XQuery 3.1

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This article is part of the XQuery Portal. It summarizes the new features of the XQuery 3.1 and XQuery 3.1 Functions and Operators specifications that are already supported by BaseX.

Please note that not all of the features that are listed on this page are already found in the official specification documents today. You can check out the W3 Bugzilla Tracker to find out more about the most recently added features.


[edit] Maps

A map is a function that associates a set of keys with values, resulting in a collection of key/value pairs. Each key/value pair in a map is called an entry. A key is an arbitrary atomic value, and the associated value is an arbitrary sequence. Within a map, no two entries have the same key, when compared using the eq operator. It is not necessary that all the keys should be mutually comparable (for example, they can include a mixture of integers and strings).

Maps can be constructed as follows:

map { },                                    (: empty map :)
map { 'key': true(), 1984: (<a/>, <b/>) },  (: map with two entries :)
map:merge(                                  (: map with ten entries :)
  for $i in 1 to 10
  return map { $i: 'value' || $i }

The function corresponding to the map has the signature function($key as xs:anyAtomicType) as item()*. The expression $map($key) returns the associated value; the function call map:get($map, $key) is equivalent. For example, if $books-by-isbn is a map whose keys are ISBNs and whose associated values are book elements, then the expression $books-by-isbn("0470192747") returns the book element with the given ISBN. The fact that a map is a function item allows it to be passed as an argument to higher-order functions that expect a function item as one of their arguments. As an example, the following query uses the higher-order function fn:map($f, $seq) to extract all bound values from a map:

let $map := map { 'foo': 42, 'bar': 'baz', 123: 456 }
return fn:for-each(map:keys($map), $map)

This returns some permutation of (42, 'baz', 456).

Because a map is a function item, functions that apply to functions also apply to maps. A map is an anonymous function, so fn:function-name returns the empty sequence; fn:function-arity always returns 1.

Like all other values, maps are immutable. For example, the map:remove function creates a new map by removing an entry from an existing map, but the existing map is not changed by the operation. Like sequences, maps have no identity. It is meaningful to compare the contents of two maps, but there is no way of asking whether they are "the same map": two maps with the same content are indistinguishable.

Maps may be compared using the fn:deep-equal function. The Map Module describes the available set of map functions.

[edit] Arrays

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. The values of an array are called its members. In the type hierarchy, array has a distinct type, which is derived from function. In BaseX, arrays (as well as sequences) are based on an efficient Finger Tree implementation.

Arrays can be constructed in two ways. With the square bracket notation, the comma serves as delimiter:

[],            (: empty array :)
[ (1, 2) ],    (: array with single member :)
[ 1 to 2, 3 ]  (: array with two members; same as: [ (1, 2), 3 ] :)

With the array keyword and curly brackets, the inner expression is evaluated as usual, and the resulting values will be the members of the array:

array { },           (: empty array;              same as: array { () } :)  
array { (1, 2) },    (: array with two members;   same as: array { 1, 2 } :)
array { 1 to 2, 3 }  (: array with three members; same as: array { 1, 2, 3 } :)

The function corresponding to the array has the signature function($index as xs:integer) as item()*. The expression $array($index) returns an addressed member of the array. The following query returns the five array members 48 49 50 51 52 as result:

let $array := array { 48 to 52 }
for $i in 1 to array:size($array)
return $array($i)

Like all other values, arrays are immutable. For example, the array:reverse function creates a new array containing a re-ordering of the members of an existing array, but the existing array is not changed by the operation. Like sequences, arrays have no identity. It is meaningful to compare the contents of two arrays, but there is no way of asking whether they are "the same array": two arrays with the same content are indistinguishable.

[edit] Atomization

If an array is atomized, all of its members will be atomized. As a result, an atomized item may now result in more than one item. Some examples:

fn:data([1 to 2])        (: returns the sequence 1, 2 :)
[ 'a', 'b', 'c' ] = 'b'  (: returns true :)
<a>{ [ 1, 2 ] }</a>      (: returns <a>1 2</a> :)
array { 1 to 2 } + 3     (: error: the left operand returns two items :)

Atomization also applies to function arguments. The following query returns 5, because the array will be atomized to a sequence of 5 integers:

let $f := function($x as xs:integer*) { count($x) }
return $f([1 to 5])

However, the next query returns 1, because the array is already of the general type item(), and no atomization will take place:

let $f := function($x as item()*) { count($x) }
return $f([1 to 5])

Arrays can be compared with the fn:deep-equal function. The Array Module describes the available set of array functions.

[edit] Lookup Operator

The lookup operator provides some syntactic sugar to access values of maps or array members. It is introduced by the question mark (?) and followed by a specifier. The specifier can be:

  1. A wildcard *,
  2. The name of the key,
  3. The integer offset, or
  4. Any other parenthesized expression.

The following example demonstrates the four alternatives:

let $map := map { 'R': 'red', 'G': 'green', 'B': 'blue' }
return (
  $map?*          (: 1. returns all values; same as: map:keys($map) ! $map(.) :),
  $map?R          (: 2. returns the value associated with the key 'R'; same as: $map('R') :),
  $map?('G','B')  (: 3. returns the values associated with the key 'G' and 'B' :)

let $array := [ 'one', 'two', 'three' ]
return (
  $array?*         (: 1. returns all values; same as: (1 to array:size($array)) ! $array(.) :),
  $array?1         (: 2. returns the first value; same as: $array(1) :),
  $array?(2 to 3)  (: 3. returns the second and third values; same as: (1 to 2) ! $array(.) :)

The lookup operator can also be used without left operand. In this case, the context item will be used as input. This query returns Akureyri:

let $maps := (
  map { 'name': 'Guðrún', 'city': 'Reykjavík' },
  map { 'name': 'Hildur', 'city': 'Akureyri' }
return $maps[?name = 'Hildur'] ?city

[edit] Arrow Operator

The arrow operator applies a function to a value. The value is used as the first argument to the function. It is introduced with the characters =>, and it is followed by the function to be called. If $v is a value and f() is a function, then $v=>f() is equivalent to f($v), and $v=>f($j) is equivalent to f($v, $j). This is further illustrated by an example:

(: Returns 3 :)
count(('A', 'B', 'C')),
('A', 'B', 'C') => count(),
('A', 'B', 'C') => (function( $sequence) { count( $sequence)})(),

(: Returns W-E-L-C-O-M-E :)
string-join(tokenize(upper-case('w e l c o m e')), '-'),
'w e l c o m e' => upper-case() => tokenize() => string-join('-'),

(: Returns xfmdpnf :)
  for $i in string-to-codepoints('welcome')
  return $i + 1
(for $i in 'welcome' => string-to-codepoints()
 return $i + 1) => codepoints-to-string()

The syntax makes nested function calls more readable, as it is easy to see if parentheses are balanced.

[edit] String Constructor

The string constructor has been inspired by here document literals of the Unix shell and script languages. It allows you to generate strings that contain various characters that would otherwise be interpreted as XQuery delimiters.

The string constructors syntax uses two backticks and a square bracket for opening and closing a string:

(: Returns "This is a 'new' & 'flexible' syntax." :)
``["This is a 'new' & 'flexible' syntax."]``

XQuery expressions can be embedded via backticks and a curly bracket. The evaluated results will be separated with spaces, and all strings will eventually be concatenated:

(: Returns »Count 1 2 3, and I will be there.« :)
let $c := 1 to 3
return ``[»Count `{ $c }`, and I will be there.«]``

[edit] Serialization

Two Serialization methods have been added to the Serialization spec:

[edit] Adaptive Serialization

The adaptive serialization provides a intuitive textual representation for all XDM types, including maps and arrays, functions, attributes, and namespaces. All items will be separated by the value of the item-separator parameter, which by default is a newline character. It is utilized by the functions prof:dump and fn:trace.


declare option output:method 'adaptive';
<element id='id0'/>/@id,
map { 'key': 'value' },


map {
  "key": "value"

[edit] JSON Serialization

The new json serialization output method can be used to serialize XQuery maps, arrays, atomic values and empty sequences as JSON.

The json output method has been introduced in BaseX quite a while ago. The implementation of this method now complies with the standard serialization rules and, at the same time, preserves the existing semantics:

The following two queries will both return the JSON snippet { "key": "value" }:

declare option output:method 'json';
map { "key": "value" }
declare option output:method 'json';
<json type='object'>

[edit] Functions

The following functions of the XQuery 3.1 Functions and Operators Working Draft have been added. Please be aware that the functions are still subject to change:

[edit] Map Functions

The following map functions are now available:

map:merge, map:size, map:keys, map:contains, map:get, map:entry, map:put, map:remove, map:for-each

Please check out the Map Module for more details.

[edit] Array Functions

The following array functions are now available:

array:size, array:append, array:subarray, array:remove, array:insert-before, array:head, array:tail, array:reverse, array:join, array:flatten, array:for-each, array:filter, array:fold-left, array:fold-right, array:for-each-pair

Please check out the Array Module for more details.

[edit] JSON Functions

XQuery now provides native support for JSON objects. Strings and resources can be parsed to XQuery items and, as shown above, serialized back to their original form.

[edit] fn:parse-json


Parses the supplied string as JSON text and returns its item representation. The result may be a map, an array, a string, a double, a boolean, or an empty sequence. The allowed options can be looked up in the specification.

parse-json('{ "name": "john" }')   (: yields { "name": "json" } :),
parse-json('[ 1, 2, 4, 8, 16]')    (: yields [ 1, 2, 4, 8, 16 ] :)

[edit] fn:json-doc


Retrieves the text from the specified URI, parses the supplied string as JSON text and returns its item representation (see fn:parse-json for more details).

json-doc("http://ip.jsontest.com/")('ip')  (: returns your IP address :)

[edit] fn:json-to-xml


Converts a JSON string to an XML node representation. The allowed options can be looked up in the specification.

json-to-xml('{ "message": "world" }')

(: result:
<map xmlns="http://www.w3.org/2005/xpath-functions">
  <string key="message">world</string>
</map> :)

[edit] fn:xml-to-json


Converts an XML node, whose format conforms to the results created by fn:json-to-xml, to a JSON string representation. The allowed options can be looked up in the specification.

(: returns "JSON" :)
xml-to-json(<string xmlns="http://www.w3.org/2005/xpath-functions">JSON</string>)

[edit] fn:sort

Updated with Version 8.6: Collation argument was inserted between first and second argument.


Returns a new sequence with sorted $input items, using an optional $collation. If a $key function is supplied, it will be applied on all items. The items of the resulting values will be sorted using the semantics of the lt expression.

sort(reverse(1 to 3))                    (: yields 1, 2, 3 :),
reverse(sort(1 to 3))                    (: returns the sorted order in descending order :),
sort((3,-2,1), (), abs#1)                (: yields 1, -2, 3 :),
sort((1,2,3), (), function($x) { -$x })  (: yields 3, 2, 1 :),
sort((1,'a'))                            (: yields an error, as strings and integers cannot be compared :)

[edit] fn:contains-token


The supplied strings will be tokenized at whitespace boundaries. The function returns true if one of the strings equals the supplied token, possibly under the rules of a supplied collation:

contains-token(('a', 'b c', 'd'), 'c')                (: yields true :)
<xml class='one two'/>/contains-token(@class, 'one')  (: yields true :)

[edit] fn:parse-ietf-date


Parses a string in the IETF format (which is widely used on the Internet) and returns a xs:dateTime item:

fn:parse-ietf-date('28-Feb-1984 07:07:07')"              (: yields 1984-02-28T07:07:07Z :),
fn:parse-ietf-date('Wed, 01 Jun 2001 23:45:54 +02:00')"  (: yields 2001-06-01T23:45:54+02:00 :)

[edit] fn:apply


A supplied function is invoked with the arguments supplied by an array. The arity of the function must be the same as the size of the array.


fn:apply(concat#5, array { 1 to 5 })            (: 12345 :)
fn:apply(function($a) { sum($a) }, [ 1 to 5 ])  (: 15 :)
fn:apply(count#1, [ 1,2 ])  (: error (the array has two members) :)

[edit] fn:random-number-generator


Creates a random number generator, using an optional seed. The returned map contains three entries:

The returned random generator is deterministic: If the function is called twice with the same arguments and in the same execution scope, it will always return the same result.


let $rng := fn:random-number-generator()
let $number := $rng('number')               (: returns a random number :)
let $next-rng := $rng('next')()             (: returns a new generator :)
let $next-number := $next-rng('number')     (: returns another random number :)
let $permutation := $rng('permute')(1 to 5) (: returns a random permutation of (1,2,3,4,5) :)
return ($number, $next-number, $permutation)

[edit] fn:format-number

The function has been extended to support scientific notation:

format-number(1984.42, '00.0e0')  (: yields 19.8e2 :)

[edit] fn:tokenize

If no separator is specified as second argument, a string will be tokenized at whitespace boundaries:

fn:tokenize("  a b  c d")  (: yields "a", "b", "c", "d" :)

[edit] fn:trace

The second argument can now be omitted:

fn:trace(<xml/>, "Node: ")/node()  (: yields the debugging output "Node: <xml/>" :),
fn:trace(<xml/>)/node()            (: returns the debugging output "<xml/>" :)

[edit] fn:string-join

The type of the first argument is now xs:anyAtomicType*, and all items will be implicitly cast to strings:

fn:string-join(1 to 3)  (: yields the string "123" :)

[edit] fn:default-language

Returns the default language used for formatting numbers and dates. BaseX always returns en.

[edit] Binary Data

Items of type xs:hexBinary and xs:base64Binary can now be compared against each other. The following queries all yield true:

xs:hexBinary('') < xs:hexBinary('bb'),
xs:hexBinary('aa') < xs:hexBinary('bb'),
max((xs:hexBinary('aa'), xs:hexBinary('bb'))) = xs:hexBinary('bb')

[edit] Collations

XQuery 3.1 provides a new default collation, which allows for a case-insensitive comparison of ASCII characters (A-Z = a-z). This query returns true:

declare default collation 'http://www.w3.org/2005/xpath-functions/collation/html-ascii-case-insensitive';
'HTML' = 'html'

If the ICU Library is downloaded and added to the classpath, the full Unicode Collation Algorithm features get available in BaseX:

(: returns 0 (both strings are compared as equal) :)
compare('a-b', 'ab', 'http://www.w3.org/2013/collation/UCA?alternate=shifted')

[edit] Enclosed Expressions

Enclosed expression is the syntactical term for the expressions that are specified inside a function body, try/catch clauses, node constructors and some other expressions. In the following example expressions, it’s the empty sequence:

declare function local:x() { () };
try { () } catch * { () },
element x { () },
text { () }

With XQuery 3.1, the expression can be omitted. The following query is equivalent to the upper one:

declare function local:x() { };
try { } catch * { },
element x { }
text { }

[edit] Pending Features

The following functions have not been implemented yet:

[edit] Changelog

Version 8.6
Version 8.4
Version 8.2
Version 8.1

Introduced with Version 8.0.

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