XQuery 1.0 and XPath 2.0 Functions and Operators

1.1 Function Overloading

In general, the specifications named above do not support function overloading. Consequently, there are no overloaded functions in this document except for legacy [XPath 1.0] functions such as fn:string(), which accepts a single argument of a variety of types, and concat() which accepts a variable number of xs:string arguments. In addition, the functions defined in 6 Functions and Operators on Numerics that accept numeric arguments accept arguments of type xs:integer, xs:decimal, xs:float or xs:double. See 1.2 Function Signatures and Descriptions. Operators such as "+" may be overloaded.

1.2 Function Signatures and Descriptions

Each function is defined by specifying its signature, a description of the return type and each of the parameters and its semantics. For many functions, examples are included to illustrate their use.

Each function's signature is presented in a form like this:

In this notation, function-name, in bold-face, is the name of the function whose signature is being specified. If the function takes no parameters, then the name is followed by an empty set of parentheses: "()"; otherwise, the name is followed by a parenthesized list of parameter declarations, each declaration specifying the static type of the parameter, in italics, and a non-normative name used to describe the function's semantics. If there are two or more parameter declarations, they are separated by a comma. The return-type, also in italics, specifies the static type of the value returned by the function. In most cases, the dynamic type returned by the function is the same as its static type. The types "node" and "item" are indicated in function signatures as "node()" and "item()" repectively.

In some cases the word "numeric" is used in function signatures as a shorthand to indicate the four numeric types: xs:integer, xs:decimal, xs:float and xs:double. For example, a function with the signature

For most functions there is a initial paragraph describing what the function does followed by semantic rules. These rules are meant to be followed in the order that they appear in this document.

In some cases, the dynamic type returned by a function depends on the type(s) of its argument(s). These special functions are indicated by using bold italics for the return type. The semantic rules specifying the type of the value returned are documented in the function definition. The rules are described more formally in Section 6.2 Standard functions with specific typing rules^FS.

The function name is a QName as defined in [XML Schema Part 2: Datatypes] and must adhere to its syntactic conventions. Following [XPath 1.0], function names are composed of English words separated by hyphens,"-". If a function name contains a [XML Schema Part 2: Datatypes] datatype name, it may have intercapitalized spelling and is used in the function name as such. For example, fn:get-timezone-from-dateTime.

As is customary, the parameter type name indicates that the function accepts arguments of that type, or types derived from it, in that position. This is called subtype substitution. Details of the semantics of passing arguments to functions are discussed in Section B.1 Type Promotion^XQ .

Some functions accept the empty sequence as an argument and some may return the empty sequence. This is indicated in the function signature by following the parameter or return type name with a question mark: "?", indicating that either a single value or the empty sequence must appear. See below.

Note that this function signature is different from a signature in which the parameter is omitted. See, for example, the two signatures for fn:string(). In the first signature, the parameter is omitted and the argument defaults to the context-item(.). In the second signature, the argument must be present but may be the empty sequence ().

Some functions accept a sequence as an argument. This is indicated by following the name of type of the items in the sequence with *. The sequence may contain zero or more items of the named type. For example, the function below accepts a sequence of xs:double and returns a xs:double or the empty sequence.

1.3 Namespace Terminology

This document uses the phrase "namespace URI" to identify the concept identified in [Namespaces in XML] as "namespace name", and the phrase "local name" to identify the concept identified in [Namespaces in XML] as "local part".

It also uses the term "expanded-QName".

[Definition] Expanded-QName

An expanded-QName is a pair of values consisting of a namespace URI and a local name. They belong to the value space of the [XML Schema Part 2: Datatypes]datatype xs:QName. When this document refers to xs:QName we always mean the value space, i.e. a namespace URI, local name pair (and not the lexical space referring to constructs of the form prefix:local-name).

1.4 Type Hierarchy

The diagram below shows the types for which functions are defined in this document. These include the built-in types defined by [XML Schema Part 2: Datatypes] (shown on the right) as well as types defined in [XPath 2.0] (shown on the left). Solid lines connect a base datatype above to a derived datatype except in the case of xsIDREFS, xs:IDREFS, xs:NMTOKENS, xs:ENTITIES and user-defined list and union types. These types are lists or unions of their parent types(s) rather than true subtypes. Dashed lines connect a union type above with its component types below.

The information in the above diagram is reproduced below in tabular form. For ease of presentation the information is divided into three tables. The first table shows the top three layers of the hierarchy starting at xs:anyType. The second table shows the types derived from xdt:anyAtomicType. The third table shows the types defined in [XPath 2.0]

Each type whose name is indented is derived from the type whose name appears nearest above with one less level of indent.

The table below shows the datatypes derived from xdt:anyAtomicType. This includes all the [XML Schema Part 2: Datatypes] built-in datatypes as well as the two totally ordered subtypes of duration defined 9.2 Two Totally Ordered Subtypes of Duration.

Each type whose name is indented is derived from the type whose name appears nearest above with one less level of indent.

The table below shows type hierarchy for the types introduced in [XPath 2.0]. For these types, each type whose name is indented is a component of the union type whose name appears nearest above with one less level of indent.

1.5 xdt:anyAtomicType and xdt:untypedAtomic

1.6 xs:dateTime, xs:date and xs:time values

xs:dateTime, xs:date and xs:time values are represented in the Section 3.3.1 Mapping PSVI Additions to Types^DM as tuples: a xs:dateTime, xs:date or xs:time value without a timezone and a timezone represented as a xdt:dayTimeDuration value. The value space of these types consists of the normalized value for these datatypes. This means that the xs:dateTime, xs:date or xs:time is first normalized to UTC or timezone Z. To create a value from a lexical representation of xs:dateTime, xs:date and xs:time lexical representations that have a timezone are converted to timezone Z as defined by [XML Schema Part 2: Datatypes] and the timezone in the lexical representation is converted to a xdt:dayTimeDuration value. Lexical representations that do not contain a timezone are assumed to be in timezone Z and the timezone part of the value set to the empty sequence "()".

We also define the localized value for a xs:dateTime, xs:date and xs:time as the xs:dateTime, xs:date and xs:time value in its original timezone or no timezone, as the case may be, followed by the timezone represented as a xdt:dayTimeDuration. Lexical representations that do not contain a timezone are given a timezone value set to the empty sequence "()".

1.7 Namespaces and Prefixes

The functions and operators discussed in this document are contained in one of three namespaces (see [Namespaces in XML]) and referenced using a xs:QName. Constructor functions for the built-in datatypes defined in [XML Schema Part 2: Datatypes] discussed in 5 Constructor Functions are in the XML Schema namespace, http://www.w3.org/2001/XMLSchema, and named in this document using the xs: prefix. The namespace prefix used in this document is fn: for the functions available to users and op: for the operator functions. The purpose of the functions indicated by the op: prefix is to define the semantics of operators in the host languages. In [XQuery 1.0: An XML Query Language] and [XPath 2.0] they are not directly accessible by users.

The datatypes described in this document in 1.5 xdt:anyAtomicType and xdt:untypedAtomic and 9.2 Two Totally Ordered Subtypes of Duration are contained in a separate namespace and are named using the prefix xdt:.

The namespace prefix for these functions and datatypes can vary, as long as the prefix is bound to the correct URI.

The URIs of the namespaces are:

• http://www.w3.org/2001/XMLSchema for constructors

• http://www.w3.org/2003/11/xpath-functions for functions.

• http://www.w3.org/2003/11/xpath-datatypes for the datatypes.

The functions defined with an fn: prefix are callable by the user. Functions defined with the op: prefix are described here to underpin the definitions of the operators in [XPath 2.0], [XQuery 1.0: An XML Query Language] and [XSLT 2.0]. These functions are not available directly to users, and there is no requirement that implementations should actually provide these functions. For this reason, no namespace is associated with the op: prefix. For example, multiplication is generally associated with the * operator, but it is described as a function in this document:

1.8 Terminology

The terminology used to describe the functions and operators on [XML Schema Part 2: Datatypes] is defined in the body of this specification. The terms defined in the following list are used in building those definitions:

[Definition] for compatibility

A feature of this specification included to ensure that implementations that use this feature remain compatible with [XPath 1.0]

[Definition] may

Conforming documents and processors are permitted to, but need not, behave as described.

[Definition] must

Conforming documents and processors are required to behave as described; otherwise, they are either non-conformant or else in error.

[Definition] implementation defined

Possibly differing between implementations, but specified and documented by the implementor for each particular implementation.

[Definition] implementation-dependent

Possibly differing between implementations, but not specified by this or other W3C specification, and not required to be specified by the implementor for any particular implementation.

[Definition] stable

Most of the functions in the core library have the property that calling the same function twice with the same arguments returns the same result: these functions are said to be stable. This category includes a number of functions such as fn:doc(), fn:collection(), fn:current-dateTime(), fn:current-date and fn:current-time() whose result depends on the external environment. Where the function returns nodes, stability means that the returned nodes are identical, not merely equal. The scope over which the results are stable depends on the processing context. In XSLT, it applies to any two calls on the function executed during the same transformation. In XQuery, it applies to any two calls executed during the evaluation of a top-level expression i.e. an expression not contained in any other expression. In other contexts, the scope is specified by the host environment that invokes the function library.

Some other functions, for example fn:position() and fn:last(), depend on the dynamic context and may, therefore, produce different results each time they are called. These functions are said to be contextual.

2.1 fn:node-name

Summary: Returns an expanded-QName for node kinds that can have names. For other kinds of nodes it returns the empty sequence. If $arg is the empty sequence, the empty sequence is returned.

2.2 fn:string

Summary: Returns the value of $arg represented as a xs:string. If no argument is supplied, this function returns the string value of the context item (.).

If $arg is the empty sequence, the zero-length string is returned.

If $arg is a node, the function returns the string-value of the node, as obtained using the dm:string-value accessor defined in the Section 5.5 string-value Accessor^DM.

If $arg is an atomic value, then the function returns the same string as is returned by the expression "$arg cast as xs:string" (see 17 Casting).

2.3 fn:data

Summary: fn:data takes a sequence of items and returns a sequence of atomic values.

The result of fn:data is the sequence of atomic values produced by applying the following rules to each item in $arg:

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

• If the item is a node, fn:data() returns the typed value of the node as defined by the accessor function dm:typed-value in Section 5.6 typed-value Accessor^DM.

2.4 fn:base-uri

Summary: Returns the value of the base-uri property for $arg as defined by the accessor function dm:base-uri for that kind of node in Section 5.1 base-uri Accessor^DM.

If $arg is the empty sequence, the empty sequence is returned.

Document, element and processing-instruction nodes have a base-uri property which may be empty. The base-uri of all other node types is the empty sequence. If the base-uri property for $arg is non-empty, its value is returned. If the base-uri property for $arg is empty, the base-uri of that node's parent is returned. If the node has no parent, the empty sequence is returned.

Summary: This version of the function returns the value of the base-uri property from the static context using the preceding rules. The static context is discussed in Section 2.1.1 Static Context^XQ .

2.5 fn:document-uri

Summary: Returns the value of the document-uri property for $arg as defined by the accessor function dm:document-uri in Section 5.1 base-uri Accessor^DM.

If $arg is the empty sequence, the empty sequence is returned.

Returns the empty sequence if the node is not a document node or if its document-uri property is a relative URI. Otherwise, returns an absolute URI expressed as an xs:string.

If the document-uri property of $arg is not the empty sequence, then the following expression always holds:

fn:doc(fn:document-uri($arg)) is $arg

3.1 Examples

• fn:error()

• fn:error(xs:QName("xdt:FOAR0003"))

• fn:error("Catch Fire and Burn!")

4.1 Examples

• Consider a situation in which a user wants to investigate the actual value passed to a function. Assume that in a particular execution, $v is an xs:decimal with value 124.84. Writing fn:trace($v, 'the value of $v is:') will put the strings "124.84" and "the value of $v is" in the trace data set in implementation defined order.

5.1 Constructor Functions for XML Schema Built-in Types

Every built-in atomic type that is defined in [XML Schema Part 2: Datatypes], except xs:NOTATION has an associated constructor function; as do xdt:untypedAtomic, defined in 1.5 xdt:anyAtomicType and xdt:untypedAtomic and the two derived types xdt:yearMonthDuration and xdt:dayTimeDuration defined in 9.2 Two Totally Ordered Subtypes of Duration. The form of that function for a type pref:TYPE is:

For example, the signature of the constructor function corresponding to the xs:unsignedInt type defined in [XML Schema Part 2: Datatypes] is:

Invoking the constructor function xs:unsignedInt(12) returns the xs:unsignedInt value 12. Another invocation of that constructor function that returns the same xs:unsignedInt value is xs:unsignedInt("12"). The same result would also be returned if the constructor function were to be invoked with a node that had a value equal to the xs:unsignedInt 12. The standard features described in Section 2.3.2 Atomization^XQ would 'atomize' the node to extract its value and then call the constructor with that value. If the value passed to a constructor is illegal for the datatype to be constructed, an error is raised [invalid value for constructor].

If the argument to a constructor function is an xs:string, whitespace normalization is applied as indicated by the whiteSpace facet for the datatype. The resulting whitespace-normalized string must be a valid lexical form for the type, as specified in [XML Schema Part 2: Datatypes]. The semantics of constructor functions when invoked with a xs:string are identical to XML Schema validation. In the case of xs:dateTime, xs:date and xs:time, the value returned differs from [XML Schema Part 2: Datatypes] and is defined in 1.6 xs:dateTime, xs:date and xs:time values.

The semantics of the constructor function "xs:TYPE(arg)" are identical to the semantics of "arg cast as xs:TYPE". See 17 Casting. In some cases, the semantics of casting are explained using constructor functions; but there is no circularity. The constructors used invariably take xs:string arguments and, in this case, the semantics are the semantics of XML Schema validation as discussed above.

If the argument to a constructor function is a literal, the result of the function may be evaluated statically; if an error is found during such evaluation, it may be reported as a static error.

The following constructor functions for the built-in types are supported:

• xs:string($arg as xdt:anyAtomicType) as xs:string
• xs:boolean($arg as xdt:anyAtomicType) as xs:boolean
• xs:decimal($arg as xdt:anyAtomicType) as xs:decimal
• xs:float($arg as xdt:anyAtomicType) as xs:float

  Implementations ·may· return negative zero for xs:float("-0.0E0").

• xs:double($arg as xdt:anyAtomicType) as xs:double

  Implementations ·may· return negative zero for xs:double("-0.0E0").

• xs:duration($arg  as xdt:anyAtomicType) as xs:duration
• xs:dateTime($arg  as xdt:anyAtomicType) as (xs:dateTime, xdt:dayTimeDuration)
• xs:time($arg as xdt:anyAtomicType) as (xs:time, xdt:dayTimeDuration)
• xs:date($arg as xdt:anyAtomicType) as (xs:date, xdt:dayTimeDuration)
• xs:gYearMonth($arg as xdt:anyAtomicType) as xs:gYearMonth
• xs:gYear($arg as xdt:anyAtomicType) as xs:gYear
• xs:gMonthDay($arg as xdt:anyAtomicType) as xs:gMonthDay
• xs:gDay($arg as xdt:anyAtomicType) as xs:gDay
• xs:gMonth($arg as xdt:anyAtomicType) as xs:gMonth
• xs:hexBinary($arg as xdt:anyAtomicType) as xs:hexBinary
• xs:base64Binary($arg as xdt:anyAtomicType) as xs:base64Binary
• xs:anyURI($arg as xdt:anyAtomicType) as xs:anyURI
• xs:QName($arg as xdt:anyAtomicType) as xs:QName

  See 17.14 Casting to xs:QName for semantics of xs:QName.

• xs:normalizedString($arg as xdt:anyAtomicType) as xs:normalizedString
• xs:token($arg as xdt:anyAtomicType) as xs:token