, a dynamic error is raised [err:XPDY0050].

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()/ (however, "//" by itself is not a valid path expression [err:XPST0003].) The effect of these initial steps is to establish an initial node sequence that contains the root of the tree in which the context node is found, plus all nodes descended from this root. This node sequence is used as the input to subsequent steps in the path expression. If the context item is not a node, a type error is raised [err:XPTY0020]. At evaluation time, if the root node of the context node is not a document node, a dynamic error is raised [err:XPDY0050].

Note:

The descendants of a node do not include attribute nodes.

A path expression that starts with "/" or "//" selects nodes starting from the root of the tree containing the context item; it is often referred to as an absolute path expression.

3.3.1 Relative Path Expressions

[109]    RelativePathExpr    ::=    StepExpr (("/" | "//") StepExpr)*

A relative path expression is a path expression that selects nodes within a tree by following a series of steps starting at the context node (which, unlike an absolute path expression, may be any node in a tree).

Each non-initial occurrence of "//" in a path expression is expanded as described in 3.3.5 Abbreviated Syntax, leaving a sequence of steps separated by "/". This sequence of steps is then evaluated from left to right. So a path such as E1/E2/E3/E4 is evaluated as ((E1/E2)/E3)/E4. The semantics of a path expression are thus defined by the semantics of the binary "/" operator, which is defined in 3.3.1.1 Path operator (/).

Note:

Although the semantics describe the evaluation of a path with more than two steps as proceeding from left to right, the "/" operator is in most cases associative, so evaluation from right to left usually delivers the same result. The cases where "/" is not associative arise when the functions fn:position() and fn:last() are used: A/B/position() delivers a sequence of integers from 1 to the size of (A/B), whereas A/(B/position()) restarts the counting at each B element.

The following example illustrates the use of relative path expressions.

  • child::div1/child::para

    Selects the para element children of the div1 element children of the context node; that is, the para element grandchildren of the context node that have div1 parents.

Note:

Since each step in a path provides context nodes for the following step, in effect, only the last step in a path is allowed to return a sequence of non-nodes.

Note:

The "/" character can be used either as a complete path expression or as the beginning of a longer path expression such as "/*". Also, "*" is both the multiply operator and a wildcard in path expressions. This can cause parsing difficulties when "/" appears on the left-hand side of "*". This is resolved using the leading-lone-slash constraint. For example, "/*" and "/ *" are valid path expressions containing wildcards, but "/*5" and "/ * 5" raise syntax errors. Parentheses must be used when "/" is used on the left-hand side of an operator, as in "(/) * 5". Similarly, "4 + / * 5" raises a syntax error, but "4 + (/) * 5" is a valid expression. The expression "4 + /" is also valid, because / does not occur on the left-hand side of the operator.

Similarly, in the expression / union /*, "union" is interpreted as an element name rather than an operator. For it to be parsed as an operator, the expression should be written (/) union /*.

3.3.1.1 Path operator (/)

The path operator "/" is used to build expressions for locating nodes within trees. Its left-hand side expression must return a sequence of nodes. The operator returns either a sequence of nodes, in which case it additionally performs document ordering and duplicate elimination, or a sequence of non-nodes.

Each operation E1/E2 is evaluated as follows: Expression E1 is evaluated, and if the result is not a (possibly empty) sequence S of nodes, a type error is raised [err:XPTY0019]. Each node in S then serves in turn to provide an inner focus (the node as the context item, its position in S as the context position, the length of S as the context size) for an evaluation of E2, as described in 2.1.2 Dynamic Context. The sequences resulting from all the evaluations of E2 are combined as follows:

  1. If every evaluation of E2 returns a (possibly empty) sequence of nodes, these sequences are combined, and duplicate nodes are eliminated based on node identity. If ordering mode is ordered, the resulting node sequence is returned in document order; otherwise it is returned in implementation-dependent order.

  2. If every evaluation of E2 returns a (possibly empty) sequence of non-nodes, these sequences are concatenated and returned. If ordering mode is ordered, the returned sequence preserves the orderings within and among the subsequences generated by the evaluations of E2 ; otherwise the order of the returned sequence is implementation-dependent.

  3. If the multiple evaluations of E2 return at least one node and at least one non-node, a type error is raised [err:XPTY0018].

Note:

The semantics of the path operator can also be defined using the simple map operator as follows (forming the union with an empty sequence ($R | ()) has the effect of eliminating duplicates and sorting nodes into document order):

E1/E2 ::= let $R := E1!E2
  return
    if (every $r in $R satisfies $r instance of node())
    then ($R|())
    else if (every $r in $R satisfies not($r instance of node()))
    then $R
    else error()

3.3.2 Steps

[110]    StepExpr    ::=    PostfixExpr | AxisStep
[111]    AxisStep    ::=    (ReverseStep | ForwardStep) PredicateList
[112]    ForwardStep    ::=    (ForwardAxis NodeTest) | AbbrevForwardStep
[115]    ReverseStep    ::=    (ReverseAxis NodeTest) | AbbrevReverseStep
[123]    PredicateList    ::=    Predicate*

[Definition: A step is a part of a path expression that 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, working from left to right. A step may be either an axis step or a postfix expression.] Postfix expressions are described in 3.2 Postfix Expressions.

[Definition: An axis step returns a sequence of 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 annotation.] If the context item is a node, an axis step returns a sequence of zero or more nodes; otherwise, a type error is raised [err:XPTY0020]. If ordering mode is ordered, the resulting node sequence is returned in document order; otherwise it is returned in implementation-dependent order. An axis step may be either a forward step or a reverse step, followed by zero or more predicates.

In the abbreviated syntax for a step, the axis can be omitted and other shorthand notations can be used as described in 3.3.5 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 annotation 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 3.3.2.1 Axes. The available node tests are described in 3.3.2.2 Node Tests. Examples of steps are provided in 3.3.4 Unabbreviated Syntax and 3.3.5 Abbreviated Syntax.

3.3.2.1 Axes
[113]    ForwardAxis    ::=    ("child" "::")
| ("descendant" "::")
| ("attribute" "::")
| ("self" "::")
| ("descendant-or-self" "::")
| ("following-sibling" "::")
| ("following" "::")
[116]    ReverseAxis    ::=    ("parent" "::")
| ("ancestor" "::")
| ("preceding-sibling" "::")
| ("preceding" "::")
| ("ancestor-or-self" "::")

XQuery supports the following axes:

  • The child axis contains the children of the context node, which are the nodes returned by the Section 5.3 children Accessor DM31.

    Note:

    Only document nodes and element nodes have children. If the context node is any other kind of node, or if the context node is an empty document or element node, then the child axis is an empty sequence. The children of a document node or element node may be element, processing instruction, comment, or text nodes. Attribute and document nodes can never appear as children.

  • the descendant axis is defined as the transitive closure of the child axis; it contains the descendants of the context node (the children, the children of the children, and so on)

  • the parent axis contains the sequence returned by the Section 5.11 parent Accessor DM31, which returns the parent of the context node, or an empty sequence if the context node has no parent

    Note:

    An attribute node may have an element node as its parent, even though the attribute node is not a child of the element node.

  • the ancestor axis is defined as the transitive closure of the parent axis; it contains the ancestors of the context node (the parent, the parent of the parent, and so on)

    Note:

    The ancestor axis includes the root node of the tree in which the context node is found, unless the context node is the root node.

  • the following-sibling axis contains the context node's following siblings, those children of the context node's parent that occur after the context node in document order; if the context node is an attribute node, the following-sibling axis is empty

  • the preceding-sibling axis contains the context node's preceding siblings, those children of the context node's parent that occur before the context node in document order; if the context node is an attribute node, the preceding-sibling axis is empty

  • the following axis contains all nodes that are descendants of the root of the tree in which the context node is found, are not descendants of the context node, and occur after the context node in document order

  • the preceding axis contains all nodes that are descendants of the root of the tree in which the context node is found, are not ancestors of the context node, and occur before the context node in document order

  • the attribute axis contains the attributes of the context node, which are the nodes returned by the Section 5.11 parent Accessor DM31; 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 nodes): they do not overlap and together they contain all the nodes in the document.

[Definition: 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.

3.3.2.2 Node Tests

[Definition: A node test is a condition on the name, kind (element, attribute, text, document, comment, or processing instruction), and/or type annotation of a node. A node test determines which nodes contained by an axis are selected by a step.]

[118]    NodeTest    ::=    KindTest | NameTest
[119]    NameTest    ::=    EQName | Wildcard
[120]    Wildcard    ::=    "*"
| (NCName ":*")
| ("*:" NCName)
| (BracedURILiteral "*")
/* ws: explicit */
[218]    EQName    ::=    QName | URIQualifiedName

[Definition: A node test that consists only of an EQName or a Wildcard is called a name test.] A name test that consists of an EQName is true if and only if the kind of the node is the principal node kind for the step axis and the expanded QName of the node is equal (as defined by the eq operator) 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.

If the EQName is a lexical QName, it is resolved into an expanded QName using the statically known namespaces in the expression context. It is a static error [err:XPST0081] if the QName has a prefix that does not correspond to any statically known namespace. An unprefixed QName, when used as a name test on an axis whose principal node kind is element, has the namespace URI of the default element/type namespace in the expression context; otherwise, it has no namespace URI.

A name test is not satisfied by an element node whose name does not match the expanded 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 of the step axis. 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 lexical QName, using the statically known namespaces in the static context. If the prefix is not found in the statically known namespaces, a static error is raised [err:XPST0081]. The node test is true for any node of the principal node kind of the step axis 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 contain a BracedURILiteral, e.g. Q{http://example.com/msg}* Such a node test is true for any node of the principal node kind of the step axis whose expanded QName has the namespace URI specified in the BracedURILiteral, 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 of the step axis whose local name matches the given NCName, regardless of its namespace or lack of a namespace.

[Definition: An alternative form of a node test called a kind test can select nodes based on their kind, name, and type annotation.] The syntax and semantics of a kind test are described in 2.5.4 SequenceType Syntax and 2.5.5 SequenceType Matching. When a kind test is used in a node test, only those nodes on the designated axis that match the kind test are selected. Shown below are several examples of kind tests that might be used in path expressions:

  • node() matches any node.

  • text() matches any text node.

  • comment() matches any comment node.

  • namespace-node() matches any namespace node.

  • element() matches any element node.

  • schema-element(person) matches any element node whose name is person (or is in the substitution group headed by person), and whose type annotation is the same as (or is derived from) the declared type of the person element in the in-scope element declarations.

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

  • element(person, surgeon) matches any non-nilled element node whose name is person, and whose type annotation is surgeon or is derived from surgeon.

  • element(*, surgeon) matches any non-nilled element node whose type annotation is surgeon (or is derived from surgeon), regardless of its name.

  • 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 (or is derived from 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 kind test element(book), interleaved with zero or more comments and processing instructions.

3.3.3 Predicates within Steps

[111]    AxisStep    ::=    (ReverseStep | ForwardStep) PredicateList
[123]    PredicateList    ::=    Predicate*
[124]    Predicate    ::=    "[" Expr "]"

A predicate within a Step has similar syntax and semantics to a predicate within a filter expression. The only difference is in the way the context position is set for evaluation of the predicate.

For the purpose of evaluating the context position within a predicate, the input sequence is considered to be sorted as follows: into document order if the predicate is in a forward-axis step, into reverse document order if the predicate is in a reverse-axis step, or in its original order if the predicate is not in a step.

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 that are elements named "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 both a secretary child element and an assistant child element:

    child::employee[secretary][assistant]

Note:

When using predicates with a sequence of nodes selected using a reverse axis, it is important to remember that the context positions for such a sequence are assigned in reverse document order. For example, preceding::foo[1] returns the first qualifying foo element in reverse document order, because the predicate is part of an axis step using a reverse axis. By contrast, (preceding::foo)[1] returns the first qualifying foo element in document order, because the parentheses cause (preceding::foo) to be parsed as a primary expression in which context positions are assigned in document order. Similarly, ancestor::*[1] returns the nearest ancestor element, because the ancestor axis is a reverse axis, whereas (ancestor::*)[1] returns the root element (first ancestor in document order).

The fact that a reverse-axis step assigns context positions in reverse document order for the purpose of evaluating predicates does not alter the fact that the final result of the step (when in ordered mode) is always in document order.

3.3.4 Unabbreviated Syntax

This section provides a number of examples of path expressions in which the axis is explicitly specified in each step. The syntax used in these examples is called the unabbreviated syntax. In many common cases, it is possible to write path expressions more concisely using an abbreviated syntax, as explained in 3.3.5 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. Note that no attribute nodes are returned, because attributes are not children.

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

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

  • parent::node() 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 returns an empty sequence

  • 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 tree that contains the context node, but raises a dynamic error if this root is not a document 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 containing the context node

  • /child::book/child::chapter[fn:position() = 5]/child::section[fn:position() = 2] selects the second section of the fifth chapter of the book whose parent is the document node that contains the context node

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

  • child::para[attribute::type eq '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 eq "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 whose typed value is equal to the string Introduction

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

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

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

3.3.5 Abbreviated Syntax

[114]    AbbrevForwardStep    ::=    "@"? NodeTest
[117]    AbbrevReverseStep    ::=    ".."

The abbreviated syntax permits the following abbreviations:

  1. The attribute axis 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.

  2. If the axis name is omitted from an axis step, the default axis is child, with two exceptions: (1) if the NodeTest in an axis step contains an AttributeTest or SchemaAttributeTest then the default axis is attribute; (2) if the NodeTest in an axis step is a NamespaceNodeTest then a static error is raised [err:XQST0134].

    Note:

    The namespace axis is deprecated as of XPath 2.0, but required in some languages that use XPath, including XSLT.

    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.

  3. Each non-initial occurrence of // is effectively replaced by /descendant-or-self::node()/ during processing of a path expression. For example, div1//para is short for child::div1/descendant-or-self::node()/child::para and so will select all para descendants of div1 children.

    Note:

    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 respective parents.

  4. 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

  • /book/chapter[5]/section[2] selects the second section of the fifth chapter of the book whose parent is the document node that contains the context node

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

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

  • //@version selects all the version attribute nodes that are 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 whose typed value is equal to the string 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.

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

3.4 Sequence Expressions

XQuery 3.1 supports operators to construct, filter, 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).

3.4.1 Constructing Sequences

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

[Definition: One way to construct a sequence is by using the comma operator, which evaluates each of its operands and concatenates the resulting sequences, in order, into a single result sequence.] Empty parentheses can be used to denote an empty sequence.

A sequence may contain duplicate items, 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.

Note:

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.

Here are some examples of expressions that construct sequences:

  • The result of this expression is a sequence of five integers:

    (10, 1, 2, 3, 4)
  • This expression combines four sequences of length one, two, zero, and two, respectively, into a single sequence of length five. The result of this expression is the sequence 10, 1, 2, 3, 4.

    (10, (1, 2), (), (3, 4))
  • The result of this expression is a sequence containing all salary children of the context node followed by all bonus children.

    (salary, bonus)
  • Assuming that $price is bound to the value 10.50, the result of this expression is the sequence 10.50, 10.50.

    ($price, $price)

A range expression 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?. If either operand is an empty sequence, or if the integer derived from the first operand is greater than the integer derived from the second operand, the result of the range expression is an empty sequence. If the two operands convert to the same integer, the result of the range expression is that integer. Otherwise, the result is a sequence containing the two integer operands and every integer between the two operands, in increasing order.

  • This example uses a range expression as one operand in constructing a sequence. It evaluates to the sequence 10, 1, 2, 3, 4.

    (10, 1 to 4)
  • This example constructs a sequence of length one containing the single integer 10.

    10 to 10
  • The result of this example is a sequence of length zero.

    15 to 10
  • This example uses the fn:reverse function to construct a sequence of six integers in decreasing order. It evaluates to the sequence 15, 14, 13, 12, 11, 10.

    fn:reverse(10 to 15)

3.4.2 Combining Node Sequences

[90]    UnionExpr    ::=    IntersectExceptExpr ( ("union" | "|") IntersectExceptExpr )*
[91]    IntersectExceptExpr    ::=    InstanceofExpr ( ("intersect" | "except") InstanceofExpr )*

XQuery 3.1 provides the following 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 these operators eliminate duplicate nodes from their result sequences based on node identity. If ordering mode is ordered, the resulting sequence is returned in document order; otherwise it is returned in implementation-dependent order.

If an operand of union, intersect, or except contains an item that is not a node, a type error is raised [err:XPTY0004].

If an IntersectExceptExpr contains more than two InstanceofExprs, they are grouped from left to right. With a UnionExpr, it makes no difference how operands are grouped, the results are the same.

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 ordering mode is ordered. Assume that the variables $seq1, $seq2 and $seq3 are bound to the following sequences of these nodes:

  • $seq1 is bound to (A, B)

  • $seq2 is bound to (A, B)

  • $seq3 is bound to (B, C)

Then:

  • $seq1 union $seq2 evaluates to the sequence (A, B).

  • $seq2 union $seq3 evaluates to the sequence (A, B, C).

  • $seq1 intersect $seq2 evaluates to the sequence (A, B).

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

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

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

In addition to the sequence operators described here, see Section 14 Functions and operators on sequences FO31 for functions defined on sequences.

3.5 Arithmetic Expressions

XQuery 3.1 provides arithmetic operators for addition, subtraction, multiplication, division, and modulus, in their usual binary and unary forms.

[88]    AdditiveExpr    ::=    MultiplicativeExpr ( ("+" | "-") MultiplicativeExpr )*
[89]    MultiplicativeExpr    ::=    UnionExpr ( ("*" | "div" | "idiv" | "mod") UnionExpr )*
[97]    UnaryExpr    ::=    ("-" | "+")* ValueExpr
[98]    ValueExpr    ::=    ValidateExpr | ExtensionExpr | SimpleMapExpr

A 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 and a -b will be interpreted as arithmetic expressions. (See A.2.4 Whitespace Rules for further details on whitespace handling.)

If an AdditiveExpr contains more than two MultiplicativeExprs, they are grouped from left to right. So, for instance,

A - B + C - D

is equivalent to

((A - B) + C) - D

Similarly, the operands of a MultiplicativeExpr are grouped from left to right.

The first step in evaluating an arithmetic expression is to evaluate its operands. The order in which the operands are evaluated is implementation-dependent.

Each operand is evaluated by applying the following steps, in order:

  1. Atomization is applied to the operand. The result of this operation is called the atomized operand.

  2. If the atomized operand is an empty sequence, the result of the arithmetic expression is an empty sequence, and the implementation need not evaluate the other operand or apply the operator. However, an implementation may choose to evaluate the other operand in order to determine whether it raises an error.

  3. If the atomized operand is a sequence of length greater than one, a type error is raised [err:XPTY0004].

  4. If the atomized operand is of type xs:untypedAtomic, it is cast to xs:double. If the cast fails, a dynamic error is raised. [err:FORG0001]FO31

After evaluation of the operands, if the types of the operands are a valid combination for the given arithmetic 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 operator functions that define the semantics of the operator for each type combination, including the dynamic errors that can be raised by the operator. The definitions of the operator functions are found in [XQuery and XPath Functions and Operators 3.1].

If the types of the operands, after evaluation, are not a valid combination for the given operator, according to the rules in B.2 Operator Mapping, a type error is raised [err:XPTY0004].

XQuery 3.1 supports two division operators named div and idiv. Each of these operators accepts two operands of any numeric type. The semantics of div are defined in Section 4.2.5 op:numeric-integer-divide FO31. The semantics of idiv are defined in Section 4.2.4 op:numeric-divide FO31.

Here are some examples of arithmetic expressions:

  • The first expression below returns the xs:decimal value -1.5, and the second expression returns the xs:integer value -1:

    -3 div 2
    -3 idiv 2
  • Subtraction of two date values results in a value of type xs: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 (other than "!", "/", and "[]"), subject of course to the use of parentheses. Therefore, the following two examples have different meanings:

    -$bellcost + $whistlecost
    -($bellcost + $whistlecost)

Note:

Multiple consecutive unary arithmetic operators are permitted.

3.6 String Concatenation Expressions

[86]    StringConcatExpr    ::=    RangeExpr ( "||" RangeExpr )*

String concatenation expressions allow the string representations of values to be concatenated. In XQuery 3.1, $a || $b is equivalent to fn:concat($a, $b). The following expression evaluates to the string concatenate:

"con" || "cat" || "enate"

3.7 Comparison Expressions

Comparison expressions allow two values to be compared. XQuery 3.1 provides three kinds of comparison expressions, called value comparisons, general comparisons, and node comparisons.

[85]    ComparisonExpr    ::=    StringConcatExpr ( (ValueComp
| GeneralComp
| NodeComp) StringConcatExpr )?
[100]    ValueComp    ::=    "eq" | "ne" | "lt" | "le" | "gt" | "ge"
[99]    GeneralComp    ::=    "=" | "!=" | "<" | "<=" | ">" | ">="
[101]    NodeComp    ::=    "is" | "<<" | ">>"

3.7.1 Value Comparisons

The value comparison operators are eq, ne, lt, le, gt, and ge. Value comparisons are used for comparing single values.

The first step in evaluating a value comparison is to evaluate its operands. The order in which the operands are evaluated is implementation-dependent. Each operand is evaluated by applying the following steps, in order:

  1. Atomization is applied to each operand. The result of this operation is called the atomized operand.

  2. If an atomized operand is an empty sequence, the result of the value comparison is an empty sequence, and the implementation need not evaluate the other operand or apply the operator. However, an implementation may choose to evaluate the other operand in order to determine whether it raises an error.

  3. If an atomized operand is a sequence of length greater than one, a type error is raised [err:XPTY0004].

  4. If an atomized operand is of type xs:untypedAtomic, it is cast to xs:string.

    Note:

    The purpose of this rule is to make value comparisons transitive. Users should be aware that the general comparison operators have a different rule for casting of xs:untypedAtomic operands. Users should also be aware that transitivity of value comparisons may be compromised by loss of precision during type conversion (for example, two xs:integer values that differ slightly may both be considered equal to the same xs:float value because xs:float has less precision than xs:integer).

  5. If the two operands are instances of different primitive types (meaning the 19 primitive types defined in Section 3.2 Primitive datatypesXS2), then:

    1. If each operand is an instance of one of the types xs:string or xs:anyURI, then both operands are cast to type xs:string.

    2. If each operand is an instance of one of the types xs:decimal or xs:float, then both operands are cast to type xs:float.

    3. If each operand is an instance of one of the types xs:decimal, xs:float, or xs:double, then both operands are cast to type xs:double.

    4. Otherwise, a type error is raised [err:XPTY0004].

      Note:

      The primitive type of an xs:integer value for this purpose is xs:decimal.

  6. Finally, if the types of the operands are a valid combination for the given operator, the operator is applied to the operands.

The combinations of atomic types that are accepted by the various value comparison operators, and their respective result types, are listed in B.2 Operator Mapping together with the operator functions that define the semantics of the operator for each type combination. The definitions of the operator functions are found in [XQuery and XPath Functions and Operators 3.1].

Informally, if both atomized operands consist of exactly one atomic value, then 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.

If the types of the operands, after evaluation, are not a valid combination for the given operator, according to the rules in B.2 Operator Mapping, a type error is raised [err:XPTY0004].

Here are some examples of value comparisons:

  • The following comparison atomizes the node(s) that are returned by the expression $book/author. The comparison is true only if the result of atomization is the value "Kennedy" as an instance of xs:string or xs:untypedAtomic. If the result of atomization is an empty sequence, the result of the comparison is an empty sequence. If the result of atomization is a sequence containing more than one value, a type error is raised [err:XPTY0004].

    $book1/author eq "Kennedy"
  • The following comparison is true because atomization converts an array to its member sequence:

    [ "Kennedy" ] eq "Kennedy"
  • The following path expression contains a predicate that selects products whose weight is greater than 100. For any product that does not have a weight subelement, the value of the predicate is the empty sequence, and the product is not selected. This example assumes that weight is a validated element with a numeric type.

    //product[weight gt 100]
  • The following comparisons are true because, in each case, the two constructed nodes have the same value after atomization, even though they have different identities and/or names:

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

    my:hatsize(5) eq my:shoesize(5)
  • The following comparison is true. The eq operator compares two QNames by performing codepoint-comparisons of their namespace URIs and their local names, ignoring their namespace prefixes.

    fn:QName("http://example.com/ns1", "this:color") eq fn:QName("http://example.com/ns1", "that:color")

3.7.2 General Comparisons

The general comparison operators are =, !=, <, <=, >, and >=. 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.

A general comparison is evaluated by applying the following rules, in order:

  1. Atomization is applied to each operand. After atomization, each operand is a sequence of atomic values.

  2. The result of the comparison is true if and only if there is a pair of atomic values, one in the first operand sequence and the other in the second operand sequence, that have the required magnitude relationship. Otherwise the result of the comparison is false or an error. The magnitude relationship between two atomic values is determined by applying the following rules. If a cast operation called for by these rules is not successful, a dynamic error is raised. [err:FORG0001]FO31

    Note:

    The purpose of these rules is to preserve compatibility with XPath 1.0, in which (for example) x < 17 is a numeric comparison if x is an untyped value. Users should be aware that the value comparison operators have different rules for casting of xs:untypedAtomic operands.

    1. If both atomic values are instances of xs:untypedAtomic, then the values are cast to the type xs:string.

    2. If exactly one of the atomic values is an instance of xs:untypedAtomic, it is cast to a type depending on the other value's dynamic type T according to the following rules, in which V denotes the value to be cast:

      1. If T is a numeric type or is derived from a numeric type, then V is cast to xs:double.

      2. If T is xs:dayTimeDuration or is derived from xs:dayTimeDuration, then V is cast to xs:dayTimeDuration.

      3. If T is xs:yearMonthDuration or is derived from xs:yearMonthDuration, then V is cast to xs:yearMonthDuration.

      4. In all other cases, V is cast to the primitive base type of T.

      Note:

      The special treatment of the duration types is required to avoid errors that may arise when comparing the primitive type xs:duration with any duration type.

    3. After performing the conversions described above, 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 and only 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 that have the required magnitude relationship. 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 typed value of any author subelement of $book1 is "Kennedy" as an instance of xs:string or xs:untypedAtomic:

    $book1/author = "Kennedy"
  • The following comparison is true because atomization converts an array to its member sequence:

    [ "Obama", "Nixon", "Kennedy" ] = "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)
  • The following example contains two general comparisons, both of which are true. This example illustrates the fact that the = and != operators are not inverses of each other.

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

3.7.3 Node Comparisons

Node comparisons are used to compare two nodes, by their identity or by their document order. The result of a node comparison is defined by the following rules:

  1. The operands of a node comparison are evaluated in implementation-dependent order.

  2. If either operand is an empty sequence, the result of the comparison is an empty sequence, and the implementation need not evaluate the other operand or apply the operator. However, an implementation may choose to evaluate the other operand in order to determine whether it raises an error.

  3. Each operand must be either a single node or an empty sequence; otherwise a type error is raised [err:XPTY0004].

  4. A comparison with the is operator is true if the two operand nodes are the same node; otherwise it is false. See [XQuery and XPath Data Model (XDM) 3.1] for the definition of node identity.

  5. A comparison with the << operator returns true if the left operand node precedes the right operand node in document order; otherwise it returns false.

  6. A comparison with the >> operator returns true if the left operand node follows the right operand node in document order; otherwise it returns false.

Here are some examples of node comparisons:

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

    /books/book[isbn="1558604820"] is /books/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 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:

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

3.8 Logical Expressions

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

[83]    OrExpr    ::=    AndExpr ( "or" AndExpr )*
[84]    AndExpr    ::=    ComparisonExpr ( "and" ComparisonExpr )*

The first step in evaluating a logical expression is to find the effective boolean value of each of its operands (see 2.4.3 Effective Boolean Value).

The value of an and-expression is determined by the effective boolean values (EBV's) of its operands, as shown in the following table:

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

The value of an or-expression is determined by the effective boolean values (EBV's) of its operands, as shown in the following table:

OR: EBV2 = true EBV2 = false error in EBV2
EBV1 = true true true either true or error
EBV1 = false true false error
error in EBV1 either 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 3.1 provides a function named fn:not that takes a general sequence as parameter and returns a boolean value. The fn:not function is defined in [XQuery and XPath Functions and Operators 3.1]. The fn: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, fn:not raises the same error.

3.9 Node Constructors

XQuery provides node constructors that can create XML nodes within a query.

[140]    NodeConstructor    ::=    DirectConstructor
| ComputedConstructor
[141]    DirectConstructor    ::=    DirElemConstructor
| DirCommentConstructor
| DirPIConstructor
[142]    DirElemConstructor    ::=    "<" QName DirAttributeList ("/>" | (">" DirElemContent* "</" QName S? ">")) /* ws: explicit */
[147]    DirElemContent    ::=    DirectConstructor
| CDataSection
| CommonContent
| ElementContentChar
[228]    ElementContentChar    ::=    (Char - [{}<&])
[148]    CommonContent    ::=    PredefinedEntityRef | CharRef | "{{" | "}}" | EnclosedExpr
[153]    CDataSection    ::=    "<![CDATA[" CDataSectionContents "]]>" /* ws: explicit */
[154]    CDataSectionContents    ::=    (Char* - (Char* ']]>' Char*)) /* ws: explicit */
[143]    DirAttributeList    ::=    (S (QName S? "=" S? DirAttributeValue)?)* /* ws: explicit */
[144]    DirAttributeValue    ::=    ('"' (EscapeQuot | QuotAttrValueContent)* '"')
| ("'" (EscapeApos | AposAttrValueContent)* "'")
/* ws: explicit */
[145]    QuotAttrValueContent    ::=    QuotAttrContentChar
| CommonContent
[146]    AposAttrValueContent    ::=    AposAttrContentChar
| CommonContent
[229]    QuotAttrContentChar    ::=    (Char - ["{}<&])
[230]    AposAttrContentChar    ::=    (Char - ['{}<&])
[226]    EscapeQuot    ::=    '""'
[227]    EscapeApos    ::=    "''"
[36]    EnclosedExpr    ::=    "{" Expr? "}"

Constructors are provided for element, attribute, document, text, comment, and processing instruction nodes. Two kinds of constructors are provided: direct constructors, which use an XML-like notation that can incorporate enclosed expressions, and computed constructors, which use a notation based on enclosed expressions.

The rest of 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 here.

3.9.1 Direct Element Constructors

An element constructor creates an element node. [Definition: A direct element constructor is a form of element constructor in which the name of the constructed element is a constant.] Direct element constructors are based on standard XML notation. For example, the following expression is a direct element constructor that creates a book element containing an attribute and some nested elements:

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

If the element name in a direct element constructor has a namespace prefix, the namespace prefix is resolved to a namespace URI using the statically known namespaces. If the element name has no namespace prefix, it is implicitly qualified by the default element/type namespace. Note that both the statically known namespaces and the default element/type namespace may be affected by namespace declaration attributes found inside the element constructor. The namespace prefix of the element name is retained after expansion of the lexical QName , as described in [XQuery and XPath Data Model (XDM) 3.1]. The resulting expanded QName becomes the node-name property of the constructed element node.

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 [err:XQST0118].

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

<example>
   <p> Here is a query. </p>
   <eg> $b/title </eg>
   <p> Here is the result of the query. </p>
   <eg>{ $b/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> $b/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 "}".) Alternatively, the character references &#x7b; and &#x7d; can be used to denote curly brace characters. 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:XPST0003].

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.

3.9.1.1 Attributes

The start tag of a direct element constructor may contain one or more attributes. As in XML, each attribute is specified by a name and a value. In a direct element constructor, the name of each attribute is specified by a constant lexical 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 enclosed expressions, 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. However, note that namespace declaration attributes (see 3.9.1.2 Namespace Declaration Attributes) do not create attribute nodes.

If an attribute name has a namespace prefix, the prefix is resolved to a namespace URI using the statically known namespaces. If the attribute name has no namespace prefix, the attribute is in no namespace. Note that the statically known namespaces used in resolving an attribute name may be affected by namespace declaration attributes that are found inside the same element constructor. The namespace prefix of the attribute name is retained after expansion of the lexical QName, as described in [XQuery and XPath Data Model (XDM) 3.1]. The resulting expanded QName becomes the node-name property of the constructed attribute node.

If the attributes in a direct element constructor do not have distinct expanded QNames as their respective node-name properties, a static error is raised [err:XQST0040].

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

  1. Each consecutive sequence of literal characters in the attribute content is processed as a string literal containing those characters, with the following exceptions:

    1. Each occurrence of two consecutive { characters is replaced by a single { character.

    2. Each occurrence of two consecutive } characters is replaced by a single } character.

    3. Each occurrence of EscapeQuot is replaced by a single " character.

    4. Each occurrence of EscapeApos is replaced by a single ' character.

    Attribute value normalization is then applied to normalize whitespace and expand character references and predefined entity references. The rules for attribute value normalization are the rules from Section 3.3.3 of [XML 1.0] or Section 3.3.3 of [XML 1.1] (it is implementation-defined which version is used). The rules are applied as though the type of the attribute were CDATA (leading and trailing whitespace characters are not stripped.)

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

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

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

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

  3. Adjacent strings resulting from the above steps are concatenated with no intervening blanks. The resulting string becomes the string-value property of the attribute node. The attribute node is given a type annotation of xs:untypedAtomic (this type annotation may change if the parent element is validated). The typed-value property of the attribute node is the same as its string-value, as an instance of xs:untypedAtomic.

  4. The parent property of the attribute node is set to the element node constructed by the direct element constructor that contains this attribute.

  5. If the attribute name is xml:id, then xml:id processing is performed as defined in [XML ID]. This ensures that the attribute has the type xs:ID and that its value is properly normalized. If an error is encountered during xml:id processing, an implementation may raise a dynamic error [err:XQDY0091].

  6. If the attribute name is xml:id, the is-id property of the resulting attribute node is set to true; otherwise the is-id property is set to false. The is-idrefs property of the attribute node is unconditionally set to false.

  • Example:

    <shoe size="7"/>

    The string value of the size attribute is "7".

  • Example:

    <shoe size="{7}"/>

    The string value of the size attribute is "7".

  • Example:

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

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

  • Example:

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

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

  • Example:

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

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

3.9.1.2 Namespace Declaration Attributes

The names of a constructed element and its attributes may be lexical QNames that include namespace prefixes. Namespace prefixes can be bound to namespaces in the Prolog or by namespace declaration attributes. It is a static error to use a namespace prefix that has not been bound to a namespace [err:XPST0081].

[Definition: A namespace declaration attribute is used inside a direct element constructor. Its purpose is to bind a namespace prefix or to set the default element/type namespace for the constructed element node, including its attributes.] Syntactically, a namespace declaration attribute has the form of an attribute with namespace prefix xmlns, or with name xmlns and no namespace prefix. All the namespace declaration attributes of a given element must have distinct names [err:XQST0071]. Each namespace declaration attribute is processed as follows:

  • The value of the namespace declaration attribute (a DirAttributeValue) is processed as follows. If the DirAttributeValue contains an EnclosedExpr, a static error is raised [err:XQST0022]. Otherwise, it is processed as described in rule 1 of 3.9.1.1 Attributes. An implementation may raise a static error [err:XQST0046] if the resulting value is of nonzero length and is neither an absolute URI nor a relative URI. The resulting value is used as the namespace URI in the following rules.

  • If the prefix of the attribute name is xmlns, then the local part of the attribute name is interpreted as a namespace prefix. This prefix and the namespace URI are added to the statically known namespaces of the constructor expression (overriding any existing binding of the given prefix), and are also added as a namespace binding to the in-scope namespaces of the constructed element. If the namespace URI is a zero-length string and the implementation supports [XML Names 1.1], any existing namespace binding for the given prefix is removed from the in-scope namespaces of the constructed element and from the statically known namespaces of the constructor expression. If the namespace URI is a zero-length string and the implementation does not support [XML Names 1.1], a static error is raised [err:XQST0085]. It is implementation-defined whether an implementation supports [XML Names] or [XML Names 1.1].

  • If the name of the namespace declaration attribute is xmlns with no prefix, then the namespace URI specifies the default element/type namespace of the constructor expression (overriding any existing default), and is added (with no prefix) to the in-scope namespaces of the constructed element (overriding any existing namespace binding with no prefix). If the namespace URI is a zero-length string, the default element/type namespace of the constructor expression is set to absentDM31, and any no-prefix namespace binding is removed from the in-scope namespaces of the constructed element.

  • It is a static error [err:XQST0070] if a namespace declaration attribute attempts to do any of the following:

    • Bind the prefix xml to some namespace URI other than http://www.w3.org/XML/1998/namespace.

    • Bind a prefix other than xml to the namespace URI http://www.w3.org/XML/1998/namespace.

    • Bind the prefix xmlns to any namespace URI.

    • Bind a prefix to the namespace URI http://www.w3.org/2000/xmlns/.

A namespace declaration attribute does not cause an attribute node to be created.

The following examples illustrate namespace declaration attributes:

  • In this element constructor, a namespace declaration attribute is used to set the default element/type namespace to http://example.org/animals:

    <cat xmlns = "http://example.org/animals">
      <breed>Persian</breed>
    </cat>
  • In this element constructor, namespace declaration attributes are used to bind 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>
3.9.1.3 Content

The part of a direct element constructor between the start tag and the end tag is called the content of the element constructor. This content may consist of text characters (parsed as ElementContentChar), nested direct constructors, CDataSections, character and predefined entity references, and enclosed expressions. In general, the value of an enclosed expression may be any sequence of nodes and/or atomic values. Enclosed expressions can be used in the content of an element constructor to compute both the content and the attributes of the constructed node.

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

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

    1. If the boundary-space policy in the static context is strip, boundary whitespace is identified and deleted (see 3.9.1.4 Boundary Whitespace for the definition of boundary whitespace.)

    2. Predefined entity references and character references are expanded into their referenced strings, as described in 3.1.1 Literals. Characters inside a CDataSection, including special characters such as < and &, are treated as literal characters rather than as markup characters (except for the sequence ]]>, which terminates the CDataSection).

    3. Each consecutive sequence of literal characters evaluates to a single text node containing the characters.

    4. Each nested direct constructor is evaluated according to the rules in 3.9.1 Direct Element Constructors or 3.9.2 Other Direct Constructors, resulting in a new element, comment, or processing instruction node. Then:

      1. The parent property of the resulting node is then set to the newly constructed element node.

      2. The base-uri property of the resulting node, and of each of its descendants, is set to be the same as that of its new parent, unless it (the child node) has an xml:base attribute, in which case its base-uri property is set to the value of that attribute, resolved (if it is relative) against the base-uri property of its new parent node.

    5. Enclosed expressions are evaluated as follows:

      1. Each array returned by the enclosed expression is flattened by calling the function array:flatten() before the steps that follow.

      2. If an enclosed expression returns a functionDM31, a type error is raised [err:XQTY0105].

      3. 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 space character inserted between adjacent values.

        Note:

        The insertion of blank characters between adjacent values applies even if one or both of the values is a zero-length string.

      4. For each node returned by an enclosed expression, a new copy is made of the given node and all nodes that have the given node as an ancestor, collectively referred to as copied nodes. The properties of the copied nodes are as follows:

        1. Each copied node receives a new node identity.

        2. The parent, children, and attributes properties of the copied nodes are set so as to preserve their inter-node relationships. For the topmost node (the node directly returned by the enclosed expression), the parent property is set to the node constructed by this constructor.

        3. If construction mode in the static context is strip:

          1. If the copied node is an element node, its type annotation is set to xs:untyped. Its nilled, is-id, and is-idrefs properties are set to false.

          2. If the copied node is an attribute node, its type-name property is set to xs:untypedAtomic. Its is-idrefs property is set to false. Its is-id property is set to true if the qualified name of the attribute node is xml:id; otherwise it is set to false.

          3. The string-value of each copied element and attribute node remains unchanged, and its typed-value becomes equal to its string-value as an instance of xs:untypedAtomic.

            Note:

            Implementations that store only the typed value of a node are required at this point to convert the typed value to a string form.

          On the other hand, if construction mode in the static context is preserve, the type-name, nilled, string-value, typed-value, is-id, and is-idrefs properties of the copied nodes are preserved.

        4. The in-scope-namespaces property of a copied element node is determined by the following rules. In applying these rules, the default namespace or absence of a default namespace is treated like any other namespace binding:

          1. If copy-namespaces mode specifies preserve, all in-scope-namespaces of the original element are retained in the new copy. If copy-namespaces mode specifies no-preserve, the new copy retains only those in-scope namespaces of the original element that are used in the names of the element and its attributes.

          2. If copy-namespaces mode specifies inherit, the copied node inherits all the in-scope namespaces of the constructed node, augmented and overridden by the in-scope namespaces of the original element that were preserved by the preceding rule. If copy-namespaces mode specifies no-inherit, the copied node does not inherit any in-scope namespaces from the constructed node.

        5. An enclosed expression in the content of an element constructor may cause one or more existing nodes to be copied. Type error [err:XQTY0086] is raised in the following cases:

          1. An element node is copied, and the typed value of the element node or one of its attributes is namespace-sensitive, and construction mode is preserve, and copy-namespaces mode is no-preserve.

          2. An attribute node is copied but its parent element node is not copied, and the typed value of the copied attribute node is namespace-sensitive, and construction mode is preserve.

          Note:

          The rationale for error [err:XQTY0086] is as follows: It is not possible to preserve the type of a QName without also preserving the namespace binding that defines the prefix of the QName.

        6. When an element or processing instruction node is copied, its base-uri property is set to be the same as that of its new parent, with the following exception: if a copied element node has an xml:base attribute, its base-uri property is set to the value of that attribute, resolved (if it is relative) against the base-uri property of the new parent node.

        7. All other properties of the copied nodes are preserved.

  2. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

  3. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

  4. If the content sequence contains an attribute node or a namespace node following a node that is not an attribute node or a namespace node, a type error is raised [err:XQTY0024].

  5. The properties of the newly constructed element node are determined as follows:

    1. node-name is the expanded QName resulting from resolving the element name in the start tag, including its original namespace prefix (if any), as described in 3.9.1 Direct Element Constructors.

    2. parent is set to empty.

    3. attributes consist of all the attributes specified in the start tag as described in 3.9.1.1 Attributes, together with all the attribute nodes in the content sequence, in implementation-dependent order. Note that the parent property of each of these attribute nodes has been set to the newly constructed element node. If two or more attributes have the same node-name, a dynamic error is raised [err:XQDY0025]. If an attribute named xml:space has a value other than preserve or default, a dynamic error may be raised [err:XQDY0092].

    4. children consist of all the element, text, comment, and processing instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed element node.

    5. base-uri is set to the following value:

      1. If the constructed node has an attribute named xml:base, then the value of this attribute, resolved (if it is relative) against the Static Base URI, as described in 2.4.6 Resolving a Relative URI Reference.

      2. Otherwise, the Static Base URI.

    6. in-scope-namespaces consist of all the namespace bindings resulting from namespace declaration attributes as described in 3.9.1.2 Namespace Declaration Attributes, and possibly additional namespace bindings as described in 3.9.4 In-scope Namespaces of a Constructed Element.

    7. The nilled property is false.

    8. The string-value property is equal to the concatenated contents of the text-node descendants in document order. If there are no text-node descendants, the string-value property is a zero-length string.

    9. The typed-value property is equal to the string-value property, as an instance of xs:untypedAtomic.

    10. If construction mode in the static context is strip, the type-name property is xs:untyped. On the other hand, if construction mode is preserve, the type-name property is xs:anyType.

    11. The is-id and is-idrefs properties are set to false.

  • Example:

    <a>{1}</a>

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

  • Example:

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

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

  • Example:

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

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

  • Example:

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

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

  • Example:

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

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

  • Example:

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

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

  • Example:

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

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

3.9.1.4 Boundary Whitespace

In a direct element constructor, whitespace characters may appear in the content of the constructed element. 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>

[Definition: Boundary whitespace is a sequence of consecutive whitespace characters within the content of a direct element constructor, that is delimited at each end either by the start or end of the content, or by a DirectConstructor, or by an EnclosedExpr. For this purpose, characters generated by character references such as &#x20; or by CDataSections are not considered to be whitespace characters.]

The boundary-space policy in the static context controls whether boundary whitespace is preserved by element constructors. If boundary-space policy is strip, boundary whitespace is not considered significant and is discarded. On the other hand, if boundary-space policy is preserve, 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 will be stripped away by the element constructor if boundary-space policy is strip.

  • Example:

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

    If boundary-space policy is strip, this example is equivalent to <a>abc</a>. However, if boundary-space policy is preserve, 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>.

  • Example:

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

    This example is equivalent to <a> abc</a>, regardless of the boundary-space policy, because the space generated by the character reference is not treated as a whitespace character.

  • Example:

    <a>{"  "}</a>

    This example constructs an element containing two space characters, regardless of the boundary-space policy, because whitespace inside an enclosed expression is never considered to be boundary whitespace.

  • Example:

    <a>{ [ "one", "little", "fish" ] }</a>

    This example constructs an element containing the text one little fish, because the array is flattened, and the resulting sequence of atomic values is converted to a text node with a single blank between values.

Note:

Element constructors treat attributes named xml:space as ordinary attributes. An xml:space attribute does not affect the handling of whitespace by an element constructor.

3.9.2 Other Direct Constructors

XQuery allows an expression to generate a processing instruction node or a comment node. This can be accomplished by using a direct processing instruction constructor or a direct comment constructor. In each case, the syntax of the constructor expression is based on the syntax of a similar construct in XML.

[151]    DirPIConstructor    ::=    "<?" PITarget (S DirPIContents)? "?>" /* ws: explicit */
[152]    DirPIContents    ::=    (Char* - (Char* '?>' Char*)) /* ws: explicit */
[149]    DirCommentConstructor    ::=    "<!--" DirCommentContents "-->" /* ws: explicit */
[150]    DirCommentContents    ::=    ((Char - '-') | ('-' (Char - '-')))* /* ws: explicit */

A direct processing instruction constructor creates a processing instruction node whose target property is PITarget and whose content property is DirPIContents. The base-uri property of the node is empty. The parent property of the node is empty.

The PITarget of a processing instruction must not consist of the characters "XML" in any combination of upper and lower case. The DirPIContents of a processing instruction must not contain the string "?>".

The following example illustrates a direct processing instruction constructor:

<?format role="output" ?>

A direct comment constructor creates a comment node whose content property is DirCommentContents. Its parent property is empty.

The DirCommentContents of a comment must not contain two consecutive hyphens or end with a hyphen. These rules are syntactically enforced by the grammar shown above.

The following example illustrates a direct comment constructor:

<!-- Tags are ignored in the following section -->

Note:

A direct comment constructor is different from a comment, since a direct comment constructor actually constructs a comment node, whereas a comment is simply used in documenting a query and is not evaluated.

3.9.3 Computed Constructors

[155]    ComputedConstructor    ::=    CompDocConstructor
| CompElemConstructor
| CompAttrConstructor
| CompNamespaceConstructor
| CompTextConstructor
| CompCommentConstructor
| CompPIConstructor

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, processing-instruction, comment, or namespace.

For those kinds of nodes that have names (element, attribute, and processing instruction 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 an EQName or as an expression enclosed in braces. [Definition: When an expression is used to specify the name of a constructed node, that expression is called the name expression of the constructor.]

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 3.9.1 Direct Element Constructors:

element book {
   attribute isbn {"isbn-0060229357" },
   element title { "Harold and the Purple Crayon"},
   element author {
      element first { "Crockett" },
      element last {"Johnson" }
   }
}
3.9.3.1 Computed Element Constructors
[157]    CompElemConstructor    ::=    "element" (EQName | ("{" Expr "}")) EnclosedContentExpr
[218]    EQName    ::=    QName | URIQualifiedName
[158]    EnclosedContentExpr    ::=    EnclosedExpr
[36]    EnclosedExpr    ::=    "{" Expr? "}"

[Definition: A computed element constructor creates an element node, allowing both the name and the content of the node to be computed.]

If the keyword element is followed by an EQName, it is expanded to an expanded QName as follows: if the EQName has a BracedURILiteral it is expanded using the specified URI; if the EQName is a lexical QName with a namespace prefix it is expanded using the statically known namespaces; if the EQName is a lexical QName without a prefix it is implicitly qualified by the default element/type namespace. The resulting expanded QName is used as the node-name property of the constructed element node. If expansion of the QName is not successful, a static error is raised [err:XPST0081].

If the keyword element is followed by a name expression, the name expression is processed as follows:

  1. Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic value of type xs:QName, xs:string, or xs:untypedAtomic, a type error is raised [err:XPTY0004].

  2. If the atomized value of the name expression is of type xs:QName, that expanded QName is used as the node-name property of the constructed element, retaining the prefix part of the QName.

  3. If the atomized value of the name expression is of type xs:string or xs:untypedAtomic, that value is converted to an expanded QName. If the string value contains a namespace prefix, that prefix is resolved to a namespace URI using the statically known namespaces. If the string value contains no namespace prefix, it is treated as a local name in the default element/type namespace. The resulting expanded QName is used as the node-name property of the constructed element, retaining the prefix part of the QName. If conversion of the atomized name expression to an expanded QName is not successful, a dynamic error is raised [err:XQDY0074].

A dynamic error is raised [err:XQDY0096] if the node-name of the constructed element node has any of the following properties:

  • Its namespace prefix is xmlns.

  • Its namespace URI is http://www.w3.org/2000/xmlns/.

  • Its namespace prefix is xml and its namespace URI is not http://www.w3.org/XML/1998/namespace.

  • Its namespace prefix is other than xml and its namespace URI is http://www.w3.org/XML/1998/namespace.

The content expression of a computed element constructor (if present) is processed in exactly the same way as an enclosed expression in the content of a direct element constructor, as described in Step 1e of 3.9.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. If the content expression is absent, the content sequence is an empty sequence.

Processing of the computed element constructor proceeds as follows:

  1. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

  2. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

  3. If the content sequence contains an attribute node or a namespace node following a node that is not an attribute node or a namespace node, a type error is raised [err:XQTY0024].

  4. The properties of the newly constructed element node are determined as follows:

    1. node-name is the expanded QName resulting from processing the specified lexical QName or name expression, as described above.

    2. parent is empty.

    3. attributes consist of all the attribute nodes in the content sequence, in implementation-dependent order. Note that the parent property of each of these attribute nodes has been set to the newly constructed element node. If two or more attributes have the same node-name, a dynamic error is raised [err:XQDY0025]. If an attribute named xml:space has a value other than preserve or default, a dynamic error may be raised [err:XQDY0092].

    4. children consist of all the element, text, comment, and processing instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed element node.

    5. base-uri is set to the following value:

      1. If the constructed node has an attribute named xml:base, then the value of this attribute, resolved (if it is relative) against the Static Base URI, as described in 2.4.6 Resolving a Relative URI Reference.

      2. Otherwise, the Static Base URI.

    6. in-scope-namespaces are computed as described in 3.9.4 In-scope Namespaces of a Constructed Element.

    7. The nilled property is false.

    8. The string-value property is equal to the concatenated contents of the text-node descendants in document order.

    9. The typed-value property is equal to the string-value property, as an instance of xs:untypedAtomic.

    10. If construction mode in the static context is strip, the type-name property is xs:untyped. On the other hand, if construction mode is preserve, the type-name property is xs:anyType.

    11. The is-id and is-idrefs properties are set to false.

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 {fn:node-name($e)}
   {$e/@*, 2 * fn: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>.

Note:

The static type of the expression fn:node-name($e) is xs:QName?, denoting zero or one QName. Therefore, if the Static Typing Feature is in effect, the above example raises a static type error, since the name expression in a computed element constructor is required to return exactly one string or QName. In order to avoid the static type error, the name expression fn:node-name($e) could be rewritten as fn:exactly-one(fn:node-name($e)). If the Static Typing Feature is not in effect, the example can be successfully evaluated as written, provided that $e is bound to exactly one element node with numeric content.

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 dictionary element containing a sequence of entry elements, each of which encodes translations for a specific word. Here is an example entry that encodes the German and Italian variants of the word "address":

<entry word="address">
   <variant xml:lang="de">Adresse</variant>
   <variant xml:lang="it">indirizzo</variant>
</entry>

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

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

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

  element
    {$dict/entry[@word=name($e)]/variant[@xml:lang="it"]}
    {$e/@*, $e/node()}

The result of this expression is as follows:

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

Note:

As in the previous example, if the Static Typing Feature is in effect, the enclosed expression that computes the element name in the above computed element constructor must be wrapped in a call to the fn:exactly-one function in order to avoid a static type error.

Additional examples of computed element constructors can be found in I.3 Recursive Transformations.

3.9.3.2 Computed Attribute Constructors
[159]    CompAttrConstructor    ::=    "attribute" (EQName | ("{" Expr "}")) EnclosedExpr
[218]    EQName    ::=    QName | URIQualifiedName
[36]    EnclosedExpr    ::=    "{" Expr? "}"

A computed attribute constructor creates a new attribute node, with its own node identity.

Attributes have no default namespace. The rules that expand attribute names create an implementation-dependent prefix if an attribute name has a namespace URI but no prefix is provided.

If the keyword attribute is followed by an EQName, it is expanded to an expanded QName as follows:

The resulting expanded QName (including its prefix) is used as the node-name property of the constructed attribute node. If expansion of the QName is not successful, a static error is raised [err:XPST0081].

If the keyword attribute is followed by a name expression, the name expression is processed as follows:

  1. Atomization is applied to the result of the name expression. If the result of atomization is not a single atomic value of type xs:QName, xs:string, or xs:untypedAtomic, a type error is raised [err:XPTY0004].

  2. If the atomized value of the name expression is of type xs:QName:

    1. If the expanded QName returned by the atomized name expression has a namespace URI but has no prefix, it is given an implementation-dependent prefix.

    2. The resulting expanded QName (including its prefix) is used as the node-name property of the constructed attribute node.

  3. If the atomized value of the name expression is of type xs:string or xs:untypedAtomic, that value is converted to an expanded QName. If the string value contains a namespace prefix, that prefix is resolved to a namespace URI using the statically known namespaces. If the string value contains no namespace prefix, it is treated as a local name in no namespace. The resulting expanded QName (including its prefix) is used as the node-name property of the constructed attribute. If conversion of the atomized name expression to an expanded QName is not successful, a dynamic error is raised [err:XQDY0074].

A dynamic error is raised [err:XQDY0044] if the node-name of the constructed attribute node has any of the following properties:

  • Its namespace prefix is xmlns.

  • It has no namespace prefix and its local name is xmlns.

  • Its namespace URI is http://www.w3.org/2000/xmlns/.

  • Its namespace prefix is xml and its namespace URI is not http://www.w3.org/XML/1998/namespace.

  • Its namespace prefix is other than xml and its namespace URI is http://www.w3.org/XML/1998/namespace.

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

  1. Atomization is applied to the result of the content expression, converting it to a sequence of atomic values. (If the content expression is absent, the result of this step is an empty sequence.)

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

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. The resulting string becomes the string-value property of the new attribute node. The type annotation (type-name property) of the new attribute node is xs:untypedAtomic. The typed-value property of the attribute node is the same as its string-value, as an instance of xs:untypedAtomic.

  4. The parent property of the attribute node is set to empty.

  5. If the attribute name is xml:id, then xml:id processing is performed as defined in [XML ID]. This ensures that the attribute node has the type xs:ID and that its value is properly normalized. If an error is encountered during xml:id processing, an implementation may raise a dynamic error [err:XQDY0091].

  6. If the attribute name is xml:id, the is-id property of the resulting attribute node is set to true; otherwise the is-id property is set to false. The is-idrefs property of the attribute node is unconditionally set to false.

  7. If the attribute name is xml:space and the attribute value is other than preserve or default, a dynamic error may be raised [err:XQDY0092].

  • Example:

    attribute size {4 + 3}

    The string value of the size attribute is "7" and its type is xs:untypedAtomic.

  • 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 string value is "Hello 1 2 3 Goodbye".

3.9.3.3 Document Node Constructors
[156]    CompDocConstructor    ::=    "document" EnclosedExpr
[36]    EnclosedExpr    ::=    "{" Expr? "}"

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

The content expression of a document node constructor is processed in exactly the same way as an enclosed expression in the content of a direct element constructor, as described in Step 1e of 3.9.1.3 Content. The result of processing the content expression is a sequence of nodes called the content sequence. Processing of the document node constructor then proceeds as follows:

  1. If the content sequence contains a document node, the document node is replaced in the content sequence by its children.

  2. Adjacent text nodes in the content sequence are merged into a single text node by concatenating their contents, with no intervening blanks. After concatenation, any text node whose content is a zero-length string is deleted from the content sequence.

  3. If the content sequence contains an attribute node, a type error is raised [err:XPTY0004].

  4. If the content sequence contains a namespace node, a type error is raised [err:XPTY0004].

  5. The properties of the newly constructed document node are determined as follows:

    1. base-uri is set to the Static Base URI.

    2. children consist of all the element, text, comment, and processing instruction nodes in the content sequence. Note that the parent property of each of these nodes has been set to the newly constructed document node.

    3. The unparsed-entities and document-uri properties are empty.

    4. The string-value property is equal to the concatenated contents of the text-node descendants in document order.

    5. The typed-value property is equal to the string-value property, as an instance of xs:untypedAtomic.

No validation is performed on the constructed document node. The [XML 1.0] rules that govern the structure of an XML document (for example, the document node must have exactly one child that is an element node) are not enforced by the XQuery document node constructor.

3.9.3.4 Text Node Constructors
[164]    CompTextConstructor    ::=    "text" EnclosedExpr
[36]    EnclosedExpr    ::=    "{" Expr? "}"

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

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

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

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

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

The parent property of the constructed text node is set to empty.

Note:

It is possible for a text node constructor to construct a text node containing a zero-length string. However, if used in the content of a constructed element or document node, such a text node will be deleted or merged with another text node.

The following example illustrates a text node constructor:

text {"Hello"}
3.9.3.5 Computed Processing Instruction Constructors
[166]    CompPIConstructor    ::=    "processing-instruction" (NCName | ("{" Expr "}")) EnclosedExpr
[36]    EnclosedExpr    ::=    "{" Expr? "}"

A computed processing instruction constructor (CompPIConstructor) constructs a new processing instruction node with its own node identity.

If the keyword processing-instruction is followed by an NCName, that NCName is used as the target property of the constructed node. If the keyword processing-instruction is followed by a name expression, the name expression is processed as follows:

  1. Atomization is applied to the value of the name expression. If the result of atomization is not a single atomic value of type xs:NCName, xs:string, or xs:untypedAtomic, a type error is raised [err:XPTY0004].

  2. If the atomized value of the name expression is of type xs:string or xs:untypedAtomic, that value is cast to the type xs:NCName. If the value cannot be cast to xs:NCName, a dynamic error is raised [err:XQDY0041].

  3. The resulting NCName is then used as the target property of the newly constructed processing instruction node. However, a dynamic error is raised if the NCName is equal to "XML" (in any combination of upper and lower case) [err:XQDY0064].

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

  1. Atomization is applied to the value of the content expression, converting it to a sequence of atomic values. (If the content expression is absent, the result of this step is an empty sequence.)

  2. 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. If any of the resulting strings contains the string "?>", a dynamic error [err:XQDY0026] is raised.

  3. The individual strings resulting from the previous step are merged into a single string by concatenating them with a single space character between each pair. Leading whitespace is removed from the resulting string. The resulting string then becomes the content property of the constructed processing instruction node.

The remaining properties of the new processing instruction node are determined as follows:

  1. The parent property is empty.

  2. The base-uri property is empty.

The following example illustrates a computed processing instruction constructor:

let $target := "audio-output",
    $content := "beep"
return processing-instruction {$target} {$content}

The processing instruction node constructed by this example might be serialized as follows:

<?audio-output beep?>
3.9.3.6 Computed Comment Constructors
[165]    CompCommentConstructor    ::=    "comment" EnclosedExpr
[36]    EnclosedExpr    ::=    "{" Expr? "}"

A computed comment constructor (CompCommentConstructor) constructs a new comment node with its own node identity. The content expression of a computed comment constructor is processed as follows:

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

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

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

  4. It is a dynamic error [err:XQDY0072] if the result of the content expression of a computed comment constructor contains two adjacent hyphens or ends with a hyphen.

The parent property of the constructed comment node is set to empty.

The following example illustrates a computed comment constructor:

let $homebase := "Houston"
return comment {fn:concat($homebase, ", we have a problem.")}

The comment node constructed by this example might be serialized as follows:

<!--Houston, we have a problem.-->
3.9.3.7 Computed Namespace Constructors
[160]    CompNamespaceConstructor    ::=    "namespace" (Prefix | EnclosedPrefixExpr) EnclosedURIExpr
[161]    Prefix    ::=    NCName
[162]    EnclosedPrefixExpr    ::=    EnclosedExpr
[163]    EnclosedURIExpr    ::=    EnclosedExpr
[36]    EnclosedExpr    ::=    "{" Expr? "}"

A computed namespace constructor creates a new namespace node, with its own node identity. The parent of the newly created namespace node is empty.

If the constructor specifies a Prefix, it is used as the prefix for the namespace node.

If the constructor specifies a PrefixExpr, the prefix expression is evaluated as follows:

  1. Atomization is applied to the result of the PrefixExpr.

  2. If the result of atomization is an empty sequence or a single atomic value of type xs:string or xs:untypedAtomic, then the following rules are applied in order:

    1. If the result is castable to xs:NCName, then it is used as the local name of the newly constructed namespace node. (The local name of a namespace node represents the prefix part of the namespace binding.)

    2. If the result is the empty sequence or a zero-length xs:string or xs:untypedAtomic value, the new namespace node has no name (such a namespace node represents a binding for the default namespace).

    3. Otherwise, a dynamic error is raised [err:XQDY0074].

  3. If the result of atomization is not an empty sequence or a single atomic value of type xs:string or xs:untypedAtomic, a type error is raised [err:XPTY0004].

The content expression is evaluated, and the result is cast to xs:anyURI to create the URI property for the newly created node. An implementation may raise a dynamic error [err:XQDY0074] if the URIExpr of a computed namespace constructor is not a valid instance of xs:anyURI.

An error [err:XQDY0101] is raised if a computed namespace constructor attempts to do any of the following:

  • Bind the prefix xml to some namespace URI other than http://www.w3.org/XML/1998/namespace.

  • Bind a prefix other than xml to the namespace URI http://www.w3.org/XML/1998/namespace.

  • Bind the prefix xmlns to any namespace URI.

  • Bind a prefix to the namespace URI http://www.w3.org/2000/xmlns/.

  • Bind any prefix (including the empty prefix) to a zero-length namespace URI.

By itself, a computed namespace constructor has no effect on in-scope namespaces, but if an element constructor's content sequence contains a namespace node, the namespace binding it represents is added to the element's in-scope namespaces.

A computed namespace constructor has no effect on the statically known namespaces.

Note:

The newly created namespace node has all properties defined for a namespace node in the data model. As defined in the data model, the name of the node is the prefix, the string value of the node is the URI, the relative order of nodes that share no common ancestor is implementation dependent, and the relative order of namespace nodes that share a parent is also implementation dependent.

Examples:

  • A computed namespace constructor with a prefix:

    namespace a {"http://a.example.com" }
  • A computed namespace constructor with a prefix expression:

    namespace {"a"} {"http://a.example.com" }
  • A computed namespace constructor with an empty prefix:

    namespace { "" } {"http://a.example.com" }

Computed namespace constructors are generally used to add to the in-scope namespaces of elements created with element constructors:

<age xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"> {
  namespace xs {"http://www.w3.org/2001/XMLSchema"},
  attribute xsi:type {"xs:integer"},
  23
}</age>

In the above example, note that the xsi namespace binding is created for the element because it is used in an attribute name. The attribute's content is simply character data, and has no effect on namespace bindings. The computed namespace constructor ensures that the xs binding is created.

Computed namespace constructors have no effect on the statically known namespaces. If the prefix a is not already defined in the statically known namespaces, the following expression results in a static error [err:XPST0081].

<a:form>
 {
  namespace a { "http://a.example.com" }
 }
</a:form>

3.9.4 In-scope Namespaces of a Constructed Element

An element node constructed by a direct or computed element constructor has an in-scope namespaces property that consists of a set of namespace bindings. The in-scope namespaces of an element node may affect the way the node is serialized (see 2.2.4 Serialization), and may also affect the behavior of certain functions that operate on nodes, such as fn:name. Note the difference between in-scope namespaces, which is a dynamic property of an element node, and statically known namespaces, which is a static property of an expression. Also note that one of the namespace bindings in the in-scope namespaces may have no prefix (denoting the default namespace for the given element). The in-scope namespaces of a constructed element node consist of the following namespace bindings:

  • A namespace binding is created for each namespace declared in the current element constructor by a namespace declaration attribute.

  • A namespace binding is created for each namespace node in the content sequence of the current element constructor.

  • A namespace binding is created for each namespace that is declared in a namespace declaration attribute of an enclosing direct element constructor and not overridden by the current element constructor or an intermediate constructor.

  • A namespace binding is always created to bind the prefix xml to the namespace URI http://www.w3.org/XML/1998/namespace.

  • For each prefix used in the name of the constructed element or in the names of its attributes, a namespace binding must exist. If a namespace binding does not already exist for one of these prefixes, a new namespace binding is created for it. If this would result in a conflict, because it would require two different bindings of the same prefix, then the prefix used in the node name is changed to an arbitrary implementation-dependent prefix that does not cause such a conflict, and a namespace binding is created for this new prefix. If there is an in-scope default namespace, then a binding is created between the empty prefix and that URI.

Note:

Copy-namespaces mode does not affect the namespace bindings of a newly constructed element node. It applies only to existing nodes that are copied by a constructor expression.

In an element constructor, if two or more namespace bindings in the in-scope bindings would have the same prefix, then an error is raised if they have different URIs [err:XQDY0102]; if they would have the same prefix and URI, duplicate bindings are ignored. If the name of an element in an element constructor is in no namespace, creating a default namespace for that element using a computed namespace constructor is an error [err:XQDY0102]. For instance, the following computed constructor raises an error because the element's name is not in a namespace, but a default namespace is defined.

element e { namespace {''} {'u'} }

The following query illustrates the in-scope namespaces of a constructed element:

declare namespace p="http://example.com/ns/p";
declare namespace q="http://example.com/ns/q";
declare namespace f="http://example.com/ns/f";

<p:a q:b="{f:func(2)}" xmlns:r="http://example.com/ns/r"/>

The in-scope namespaces of the resulting p:a element consists of the following namespace bindings:

  • p = "http://example.com/ns/p"

  • q = "http://example.com/ns/q"

  • r = "http://example.com/ns/r"

  • xml = "http://www.w3.org/XML/1998/namespace"

The namespace bindings for p and q are added to the result element because their respective namespaces are used in the names of the element and its attributes. The namespace binding r="http://example.com/ns/r" is added to the in-scope namespaces of the constructed element because it is defined by a namespace declaration attribute, even though it is not used in a name.

No namespace binding corresponding to f="http://example.com/ns/f" is created, because the namespace prefix f appears only in the query prolog and is not used in an element or attribute name of the constructed node. This namespace binding does not appear in the query result, even though it is present in the statically known namespaces and is available for use during processing of the query.

Note that the following constructed element, if nested within a validate expression, cannot be validated:

<p xsi:type="xs:integer">3</p>

The constructed element will have namespace bindings for the prefixes xsi (because it is used in a name) and xml (because it is defined for every constructed element node). During validation of the constructed element, the validator will be unable to interpret the namespace prefix xs because it is has no namespace binding. Validation of this constructed element could be made possible by providing a namespace declaration attribute, as in the following example:

<p xmlns:xs="http://www.w3.org/2001/XMLSchema"
   xsi:type="xs:integer">3</p>

3.10 String Constructors

[Definition: A String Constructor creates a string from literal text and interpolated expressions. ]

The syntax of a string constructor is convenient for generating JSON, JavaScript, CSS, SPARQL, XQuery, XPath, or other languages that use curly brackets, quotation marks, or other strings that are delimiters in XQuery 3.1.

[177]    StringConstructor    ::=    "``[" StringConstructorContent "]``" /* ws: explicit */
[178]    StringConstructorContent    ::=    StringConstructorChars (StringConstructorInterpolation StringConstructorChars)* /* ws: explicit */
[179]    StringConstructorChars    ::=    (Char* - (Char* ('`{' | ']``') Char*)) /* ws: explicit */
[180]    StringConstructorInterpolation    ::=    "`{" Expr? "}`"

In a string constructor, adjacent string constructor characters are treated as literal text. Line endings are processed as elsewhere in XQuery; no other processing is performed on this text. To evaluate a string constructor, each sequence of adjacent string constructor characters is converted to a string containing the same characters, and each string constructor interpolation $i is evaluated, then converted to a string using the expression string-join($i, ' '). A string constructor interpolation that does not contain an expression (`{ }`) is ignored. The strings created from string constructor characters and the strings created from string constructor interpolations are then concatenated, in order.

For instance, the following expression:

for $s in ("one", "two", "red", "blue")
return ``[`{$s}` fish]``

evaluates to the sequence ("one fish", "two fish", "red fish", "blue fish").

Note:

Character entities are not expanded in string constructor content. Thus, ``[&lt;]`` evaluates to the string "&lt;", not the string "<".

Interpolations can contain string constructors. For instance, consider the following expression:

``[`{ $i, ``[literal text]``, $j, ``[more literal text]`` }`]``

Assuming the values $i := 1 and $j := 2, this evaluates to the string "1 literal text 2 more literal text".

The following examples are based on an example taken from the documentation of [Moustache], a JavaScript template library. Each function takes a map, containing values like these:

map {
  "name": "Chris",
  "value": 10000,
  "taxed_value": 10000 - (10000 * 0.4),
  "in_ca": true
}

This function creates a simple string.

declare function local:prize-message($a) as xs:string
{
``[Hello `{$a?name}`
You have just won `{$a?value}` dollars!
`{ 
   if ($a?in_ca) 
   then ``[Well, `{$a?taxed_value}` dollars, after taxes.]``
   else ""
}`]``
};

This is the output of the above function :

Hello Chris
You have just won 10000 dollars!
Well, 6000 dollars, after taxes.

This function creates a similar string in HTML syntax.

declare function local:prize-message($a) as xs:string
{
``[<div>
  <h1>Hello `{$a?name}`</h1>
  <p>You have just won `{$a?value}` dollars!</p>
    `{ 
      if ($a?in_ca) 
      then ``[  <p>Well, `{$a?taxed_value}` dollars, after taxes.</p> ]``
      else ""
    }`
</div>]``
};

This is the output of the above function :

<div>
  <h1>Hello Chris</h1>
  <p>You have just won 10000 dollars!</p>
  <p>Well, 6000 dollars, after taxes.</p> 
</div>

This function creates a similar string in JSON syntax.

declare function local:prize-message($a) as xs:string
{
``[{ 
  "name" : `{ $a?name }`
  "value" : `{ $a?value }`
  `{
  if ($a?in_ca) 
  then 
  ``[, 
  "taxed_value" : `{ $a?taxed_value }`]``  
  else ""
  }`
}]`` 
};

This is the output of the above function :

{ 
  "name" : "Chris",
  "value" : 10000,
  "taxed_value" : 6000
}

3.11 Maps and Arrays

Most modern programming languages have support for collections of key/value pairs, which may be called maps, dictionaries, associative arrays, hash tables, keyed lists, or objects (these are not the same thing as objects in object-oriented systems). In XQuery 3.1, we call these maps. Most modern programming languages also support ordered lists of values, which may be called arrays, vectors, or sequences. In XQuery 3.1, we have both sequences and arrays. Unlike sequences, an array is an item, and can appear as an item in a sequence.

In previous versions of the language, element structures and sequences were the only complex data structures. We are adding maps and arrays to XQuery 3.1 in order to provide lightweight data structures that are easier to optimize and less complex to use for intermediate processing and to allow programs to easily combine XML processing with JSON processing.

Note:

The XQuery 3.1 specification focuses on syntax provided for maps and arrays, especially constructors and lookup.

Some of the functionality typically needed for maps and arrays is provided by functions defined in Section 17 Maps and Arrays FO31, including functions used to read JSON to create maps and arrays, serialize maps and arrays to JSON, combine maps to create a new map, remove map entries to create a new map, iterate over the keys of a map, convert an array to create a sequence, combine arrays to form a new array, and iterate over arrays in various ways.

3.11.1 Maps

[Definition: A map is a function that associates a set of keys with values, resulting in a collection of key / value pairs.] [Definition: Each key / value pair in a map is called an entry.] [Definition: The value associated with a given key is called the associated value of the key.]

3.11.1.1 Map Constructors

A Map is created using a MapConstructor.

[170]    MapConstructor    ::=    "map" "{" (MapConstructorEntry ("," MapConstructorEntry)*)? "}"
[171]    MapConstructorEntry    ::=    MapKeyExpr ":" MapValueExpr
[172]    MapKeyExpr    ::=    ExprSingle
[173]    MapValueExpr    ::=    ExprSingle

Note:

In some circumstances, it is necessary to include whitespace before or after the colon of a MapConstructorEntry to ensure that it is parsed as intended.

For instance, consider the expression map{a:b}. Although it matches the EBNF for MapConstructor (with a matching MapKeyExpr and b matching MapValueExpr), the "longest possible match" rule requires that a:b be parsed as a QName, which results in a syntax error. Changing the expression to map{a :b} or map{a: b} will prevent this, resulting in the intended parse.

Similarly, consider these three expressions:

    map{a:b:c}
    map{a:*:c}
    map{*:b:c}

In each case, the expression matches the EBNF in two different ways, but the "longest possible match" rule forces the parse in which the MapKeyExpr is a:b, a:*, or *:b (respectively) and the MapValueExpr is c. To achieve the alternative parse (in which the MapKeyExpr is merely a or *), insert whitespace before and/or after the first colon.

See A.2 Lexical structure.

The value of the expression is a map whose entries correspond to the key-value pairs obtained by evaluating the successive MapKeyExpr and MapValueExpr expressions.

Each MapKeyExpr expression is evaluated and atomized; a type error [err:XPTY0004] occurs if the result is not a single atomic value. The associated value is the result of evaluating the corresponding MapValueExpr. If the MapValueExpr evaluates to a node, the associated value is the node itself, not a new node with the same values.

Note:

XQuery 3.1 has no operators that can distinguish a map or array from another map or array with the same values. Future versions of the XQuery Update Facility, on the other hand, will expose this difference, and need to be clear about the data model instance that is constructed.

In some existing implementations that support updates via proprietary extensions, if the MapValueExpr evaluates to a map or array, the associated value is a new map or array with the same values.

[Definition: Two atomic values K1 and K2 have the same key value if op:same-key(K1, K2) returns true, as specified in Section 17.1.1 op:same-key FO31 ] If two or more entries have the same key value then a dynamic error is raised [err:XQDY0137].

Example:

The following expression constructs a map with seven entries:

map {
  "Su" : "Sunday",
  "Mo" : "Monday",
  "Tu" : "Tuesday",
  "We" : "Wednesday",
  "Th" : "Thursday",
  "Fr" : "Friday",
  "Sa" : "Saturday"
}

Maps can nest, and can contain any XDM value. Here is an example of a nested map with values that can be string values, numeric values, or arrays:

map {
    "book": map {
        "title": "Data on the Web",
        "year": 2000,
        "author": [
            map {
                "last": "Abiteboul",
                "first": "Serge"
            },
            map {
                "last": "Buneman",
                "first": "Peter"
            },
            map {
                "last": "Suciu",
                "first": "Dan"
            }
        ],
        "publisher": "Morgan Kaufmann Publishers",
        "price": 39.95
    }
}
    
3.11.1.2 Map Lookup using Function Call Syntax

Maps are functions, and function calls can be used to look up the value associated with a key in a map. If $map is a map and $K is a key, then $map($key) is equivalent to map:get($map, $key). The semantics of such a function call are formally defined in Section 17.1.6 map:get FO31.

Examples:

Note:

XQuery 3.1 also provides an alternate syntax for map and array lookup that is more terse, supports wildcards, and allows lookup to iterate over a sequence of maps or arrays. See 3.11.3 The Lookup Operator ("?") for Maps and Arrays for details.

Map lookups can be chained.

Examples: (These examples assume that $b is bound to the books map from the previous section)

  • The expression $b("book")("title") returns the string Data on the Web.

  • The expression $b("book")("author") returns the array of authors.

  • The expression $b("book")("author")(1)("last") returns the string Abiteboul.

    (This example combines 3.11.2.2 Array Lookup using Function Call Syntax with map lookups.)

3.11.2 Arrays

3.11.2.1 Array Constructors

[Definition: An array is a function that associates a set of positions, represented as positive integer keys, with values.] The first position in an array is associated with the integer 1. [Definition: The values of an array are called its members.] In the type hierarchy, array has a distinct type, which is derived from function. Atomization converts arrays to sequences (see Atomization).

An array is created using an ArrayConstructor.

[174]    ArrayConstructor    ::=    SquareArrayConstructor | CurlyArrayConstructor
[175]    SquareArrayConstructor    ::=    "[" (ExprSingle ("," ExprSingle)*)? "]"
[176]    CurlyArrayConstructor    ::=    "array" EnclosedExpr

If a member of an array is a node, its node identity is preserved. In both forms of an ArrayConstructor, if a member expression evaluates to a node, the associated value is the node itself, not a new node with the same values. If the member expression evaluates to a map or array, the associated value is a new map or array with the same values.

A SquareArrayConstructor consists of a comma-delimited set of argument expressions. It returns an array in which each member contains the value of the corresponding argument expression.

Examples:

  • [ 1, 2, 5, 7 ] creates an array with four members: 1, 2, 5, and 7.

  • [ (), (27, 17, 0)] creates an array with two members: () and the sequence (27, 17, 0).

  • [ $x, local:items(), <tautology>It is what it is.</tautology> ] creates an array with three members: the value of $x, the result of evaluating the function call, and a tautology element.

A CurlyArrayConstructor can use any expression to create its members. It evaluates its operand expression to obtain a sequence of items and creates an array with these items as members. Unlike a SquareArrayConstructor, a comma in a CurlyArrayConstructor is the comma operator, not a delimiter.

Examples:

  • array { $x } creates an array with one member for each item in the sequence to which $x is bound.

  • array { local:items() } creates an array with one member for each item in the sequence to which local:items() evaluates.

  • array { 1, 2, 5, 7 } creates an array with four members: 1, 2, 5, and 7.

  • array { (), (27, 17, 0) } creates an array with three members: 27, 17, and 0.

  • array{ $x, local:items(), <tautology>It is what it is.</tautology> } creates an array with the following members: the items to which $x is bound, followed by the items to which local:items() evaluates, followed by a tautology element.

Note:

XQuery 3.1 does not provide explicit support for sparse arrays. Use integer-valued maps to represent sparse arrays, e.g. map { 27 : -1, 153 : 17 } .

3.11.2.2 Array Lookup using Function Call Syntax

Arrays are functions, and function calls can be used to look up the value associated with position in an array. If $array is an array and $index is an integer corresponding to a position in the array, then $array($key) is equivalent to array:get($array, $key). The semantics of such a function call are formally defined in Section 17.3.2 array:get FO31.

Examples:

  • [ 1, 2, 5, 7 ](4) evaluates to 7.

  • [ [1, 2, 3], [4, 5, 6]](2) evaluates to [4, 5, 6].

  • [ [1, 2, 3], [4, 5, 6]](2)(2) evaluates to 5.

  • [ 'a', 123, <name>Robert Johnson</name> ](3) evaluates to <name>Robert Johnson</name>.

  • array { (), (27, 17, 0) }(1) evaluates to 27.

  • array { (), (27, 17, 0) }(2) evaluates to 17.

  • array { "licorice", "ginger" }(20) raises a dynamic error [err:FOAY0001]FO31.

Note:

XQuery 3.1 also provides an alternate syntax for map and array lookup that is more terse, supports wildcards, and allows lookup to iterate over a sequence of maps or arrays. See 3.11.3 The Lookup Operator ("?") for Maps and Arrays for details.

3.11.3 The Lookup Operator ("?") for Maps and Arrays

XQuery 3.1 provides a lookup operator for maps and arrays that is more convenient for some common cases. It provides a terse syntax for simple strings as keys in maps or integers as keys in arrays, supports wildcards, and iterates over sequences of maps and arrays.

3.11.3.1 Unary Lookup
[181]    UnaryLookup    ::=    "?" KeySpecifier
[126]    KeySpecifier    ::=    NCName | IntegerLiteral | ParenthesizedExpr | "*"

Unary lookup is used in predicates (e.g. $map[?name='Mike'] or with the simple map operator (e.g. $maps ! ?name='Mike'). See 3.11.3.2 Postfix Lookup for the postfix lookup operator.

UnaryLookup returns a sequence of values selected from the context item, which must be a map or array. If the context item is not a map or an array, a type error is raised [err:XPTY0004].

If the context item is a map:

  1. If the KeySpecifier is an NCName, the UnaryLookup operator is equivalent to .(KS), where KS is the value of the NCName.

  2. If the KeySpecifier is an IntegerLiteral, the UnaryLookup operator is equivalent to .(KS), where KS is the value of the IntegerLiteral.

  3. If the KeySpecifier is a ParenthesizedExpr, the UnaryLookup operator is equivalent to the following expression, where KS is the value of the ParenthesizedExpr:

    for $k in fn:data(KS)
    return .($k)  
    
  4. If the KeySpecifier is a wildcard ("*"), the UnaryLookup operator is equivalent to the following expression:

    for $k in map:keys(.)
    return .($k)
    

    Note:

    The order of keys in map:keys() is implementation-dependent, so the order of values in the result sequence is also implementation-dependent.

If the context item is an array:

  1. If the KeySpecifier is an IntegerLiteral, the UnaryLookup operator is equivalent to .(KS), where KS is the value of the IntegerLiteral.

  2. If the KeySpecifier is an NCName, the UnaryLookup operator raises a type error [err:XPTY0004].

  3. If the KeySpecifier is a ParenthesizedExpr, the UnaryLookup operator is equivalent to the following expression, where KS is the value of the ParenthesizedExpr:

    for $k in fn:data(KS)
    return .($k)  
    
  4. If the KeySpecifier is a wildcard ("*"), the UnaryLookup operator is equivalent to the following expression:

    for $k in 1 to array:size(.)
    return .($k)
    

    Note:

    Note that array items are returned in order.

Examples:

  • ?name is equivalent to .("name"), an appropriate lookup for a map.

  • ?2 is equivalent to .(2), an appropriate lookup for an array or an integer-valued map.

  • ?("$funky / <looking @string") is equivalent to .("$funky / <looking @string"), an appropriate lookup for a map with rather odd conventions for keys.

  • ?($a) is equivalent to for $k in $a return .($k), allowing keys for an array or map to be passed using a variable.

  • ?(2 to 4) is equivalent to for $k in (2,3,4) return .($k), a convenient way to return a range of values from an array.

  • ?(3.5) raises a type error if the context item is an array because the parameter must be an integer.

  • If the context item is an array, let $x:= <node i="3"/> return ?($x/@i) does not raise a type error because the attribute is untyped.

    But let $x:= <node i="3"/> return ?($x/@i+1) does raise a type error because the + operator with an untyped operand returns a double.

  • ([1,2,3], [1,2,5], [1,2])[?3 = 5] raises an error because ?3 on one of the items in the sequence fails.

  • If $m is bound to the weekdays map described in 3.11.1 Maps, then $m?* returns the values ("Sunday","Monday","Tuesday","Wednesday", "Thursday", "Friday","Saturday"), in implementation-dependent order.

  • [1, 2, 5, 7]?* evaluates to (1, 2, 5, 7).

  • [[1, 2, 3], [4, 5, 6]]?* evaluates to ([1, 2, 3], [4, 5, 6])

3.11.3.2 Postfix Lookup
[125]    Lookup    ::=    "?" KeySpecifier

The semantics of a Postfix Lookup expression depend on the form of the KeySpecifier, as follows:

  • If the KeySpecifier is an NCName, IntegerLiteral, or Wildcard ("*"), then the expression E?S is equivalent to E!?S. (That is, the semantics of the postfix lookup operator are defined in terms of the unary lookup operator).

  • If the KeySpecifier is a ParenthesizedExpr, then the expression E?(S) is equivalent to

    for $e in E, $s in fn:data(S) return $e($s)

    Note:

    The focus for evaluating S is the same as the focus for the Lookup expression itself.

Examples:

  • map { "first" : "Jenna", "last" : "Scott" }?first evaluates to "Jenna"

  • [4, 5, 6]?2 evaluates to 5.

  • (map {"first": "Tom"}, map {"first": "Dick"}, map {"first": "Harry"})?first evaluates to the sequence ("Tom", "Dick", "Harry") .

  • ([1,2,3], [4,5,6])?2 evaluates to the sequence (2, 5).

  • ["a","b"]?3 raises a dynamic error [err:FOAY0001]FO31

3.12 FLWOR Expressions

XQuery provides a versatile expression called a FLWOR expression that may contain multiple clauses. The FLWOR expression can be used for many purposes, including iterating over sequences, joining multiple documents, and performing grouping and aggregation. The name FLWOR, pronounced "flower", is suggested by the keywords for, let, where, order by, and return, which introduce some of the clauses used in FLWOR expressions (but this is not a complete list of such clauses.)

The complete syntax of a FLWOR expression is shown here, and relevant parts of the syntax are repeated in subsequent sections of this document.

[41]    FLWORExpr    ::=    InitialClause IntermediateClause* ReturnClause
[42]    InitialClause    ::=    ForClause | LetClause | WindowClause
[43]    IntermediateClause    ::=    InitialClause | WhereClause | GroupByClause | OrderByClause | CountClause
[44]    ForClause    ::=    "for" ForBinding ("," ForBinding)*
[45]    ForBinding    ::=    "$" VarName TypeDeclaration? AllowingEmpty? PositionalVar? "in" ExprSingle
[48]    LetClause    ::=    "let" LetBinding ("," LetBinding)*
[49]    LetBinding    ::=    "$" VarName TypeDeclaration? ":=" ExprSingle
[183]    TypeDeclaration    ::=    "as" SequenceType
[46]    AllowingEmpty    ::=    "allowing" "empty"
[47]    PositionalVar    ::=    "at" "$" VarName
[50]    WindowClause    ::=    "for" (TumblingWindowClause | SlidingWindowClause)
[51]    TumblingWindowClause    ::=    "tumbling" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition WindowEndCondition?
[52]    SlidingWindowClause    ::=    "sliding" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition WindowEndCondition
[53]    WindowStartCondition    ::=    "start" WindowVars "when" ExprSingle
[54]    WindowEndCondition    ::=    "only"? "end" WindowVars "when" ExprSingle
[55]    WindowVars    ::=    ("$" CurrentItem)? PositionalVar? ("previous" "$" PreviousItem)? ("next" "$" NextItem)?
[56]    CurrentItem    ::=    EQName
[57]    PreviousItem    ::=    EQName
[58]    NextItem    ::=    EQName
[59]    CountClause    ::=    "count" "$" VarName
[60]    WhereClause    ::=    "where" ExprSingle
[61]    GroupByClause    ::=    "group" "by" GroupingSpecList
[62]    GroupingSpecList    ::=    GroupingSpec ("," GroupingSpec)*
[63]    GroupingSpec    ::=    GroupingVariable (TypeDeclaration? ":=" ExprSingle)? ("collation" URILiteral)?
[64]    GroupingVariable    ::=    "$" VarName
[65]    OrderByClause    ::=    (("order" "by") | ("stable" "order" "by")) OrderSpecList
[66]    OrderSpecList    ::=    OrderSpec ("," OrderSpec)*
[67]    OrderSpec    ::=    ExprSingle OrderModifier
[68]    OrderModifier    ::=    ("ascending" | "descending")? ("empty" ("greatest" | "least"))? ("collation" URILiteral)?
[69]    ReturnClause    ::=    "return" ExprSingle

The semantics of FLWOR expressions are based on a concept called a tuple stream. [Definition: A tuple stream is an ordered sequence of zero or more tuples.] [Definition: A tuple is a set of zero or more named variables, each of which is bound to a value that is an XDM instance.] Each tuple stream is homogeneous in the sense that all its tuples contain variables with the same names and the same static types. The following example illustrates a tuple stream consisting of four tuples, each containing three variables named $x, $y, and $z:

($x = 1003, $y = "Fred", $z = <age>21</age>)
($x = 1017, $y = "Mary", $z = <age>35</age>)
($x = 1020, $y = "Bill", $z = <age>18</age>)
($x = 1024, $y = "John", $z = <age>29</age>)

Note:

In this section, tuple streams are represented as shown in the above example. Each tuple is on a separate line and is enclosed in parentheses, and the variable bindings inside each tuple are separated by commas. This notation does not represent XQuery syntax, but is simply a representation of a tuple stream for the purpose of defining the semantics of FLWOR expressions.

Tuples and tuple streams are not part of the data model. They exist only as conceptual intermediate results during the processing of a FLWOR expression.

Conceptually, the first clause generates a tuple stream. Each clause between the first clause and the return clause takes the tuple stream generated by the previous clause as input and generates a (possibly different) tuple stream as output. The return clause takes a tuple stream as input and, for each tuple in this tuple stream, generates an XDM instance; the final result of the FLWOR expression is the ordered concatenation of these XDM instances.

The initial clause in a FLWOR expression may be a for, let, or window clause. Intermediate clauses may be for, let, window, count, where, group by, or order by clauses. These intermediate clauses may be repeated as many times as desired, in any order. The final clause of the FLWOR expression must be a return clause. The semantics of the various clauses are described in the following sections.

3.12.1 Variable Bindings

The following clauses in FLWOR expressions bind values to variables: for, let, window, count, and group by. The binding of variables for for, let, and count is governed by the following rules (the binding of variables in group by is discussed in 3.12.7 Group By Clause, the binding of variables in window clauses is discussed in 3.12.4 Window Clause):

  1. The scope of a bound variable includes all subexpressions of the containing FLWOR that appear after the variable binding. The scope does not include the expression to which the variable is bound. The following code fragment, containing two let clauses, illustrates how variable bindings may reference variables that were bound in earlier clauses, or in earlier bindings in the same clause:

    let $x := 47, $y := f($x)
    let $z := g($x, $y)
  2. A given variable may be bound more than once in a FLWOR expression, or even within one clause of a FLWOR expression. In such a case, each new binding occludes the previous one, which becomes inaccessible in the remainder of the FLWOR expression.

  3. [Definition: A variable binding may be accompanied by a type declaration, which consists of the keyword as followed by the static type of the variable, declared using the syntax in 2.5.4 SequenceType Syntax.] At run time, if the value bound to the variable does not match the declared type according to the rules for SequenceType matching, a type error is raised [err:XPTY0004]. For example, the following let clause raises a type error because the variable $salary has a type declaration that is not satisfied by the value that is bound to it:

    let $salary as xs:decimal :=  "cat"
  4. [Definition: In a for clause or window clause, when an expression is preceded by the keyword in, the value of that expression is called a binding sequence.] The for and window clauses iterate over their binding sequences, producing multiple bindings for one or more variables. Details on how binding sequences are used in for and window clauses are described in the following sections.

3.12.2 For Clause

[44]    ForClause    ::=    "for" ForBinding ("," ForBinding)*
[45]    ForBinding    ::=    "$" VarName TypeDeclaration? AllowingEmpty? PositionalVar? "in" ExprSingle
[183]    TypeDeclaration    ::=    "as" SequenceType
[46]    AllowingEmpty    ::=    "allowing" "empty"
[47]    PositionalVar    ::=    "at" "$" VarName

A for clause is used for iteration. Each variable in a for clause iterates over a sequence and is bound in turn to each item in the sequence.

If a for clause contains multiple variables, it is semantically equivalent to multiple for clauses, each containing one of the variables in the original for clause.

Example:

  • The clause

    for $x in $expr1, $y in $expr2

    is semantically equivalent to:

    for $x in $expr1
    for $y in $expr2

In the remainder of this section, we define the semantics of a for clause containing a single variable and an associated expression (following the keyword in) whose value is called the binding sequence for that variable.

If a single-variable for clause is the initial clause in a FLWOR expression, it iterates over its binding sequence, binding the variable to each item in turn. The resulting sequence of variable bindings becomes the initial tuple stream that serves as input to the next clause of the FLWOR expression. If ordering mode is ordered, the order of tuples in the tuple stream preserves the order of the binding sequence; otherwise the order of the tuple stream is implementation-dependent.

If the binding sequence contains no items, the output tuple stream depends on whether allowing empty is specified. If allowing empty is specified, the output tuple stream consists of one tuple in which the variable is bound to an empty sequence. If allowing empty is not specified, the output tuple stream consists of zero tuples.

The following examples illustrates tuple streams that are generated by initial for clauses:

  • Initial clause:

    for $x in (100, 200, 300)

    or (equivalently):

    for $x allowing empty in (100, 200, 300)

    Output tuple stream:

    ($x = 100)
    ($x = 200)
    ($x = 300)
  • Initial clause:

    for $x in ()

    Output tuple stream contains no tuples.

  • Initial clause:

    for $x allowing empty in ()

    Output tuple stream:

    ($x = ())

[Definition: A positional variable is a variable that is preceded by the keyword at.] A positional variable may be associated with a variable that is bound in a for clause. In this case, as the main variable iterates over the items in its binding sequence, the positional variable iterates over the integers that represent the ordinal numbers of these items in the binding sequence, starting with one. Each tuple in the output tuple stream contains bindings for both the main variable and the positional variable. If the binding sequence is empty and allowing empty is specified, the positional variable in the output tuple is bound to the integer zero. Positional variables always have the implied type xs:integer. The expanded QName of a positional variable must be distinct from the expanded QName of the main variable with which it is associated [err:XQST0089].

The following examples illustrate how a positional variable would have affected the results of the previous examples that generated tuples:

  • Initial clause:

    for $x at $i in (100, 200, 300)

    Output tuple stream:

    ($x = 100, $i = 1)
    ($x = 200, $i = 2)
    ($x = 300, $i = 3)
  • Initial clause:

    for $x allowing empty at $i in ()

    Output tuple stream:

    ($x = (), $i = 0)

If a single-variable for clause is an intermediate clause in a FLWOR expression, its binding sequence is evaluated for each input tuple, given the bindings in that input tuple. Each input tuple generates zero or more tuples in the output tuple stream. Each of these output tuples consists of the original variable bindings of the input tuple plus a binding of the new variable to one of the items in its binding sequence.

Note:

Although the binding sequence is conceptually evaluated independently for each input tuple, an optimized implementation may sometimes be able to avoid re-evaluating the binding sequence if it can show that the variables that the binding sequence depends on have the same values as in a previous evaluation.

For a given input tuple, if the binding sequence for the new variable in the for clause contains no items, the result depends on whether allowing empty is specified. If allowing empty is specified, the input tuple generates one output tuple, with the original variable bindings plus a binding of the new variable to an empty sequence. If allowing empty is not specified, the input tuple generates zero output tuples (it is not represented in the output tuple stream.)

If the new variable introduced by a for clause has an associated positional variable, the output tuples generated by the for clause also contain bindings for the positional variable. In this case, as the new variable is bound to each item in its binding sequence, the positional variable is bound to the ordinal position of that item within the binding sequence, starting with one. Note that, since the positional variable represents a position within a binding sequence, the output tuples corresponding to each input tuple are independently numbered, starting with one. For a given input tuple, if the binding sequence is empty and allowing empty is specified, the positional variable in the output tuple is bound to the integer zero.

If ordering mode is ordered, the tuples in the output tuple stream are ordered primarily by the order of the input tuples from which they are derived, and secondarily by the order of the binding sequence for the new variable; otherwise the order of the output tuple stream is implementation-dependent.

The following examples illustrates the effects of intermediate for clauses:

  • Input tuple stream:

    ($x = 1)
    ($x = 2)
    ($x = 3)
    ($x = 4)

    Intermediate for clause:

    for $y in ($x to 3)

    Output tuple stream (assuming ordering mode is ordered):

    ($x = 1, $y = 1)
    ($x = 1, $y = 2)
    ($x = 1, $y = 3)
    ($x = 2, $y = 2)
    ($x = 2, $y = 3)
    ($x = 3, $y = 3)
    

    Note:

    In this example, there is no output tuple that corresponds to the input tuple ($x = 4) because, when the for clause is evaluated with the bindings in this input tuple, the resulting binding sequence for $y is empty.

  • This example shows how the previous example would have been affected by a positional variable (assuming the same input tuple stream):

    for $y at $j in ($x to 3)

    Output tuple stream (assuming ordering mode is ordered):

    ($x = 1, $y = 1, $j = 1)
    ($x = 1, $y = 2, $j = 2)
    ($x = 1, $y = 3, $j = 3)
    ($x = 2, $y = 2, $j = 1)
    ($x = 2, $y = 3, $j = 2)
    ($x = 3, $y = 3, $j = 1)
    
  • This example shows how the previous example would have been affected by allowing empty. Note that allowing empty causes the input tuple ($x = 4) to be represented in the output tuple stream, even though the binding sequence for $y contains no items for this input tuple. This example illustrates that allowing empty in a for clause serves a purpose similar to that of an "outer join" in a relational database query. (Assume the same input tuple stream as in the previous example.)

    for $y allowing empty at $j in ($x to 3)

    Output tuple stream (assuming ordering mode is ordered):

    ($x = 1, $y = 1, $j = 1)
    ($x = 1, $y = 2, $j = 2)
    ($x = 1, $y = 3, $j = 3)
    ($x = 2, $y = 2, $j = 1)
    ($x = 2, $y = 3, $j = 2)
    ($x = 3, $y = 3, $j = 1)
    ($x = 4, $y = (), $j = 0)
    
  • This example shows how a for clause that binds two variables is semantically equivalent to two for clauses that bind one variable each. We assume that this for clause occurs at the beginning of a FLWOR expression. It is equivalent to an initial single-variable for clause that provides an input tuple stream to an intermediate single-variable for clause.

    for $x in (1, 2, 3, 4), $y in ($x to 3)

    Output tuple stream (assuming ordering mode is ordered):

    ($x = 1, $y = 1)
    ($x = 1, $y = 2)
    ($x = 1, $y = 3)
    ($x = 2, $y = 2)
    ($x = 2, $y = 3)
    ($x = 3, $y = 3)
    

In the above examples, if ordering mode had been unordered, the output tuple streams would have consisted of the same tuples, with the same values for the positional variables, but the ordering of the tuples would have been implementation-dependent.

A for clause may contain one or more type declarations, identified by the keyword as. The semantics of type declarations are defined in 3.12.1 Variable Bindings.

3.12.3 Let Clause

[48]    LetClause    ::=    "let" LetBinding ("," LetBinding)*
[49]    LetBinding    ::=    "$" VarName TypeDeclaration? ":=" ExprSingle
[183]    TypeDeclaration    ::=    "as" SequenceType

The purpose of a let clause is to bind values to one or more variables. Each variable is bound to the result of evaluating an expression.

If a let clause contains multiple variables, it is semantically equivalent to multiple let clauses, each containing a single variable. For example, the clause

let $x := $expr1, $y := $expr2

is semantically equivalent to the following sequence of clauses:

let $x := $expr1
let $y := $expr2

In the remainder of this section, we define the semantics of a let clause containing a single variable V and an associated expression E.

If a single-variable let clause is the initial clause in a FLWOR expression, it simply binds the variable V to the result of the expression E. The result of the let clause is a tuple stream consisting of one tuple with a single binding that binds V to the result of E. This tuple stream serves as input to the next clause in the FLWOR expression.

If a single-variable let clause is an intermediate clause in a FLWOR expression, it adds a new binding for variable V to each tuple in the input tuple stream. For each input tuple, the value bound to V is the result of evaluating expression E, given the bindings that are already present in that input tuple. The resulting tuples become the output tuple stream of the let clause.

The number of tuples in the output tuple stream of an intermediate let clause is the same as the number of tuples in the input tuple stream. The number of bindings in the output tuples is one more than the number of bindings in the input tuples, unless the input tuples already contain bindings for V; in this case, the new binding for V occludes (replaces) the earlier binding for V, and the number of bindings is unchanged.

A let clause may contain one or more type declarations, identified by the keyword as. The semantics of type declarations are defined in 3.12.1 Variable Bindings.

The following code fragment illustrates how a for clause and a let clause can be used together. The for clause produces an initial tuple stream containing a binding for variable $d to each department number found in a given input document. The let clause adds an additional binding to each tuple, binding variable $e to a sequence of employees whose department number matches the value of $d in that tuple.

for $d in fn:doc("depts.xml")/depts/deptno
let $e := fn:doc("emps.xml")/emps/emp[deptno eq $d]

3.12.4 Window Clause

[50]    WindowClause    ::=    "for" (TumblingWindowClause | SlidingWindowClause)
[51]    TumblingWindowClause    ::=    "tumbling" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition WindowEndCondition?
[52]    SlidingWindowClause    ::=    "sliding" "window" "$" VarName TypeDeclaration? "in" ExprSingle WindowStartCondition WindowEndCondition
[53]    WindowStartCondition    ::=    "start" WindowVars "when" ExprSingle
[54]    WindowEndCondition    ::=    "only"? "end" WindowVars "when" ExprSingle
[55]    WindowVars    ::=    ("$" CurrentItem)? PositionalVar? ("previous" "$" PreviousItem)? ("next" "$" NextItem)?
[56]    CurrentItem    ::=    EQName
[47]    PositionalVar    ::=    "at" "$" VarName
[57]    PreviousItem    ::=    EQName
[58]    NextItem    ::=    EQName

Like a for clause, a window clause iterates over its binding sequence and generates a sequence of tuples. In the case of a window clause, each tuple represents a window. [Definition: A window is a sequence of consecutive items drawn from the binding sequence.] Each window is represented by at least one and at most nine bound variables. The variables have user-specified names, but their roles are as follows:

  • Window-variable: Bound to the sequence of items from the binding sequence that comprise the window.

  • Start-item: (Optional) Bound to the first item in the window.

  • Start-item-position: (Optional) Bound to the ordinal position of the first window item in the binding sequence. Start-item-position is a positional variable; hence, its type is xs:integer

  • Start-previous-item: (Optional) Bound to the item in the binding sequence that precedes the first item in the window (empty sequence if none).

  • Start-next-item: (Optional) Bound to the item in the binding sequence that follows the first item in the window (empty sequence if none).

  • End-item: (Optional) Bound to the last item in the window.

  • End-item-position: (Optional) Bound to the ordinal position of the last window item in the binding sequence. End-item-position is a positional variable; hence, its type is xs:integer

  • End-previous-item: (Optional) Bound to the item in the binding sequence that precedes the last item in the window (empty sequence if none).

  • End-next-item: (Optional) Bound to the item in the binding sequence that follows the last item in the window (empty sequence if none).

All variables in a window clause must have distinct names; otherwise a static error is raised [err:XQST0103].

The following is an example of a window clause that binds nine variables to the roles listed above. In this example, the variables are named $w, $s, $spos, $sprev, $snext, $e, $epos, $eprev, and $enext respectively. A window clause always binds the window variable, but typically binds only a subset of the other variables.

for tumbling window $w in (2, 4, 6, 8, 10)
    start $s at $spos previous $sprev next $snext when true() 
    end $e at $epos previous $eprev next $enext when true()

Windows are created by iterating over the items in the binding sequence, in order, identifying the start item and the end item of each window by evaluating the WindowStartCondition and the WindowEndCondition. Each of these conditions is satisfied if the effective boolean value of the expression following the when keyword is true. The start item of the window is an item that satisfies the WindowStartCondition (see 3.12.4.1 Tumbling Windows and 3.12.4.2 Sliding Windows for a more complete explanation.) The end item of the window is the first item in the binding sequence, beginning with the start item, that satisfies the WindowEndCondition (again, see 3.12.4.1 Tumbling Windows and 3.12.4.2 Sliding Windows for more details.) Each window contains its start item, its end item, and all items that occur between them in the binding sequence. If the end item is the start item, then the window contains only one item. If a start item is identified, but no following item in the binding sequence satisfies the WindowEndCondition, then the only keyword determines whether a window is generated: if only end is specified, then no window is generated; otherwise, the end item is set to the last item in the binding sequence and a window is generated.

In the above example, the WindowStartCondition and WindowEndCondition are both true, which causes each item in the binding sequence to be in a separate window. Typically, the WindowStartCondition and WindowEndCondition are expressed in terms of bound variables. For example, the following WindowStartCondition might be used to start a new window for every item in the binding sequence that is larger than both the previous item and the following item:

start $s previous $sprev next $snext
   when $s > $sprev and $s > $snext

The scoping rules for the variables bound by a window clause are as follows:

  • In the when-expression of the WindowStartCondition, the following variables (identified here by their roles) are in scope (if bound): start-item, start-item-position, start-previous-item, start-next-item.

  • In the when-expression of the WindowEndCondition, the following variables (identified here by their roles) are in scope (if bound): start-item, start-item-position, start-previous-item, start-next-item, end-item, end-item-position, end-previous-item, end-next-item.

  • In the clauses of the FLWOR expression that follow the window clause, all nine of the variables bound by the window clause (including window-variable) are in scope (if bound).

In a window clause, the keyword tumbling or sliding determines the way in which the starting item of each window is identified, as explained in the following sections.

3.12.4.1 Tumbling Windows

If the window type is tumbling, then windows never overlap. The search for the start of the first window begins at the beginning of the binding sequence. After each window is generated, the search for the start of the next window begins with the item in the binding sequence that occurs after the ending item of the last generated window. Thus, no item that occurs in one window can occur in another window drawn from the same binding sequence (unless the sequence contains the same item more than once). In a tumbling window clause, the end clause is optional; if it is omitted, the start clause is applied to identify all potential starting items in the binding sequence, and a window is constructed for each starting item, including all items from that starting item up to the item before the next window's starting item, or the end of the binding sequence, whichever comes first.

The following examples illustrate the use of tumbling windows.

  • Show non-overlapping windows of three items.

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
        start at $s when fn:true()
        only end at $e when $e - $s eq 2
    return <window>{ $w }</window>

    Result of the above query:

    <window>2 4 6</window>
    <window>8 10 12</window>
  • Show averages of non-overlapping three-item windows.

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
        start at $s when fn:true()
        only end at $e when $e - $s eq 2
    return avg($w)

    Result of the above query:

    4 10
  • Show first and last items in each window of three items.

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
        start $first at $s when fn:true()
        only end $last at $e when $e - $s eq 2
    return <window>{ $first, $last }</window>

    Result of the above query:

    <window>2 6</window>
    <window>8 12</window>
  • Show non-overlapping windows of up to three items (illustrates end clause without the only keyword).

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
        start at $s when fn:true()
        end at $e when $e - $s eq 2
    return <window>{ $w }</window>

    Result of the above query:

    <window>2 4 6</window>
    <window>8 10 12</window>
    <window>14</window>
  • Show non-overlapping windows of up to three items (illustrates use of start without explicit end).

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
        start at $s when $s mod 3 = 1
    return <window>{ $w }</window>

    Result of the above query:

    <window>2 4 6</window>
    <window>8 10 12</window>
    <window>14</window>
  • Show non-overlapping sequences starting with a number divisible by 3.

    for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
        start $first when $first mod 3 = 0
    return <window>{ $w }</window>

    Result of the above query:

    <window>6 8 10</window>
    <window>12 14</window>
3.12.4.2 Sliding Windows

If the window type is sliding window, then windows may overlap. Every item in the binding sequence that satisfies the WindowStartCondition is the starting item of a new window. Thus, a given item may be found in multiple windows drawn from the same binding sequence.

The following examples illustrate the use of sliding windows.

  • Show windows of three items.

    for sliding window $w in (2, 4, 6, 8, 10, 12, 14)
        start at $s when fn:true()
        only end at $e when $e - $s eq 2
    return <window>{ $w }</window>

    Result of the above query:

    <window>2 4 6</window>
    <window>4 6 8</window>
    <window>6 8 10</window>
    <window>8 10 12</window>
    <window>10 12 14</window>
  • Show moving averages of three items.

    for sliding window $w in (2, 4, 6, 8, 10, 12, 14)
        start at $s when fn:true()
        only end at $e when $e - $s eq 2
    return avg($w)

    Result of the above query:

    4 6 8 10 12
  • Show overlapping windows of up to three items (illustrates end clause without the only keyword).

    for sliding window $w in (2, 4, 6, 8, 10, 12, 14)
        start at $s when fn:true()
        end at $e when $e - $s eq 2
    return <window>{ $w }</window>

    Result of the above query:

    <window>2 4 6</window>
    <window>4 6 8</window>
    <window>6 8 10</window>
    <window>8 10 12</window>
    <window>10 12 14</window>
    <window>12 14</window>
    <window>14</window>
3.12.4.3 Effects of Window Clauses on the Tuple Stream

The effects of a window clause on the tuple stream are similar to the effects of a for clause. As described in 3.12.4 Window Clause, a window clause generates zero or more windows, each of which is represented by at least one and at most nine bound variables.

If the window clause is the initial clause in a FLWOR expression, the bound variables that describe each window become an output tuple. These tuples form the initial tuple stream that serves as input to the next clause of the FLWOR expression. If ordering mode is ordered, the order of tuples in the tuple stream is the order in which their start items appear in the binding sequence; otherwise the order of the tuple stream is implementation-dependent. The cardinality of the tuple stream is equal to the number of windows.

If a window clause is an intermediate clause in a FLWOR expression, each input tuple generates zero or more output tuples, each consisting of the original bound variables of the input tuple plus the new bound variables that represent one of the generated windows. For each tuple T in the input tuple stream, the output tuple stream will contain NT tuples, where NT is the number of windows generated by the window clause, given the bindings in the input tuple T. Input tuples for which no windows are generated are not represented in the output tuple stream. If ordering mode is ordered, the order of tuples in the output stream is determined primarily by the order of the input tuples from which they were derived, and secondarily by the order in which their start items appear in the binding sequence. If ordering mode is unordered, the order of tuples in the output stream is implementation-dependent.

The following example illustrates a window clause that is the initial clause in a FLWOR expression. The example is based on input data that consists of a sequence of closing stock prices for a specific company. For this example we assume the following input data (assume that the price elements have a validated type of xs:decimal):

<stock>
  <closing> <date>2008-01-01</date> <price>105</price> </closing>
  <closing> <date>2008-01-02</date> <price>101</price> </closing>
  <closing> <date>2008-01-03</date> <price>102</price> </closing>
  <closing> <date>2008-01-04</date> <price>103</price> </closing>
  <closing> <date>2008-01-05</date> <price>102</price> </closing>
  <closing> <date>2008-01-06</date> <price>104</price> </closing>
</stock>

A user wishes to find "run-ups," which are defined as sequences of dates that begin with a "low" and end with a "high" price (that is, the stock price begins to rise on the first day of the run-up, and continues to rise or remain even through the last day of the run-up.) The following query uses a tumbling window to find run-ups in the input data:

for tumbling window $w in //closing
   start $first next $second when $first/price < $second/price
   end $last next $beyond when $last/price > $beyond/price
return
   <run-up>
      <start-date>{fn:data($first/date)}</start-date>
      <start-price>{fn:data($first/price)}</start-price>
      <end-date>{fn:data($last/date)}</end-date>
      <end-price>{fn:data($last/price)}</end-price>
   </run-up>

For our sample input data, this tumbling window clause generates a tuple stream consisting of two tuples, each representing a window and containing five bound variables named $w, $first, $second, $last, and $beyond. The return clause is evaluated for each of these tuples, generating the following query result:

<run-up>
   <start-date>2008-01-02</start-date>
   <start-price>101</start-price>
   <end-date>2008-01-04</end-date>
   <end-price>103</end-price>
</run-up>
<run-up>
   <start-date>2008-01-05</start-date>
   <start-price>102</start-price>
   <end-date>2008-01-06</end-date>
   <end-price>104</end-price>
</run-up>

The following example illustrates a window clause that is an intermediate clause in a FLWOR expression. In this example, the input data contains closing stock prices for several different companies, each identified by a three-letter symbol. We assume the following input data (again assuming that the type of the price element is xs:decimal):

<stocks>
  <closing> <symbol>ABC</symbol> <date>2008-01-01</date> <price>105</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-01</date> <price>057</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-02</date> <price>101</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-02</date> <price>054</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-03</date> <price>102</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-03</date> <price>056</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-04</date> <price>103</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-04</date> <price>052</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-05</date> <price>101</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-05</date> <price>055</price> </closing>
  <closing> <symbol>ABC</symbol> <date>2008-01-06</date> <price>104</price> </closing>
  <closing> <symbol>DEF</symbol> <date>2008-01-06</date> <price>059</price> </closing>
</stocks>

As in the previous example, we want to find "run-ups," which are defined as sequences of dates that begin with a "low" and end with a "high" price for a specific company. In this example, however, the input data consists of stock prices for multiple companies. Therefore it is necessary to isolate the stock prices of each company before forming windows. This can be accomplished by an initial for and let clause, followed by a window clause, as follows:

for $symbol in fn:distinct-values(//symbol)
let $closings := //closing[symbol = $symbol]
for tumbling window $w in $closings
   start $first next $second when $first/price < $second/price
   end $last next $beyond when $last/price > $beyond/price
return
   <run-up symbol="{$symbol}">
      <start-date>{fn:data($first/date)}</start-date>
      <start-price>{fn:data($first/price)}</start-price>
      <end-date>{fn:data($last/date)}</end-date>
      <end-price>{fn:data($last/price)}</end-price>
   </run-up>

Note:

In the above example, the for and let clauses could be rewritten as follows:

for $closings in //closing
let $symbol := $closings/symbol
group by $symbol

The group by clause is described in 3.12.7 Group By Clause.

The for and let clauses in this query generate an initial tuple stream consisting of two tuples. In the first tuple, $symbol is bound to "ABC" and $closings is bound to the sequence of closing elements for company ABC. In the second tuple, $symbol is bound to "DEF" and $closings is bound to the sequence of closing elements for company DEF.

The window clause operates on this initial tuple stream, generating two windows for the first tuple and two windows for the second tuple. The result is a tuple stream consisting of four tuples, each with the following bound variables: $symbol, $closings, $w, $first, $second, $last, and $beyond. The return clause is then evaluated for each of these tuples, generating the following query result:

<run-up symbol="ABC">
   <start-date>2008-01-02</start-date>
   <start-price>101</start-price>
   <end-date>2008-01-04</end-date>
   <end-price>103</end-price>
</run-up>
<run-up symbol="ABC">
   <start-date>2008-01-05</start-date>
   <start-price>101</start-price>
   <end-date>2008-01-06</end-date>
   <end-price>104</end-price>
</run-up>
<run-up symbol="DEF">
   <start-date>2008-01-02</start-date>
   <start-price>054</start-price>
   <end-date>2008-01-03</end-date>
   <end-price>056</end-price>
</run-up>
<run-up symbol="DEF">
   <start-date>2008-01-04</start-date>
   <start-price>052</start-price>
   <end-date>2008-01-06</end-date>
   <end-price>059</end-price>
</run-up>

3.12.5 Where Clause

[60]    WhereClause    ::=    "where" ExprSingle

A where clause serves as a filter for the tuples in its input tuple stream. 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 in the output tuple stream; otherwise the tuple is discarded.

Examples:

  • This example illustrates the effect of a where clause on a tuple stream:

    Input tuple stream:

    ($a = 5, $b = 11)
    ($a = 91, $b = 42)
    ($a = 17, $b = 30)
    ($a = 85, $b = 63)

    where clause:

    where $a > $b

    Output tuple stream:

    ($a = 91, $b = 42)
    ($a = 85, $b = 63)
  • The following query illustrates how a where clause might be used with a positional variable to perform sampling on an input sequence. The query returns one value out of each one hundred input values.

    for $x at $i in $inputvalues
    where $i mod 100 = 0
    return $x

3.12.6 Count Clause

[59]    CountClause    ::=    "count" "$" VarName

The purpose of a count clause is to enhance the tuple stream with a new variable that is bound, in each tuple, to the ordinal position of that tuple in the tuple stream. The name of the new variable is specified in the count clause.

The output tuple stream of a count clause is the same as its input tuple stream, with each tuple enhanced by one additional variable that is bound to the ordinal position of that tuple in the tuple stream. However, if the name of the new variable is the same as the name of an existing variable in the input tuple stream, the new variable occludes (replaces) the existing variable of the same name, and the number of bound variables in each tuple is unchanged.

The following examples illustrate uses of the count clause:

  • This example illustrates the effect of a count clause on an input tuple stream:

    Input tuple stream:

    ($name = "Bob", $age = 21)
    ($name = "Carol", $age = 19)
    ($name = "Ted", $age = 20)
    ($name = "Alice", $age = 22)

    count clause:

    count $counter

    Output tuple stream:

    ($name = "Bob", $age = 21, $counter = 1)
    ($name = "Carol", $age = 19, $counter = 2)
    ($name = "Ted", $age = 20, $counter = 3)
    ($name = "Alice", $age = 22, $counter = 4)
  • This example illustrates how a counter might be used to filter the result of a query. The query ranks products in order by decreasing sales, and returns the three products with the highest sales. Assume that the variable $products is bound to a sequence of product elements, each of which has name and sales child-elements.

    for $p in $products
    order by $p/sales descending
    count $rank
    where $rank <= 3
    return
       <product rank="{$rank}">
          {$p/name, $p/sales}
       </product>

    The result of this query has the following structure:

    <product rank="1">
       <name>Toaster</name>
       <sales>968</sales>
    </product>
    <product rank="2">
       <name>Blender</name>
       <sales>520</sales>
    </product>
    <product rank="3">
       <name>Can Opener</name>
       <sales>475</sales>
    </product>

3.12.7 Group By Clause

[61]    GroupByClause    ::=    "group" "by" GroupingSpecList
[62]    GroupingSpecList    ::=    GroupingSpec ("," GroupingSpec)*
[63]    GroupingSpec    ::=    GroupingVariable (TypeDeclaration? ":=" ExprSingle)? ("collation" URILiteral)?
[64]    GroupingVariable    ::=    "$" VarName

A group by clause generates an output tuple stream in which each tuple represents a group of tuples from the input tuple stream that have equivalent grouping keys. We will refer to the tuples in the input tuple stream as pre-grouping tuples, and the tuples in the output tuple stream as post-grouping tuples.

The group by clause assigns each pre-grouping tuple to a group, and generates one post-grouping tuple for each group. In the post-grouping tuple for a group, each grouping key is represented by a variable that was specified in a GroupingSpec, and every variable that appears in the pre-grouping tuples that were assigned to that group is represented by a variable of the same name, bound to a sequence of all values bound to the variable in any of these pre-grouping tuples. Subsequent clauses in the FLWOR expression see only the variable bindings in the post-grouping tuples; they no longer have access to the variable bindings in the pre-grouping tuples. The number of post-grouping tuples is less than or equal to the number of pre-grouping tuples.

A group by clause contains one or more grouping specifications, as shown in the grammar. [Definition: Each grouping specification specifies one grouping variable, which refers to variable bindings in the pre-grouping tuples. The values of the grouping variables are used to assign pre-grouping tuples to groups.] Each grouping specification may optionally provide an expression to which its grouping variable is bound. If no expression is provided, the grouping variable name must be equal (by the eq operator on expanded QNames) to the name of a variable in the input tuple stream, and it refers to that variable; otherwise a static error is raised [err:XQST0094]. For each grouping specification that contains a binding expression, a let binding is created in the pre-grouping tuples, and the grouping variable refers to that let binding. For example, the clause:

group by $g1, $g2 := $expr1, $g3 := $expr2 collation "Spanish"

is semantically equivalent to the following sequence of clauses:

let $g2 := $expr1
let $g3 := $expr2
group by $g1, $g2, $g3 collation "Spanish"

The process of group formation proceeds as follows:

  1. [Definition: The atomized value of a grouping variable is called a grouping key.] For each pre-grouping tuple, the grouping keys are created by atomizing the values of the grouping variables (in the post-grouping tuples, each grouping variable is set to the value of the corresponding grouping key, as discussed below). If the value of any grouping variable consists of more than one item, a type error is raised [err:XPTY0004]. If a type declaration is present and the resulting atomized value is not an instance of the specified type, a type error is raised [err:XPTY0004].

  2. The input tuple stream is partitioned into groups of tuples whose grouping keys are equivalent. [Definition: Two tuples T1 and T2 have equivalent grouping keys if and only if, for each grouping variable GV, the atomized value of GV in T1 is deep-equal to the atomized value of GV in T2, as defined by applying the function fn:deep-equal using the appropriate collation.] If these values are of different numeric types, and differ from each other by small amounts, then the deep-equal relationship is not transitive, because of rounding effects occurring during type promotion. When comparing three values A, B, and C such that A eq B, B eq C, but A ne C, then the number of items in the result of the function (as well as the choice of which items are returned) is implementation-dependent, subject only to the constraints that (a) no two items in the result sequence compare equal to each other, and (b) every input item that does not appear in the result sequence compares equal to some item that does appear in the result sequence. See Section 14.2.1 fn:distinct-values FO31 for further discussion of this issue in a different context.

    Note:

    The atomized grouping key will always be either an empty sequence or a single atomic value. Defining equivalence by reference to the fn:deep-equal function ensures that the empty sequence is equivalent only to the empty sequence, that NaN is equivalent to NaN, that untypedAtomic values are compared as strings, and that values for which the eq operator is not defined are considered non-equivalent.

  3. The appropriate collation for comparing two grouping keys is the collation specified in the pertinent GroupingSpec if present, or the default collation from the static context otherwise. If the collation is specified by a relative URI, that relative URI is resolved to an absolute URI using the Static Base URI. If the specified collation is not found in statically known collations, a static error is raised [err:XQST0076].

Each group of tuples produced by the above process results in one post-grouping tuple. The pre-grouping tuples from which the group is derived have equivalent grouping keys, but these keys are not necessarily identical (for example, the strings "Frog" and "frog" might be equivalent according to the collation in use.) In the post-grouping tuple, each grouping variable is bound to the value of the corresponding grouping key.

In the post-grouping tuple generated for a given group, each non-grouping variable is bound to a sequence containing the concatenated values of that variable in all the pre-grouping tuples that were assigned to that group. If ordering mode is ordered, the values derived from individual tuples are concatenated in a way that preserves the order of the pre-grouping tuple stream; otherwise the ordering of these values is implementation-dependent.

Note:

This behavior may be surprising to SQL programmers, since SQL reduces the equivalent of a non-grouping variable to one representative value. Consider the following query:

let $x := 64000
for $c in //customer
where $c/salary > $x
group by $d := $c/department
return
<department name="{$d}">
   Number of employees earning more than ${$x} is {count($c)}
</department>

If there are three qualifying customers in the sales department this evaluates to:


<department name="sales">
  Number of employees earning more than $64000 64000 64000 is 3
</department>

In XQuery, each group is a sequence of items that match the group by criteria—in a tree-structured language like XQuery, this is convenient, because further structures can be built based on the items in this sequence. Because there are three items in the group, $x evaluates to a sequence of three items. To reduce this to one item, use fn:distinct-values():

let $x := 64000
for $c in //customer
let $d := $c/department
where $c/salary > $x
group by $d
return
 <department name="{$d}">
  Number of employees earning more than ${distinct-values($x)} is {count($c)}
 </department>

Note:

In general, the static type of a variable in a post-grouping tuple is different from the static type of the variable with the same name in the pre-grouping tuples.

The order in which tuples appear in the post-grouping tuple stream is implementation-dependent.

Note:

An order by clause can be used to impose a value-based ordering on the post-grouping tuple stream. Similarly, if it is desired to impose a value-based ordering within a group (i.e., on the sequence of items bound to a non-grouping variable), this can be accomplished by a nested FLWOR expression that iterates over these items and applies an order by clause. In some cases, a value-based ordering within groups can be accomplished by applying an order by clause on a non-grouping variable before applying the group by clause.

A group by clause rebinds all the variables in the input tuple stream. The scopes of these variables are not affected by the group by clause, but in post-grouping tuples the values of the variables represent group properties rather than properties of individual pre-grouping tuples.

Examples:

  • This example illustrates the effect of a group by clause on a tuple stream.

    Input tuple stream:

    ($storeno = <storeno>S101</storeno>, $itemno = <itemno>P78395</itemno>)
    ($storeno = <storeno>S102</storeno>, $itemno = <itemno>P94738</itemno>)
    ($storeno = <storeno>S101</storeno>, $itemno = <itemno>P41653</itemno>)
    ($storeno = <storeno>S102</storeno>, $itemno = <itemno>P70421</itemno>)
    

    group by clause:

    group by $storeno

    Output tuple stream:

    ($storeno = S101, $itemno = (<itemno>P78395</itemno>, <itemno>P41653</itemno>))
    ($storeno = S102, $itemno = (<itemno>P94738</itemno>, <itemno>P70421</itemno>))
  • This example and the ones that follow are based on two separate sequences of elements, named $sales and $products. We assume that the variable $sales is bound to a sequence of elements with the following structure:

    <sales>
       <storeno>S101</storeno>
       <itemno>P78395</itemno>
       <qty>125</qty>
    </sales>

    We also assume that the variable $products is bound to a sequence of elements with the following structure:

    <product>
       <itemno>P78395</itemno>
       <price>25.00</price>
       <category>Men's Wear</category>
    </product>

    The simplest kind of grouping query has a single grouping variable. The query in this example finds the total quantity of items sold by each store:

    for $s in $sales
    let $storeno := $s/storeno
    group by $storeno
    return <store number="{$storeno}" total-qty="{sum($s/qty)}"/>

    The result of this query is a sequence of elements with the following structure:

    <store number="S101" total-qty="1550" />
    <store number="S102" total-qty="2125" />
  • In a more realistic example, a user might be interested in the total revenue generated by each store for each product category. Revenue depends on both the quantity sold of various items and the price of each item. The following query joins the two input sequences and groups the resulting tuples by two grouping variables:

    for $s in $sales,
        $p in $products[itemno = $s/itemno]
    let $revenue := $s/qty * $p/price
    group by $storeno := $s/storeno, 
        $category := $p/category
    return
        <summary storeno="{$storeno}"
                  category="{$category}"
                  revenue="{sum($revenue)}"/>
    

    The result of this query is a sequence of elements with the following structure:

    <summary storeno="S101" category="Men's Wear" revenue="10185"/>
    <summary storeno="S101" category="Stationery" revenue="4520"/>
    <summary storeno="S102" category="Men's Wear" revenue="9750"/>
    <summary storeno="S102" category="Appliances" revenue="22650"/>
    <summary storeno="S102" category="Jewelry" revenue="30750"/>
  • The result of the previous example was a "flat" list of elements. A user might prefer the query result to be presented in the form of a hierarchical report, grouped primarily by store (in order by store number) and secondarily by product category. Within each store, the user might want to see only those product categories whose total revenue exceeds $10,000, presented in descending order by their total revenue. This report is generated by the following query:

    for $s1 in $sales
    let $storeno := $s1/storeno
    group by $storeno
    order by $storeno
    return
      <store storeno="{$storeno}">
        {for $s2 in $s1,
             $p in $products[itemno = $s2/itemno]
         let $category := $p/category,
             $revenue := $s2/qty * $p/price
         group by $category
         let $group-revenue := sum($revenue)
         where $group-revenue > 10000
         order by $group-revenue descending
         return <category name="{$category}" revenue="{$group-revenue}"/>
        }
      </store>
    

    The result of this example query has the following structure:

    <store storeno="S101">
       <category name="Men's Wear" revenue="10185"/>
    </store>
    <store storeno="S102">
       <category name="Jewelry" revenue="30750"/>
       <category name="Appliances" revenue="22650"/>
    </store>
  • The following example illustrates how to avoid a possible pitfall in writing grouping queries.

    In each post-grouping tuple, all variables except for the grouping variable are bound to sequences of items derived from all the pre-grouping tuples from which the group was formed. For instance, in the following query, $high-price is bound to a sequence of items in the post-grouping tuple.

    let $high-price := 1000
    for $p in $products[price > $high-price]
    let $category := $p/category
    group by $category
    return
       <category name="{$category}">
          {fn:count($p)} products have price greater than {$high-price}.
       </category>

    If three products in the "Men's Wear" category have prices greater than 1000, the result of this query might look (in part) like this:

    <category name="Men's Wear">
       3 products have price greater than 1000 1000 1000.
    </category>

    The repetition of "1000" in this query result is due to the fact that $high-price is not a grouping variable. One way to avoid this repetition is to move the binding of $high-price to an outer-level FLWOR expression, as follows:

    let $high-price := 1000
    return
       for $p in $products[price > $high-price]
       let $category := $p/category
       group by $category
       return
          <category name="{$category}">
             {fn:count($p)} products have price greater than {$high-price}.
          </category>

    The result of the revised query might contain the following element:

    <category name="Men's Wear">
       3 products have price greater than 1000.
    </category>

3.12.8 Order By Clause

[65]    OrderByClause    ::=    (("order" "by") | ("stable" "order" "by")) OrderSpecList
[66]    OrderSpecList    ::=