XQuery 3.1

This article is part of the XQuery Portal. It summarizes the new features of the XQuery 3.1 Working Draft that are already supported by BaseX.

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.

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.

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 three 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.

Lookup Operator

The lookup operator provides some syntactic sugar to access values of maps or array members at a specified position. 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. an 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 :),
  $map?R         (: 2. returns the value associated with the key 'R'; equivalent to $map('R') :),
  $map?('G','B') (: 4. returns the values associated with the key 'G' and 'B' :)
),

let $array := [ 'one', 'two', 'three' ]
return (
  $array ? *         (: 1. returns all values :),
  $array ? 1         (: 3. returns the first value; equivalent to $array(2) :),
  $array ? (2 to 3)  (: 4. returns the value 2 and 3 :)
)

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:

for $map in (
  map { 'name': 'Guðrún', 'city': 'Reykjavík' },
  map { 'name': 'Hildur', 'city': 'Akureyri' }
)
return $map[? name = 'Hildur'] ? city

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.

Functions

The following functions of the XQuery 3.1 Functions and Operators Working Draft have already been implemented:

• Map functions: map:merge, map:size, map:keys, map:contains, map:get, map:entry, map:put, map:remove, map:for-each-entry
• Array functions: array:size, array:append, array:subarray, array:remove, array:insert-before, array:head, array:tail, array:reverse, array:join, array:for-each-member, array:filter, array:for-each-pair
• fn:contains-token($input as xs:string*, $token as string, $collation as xs:string) as xs:boolean: Checks if the input strings contain a given token.

New signatures have been added for the following functions:

• fn:tokenize($string as xs:string) as xs:string*: Splits a string at whitespace boundaries.

Binary Data

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

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

Pending Features

The features of XQuery 3.1 are still subject to change, but we are planning to add the following enhancements in near future:

• Arrow operator (=>): applies a function to an item, using the item as the first argument to the function. The expression $i=>$f() is equivalent to $f($i), and $i=>$f($j) is equivalent to $f($i, $j).
• Support for JSON: fn:json-doc, fn:parse-json
• New functions: array:fold-left, array:fold-right, fn:collation-key, fn:load-module, fn:parse-ietf-date, fn:transform, map:for-each-entry
• Support for scientific notation: format-number

Changelog

Introduced with Version 8.0.