Difference between revisions of "XQuery 3.0"
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'''Example:''' | '''Example:''' | ||
− | < | + | <pre lang='xquery'> |
− | for $country in db: | + | for $country in db:get('factbook')//country |
where $country/@population > 100000000 | where $country/@population > 100000000 | ||
for $city in $country//city[population > 1000000] | for $city in $country//city[population > 1000000] | ||
Line 13: | Line 13: | ||
count $id | count $id | ||
return <country id='{ $id }' name='{ $name }'>{ $city/name }</country> | return <country id='{ $id }' name='{ $name }'>{ $city/name }</country> | ||
− | </ | + | </pre> |
==group by== | ==group by== | ||
Line 20: | Line 20: | ||
'''XQuery:''' | '''XQuery:''' | ||
− | < | + | <pre lang='xquery'> |
for $ppl in doc('xmark')//people/person | for $ppl in doc('xmark')//people/person | ||
let $ic := $ppl/profile/@income | let $ic := $ppl/profile/@income | ||
− | let $income := | + | let $income := |
− | + | if($ic < 30000) then | |
− | + | "challenge" | |
− | + | else if($ic >= 30000 and $ic < 100000) then | |
− | + | "standard" | |
− | + | else if($ic >= 100000) then | |
− | + | "preferred" | |
− | + | else | |
+ | "na" | ||
group by $income | group by $income | ||
order by $income | order by $income | ||
return element { $income } { count($ppl) } | return element { $income } { count($ppl) } | ||
− | </ | + | </pre> |
− | This query is a rewrite of [ | + | This query is a rewrite of [https://www.ins.cwi.nl/projects/xmark/Assets/xmlquery.txt Query #20] contained in the [https://projects.cwi.nl/xmark/ XMark Benchmark Suite] to use <code>group by</code>. |
The query partitions the customers based on their income. | The query partitions the customers based on their income. | ||
'''Result:''' | '''Result:''' | ||
− | < | + | <pre lang="xml"> |
<challenge>4731</challenge> | <challenge>4731</challenge> | ||
<na>12677</na> | <na>12677</na> | ||
<preferred>314</preferred> | <preferred>314</preferred> | ||
<standard>7778</standard> | <standard>7778</standard> | ||
− | </ | + | </pre> |
In contrast to the relational GROUP BY statement, the XQuery counterpart concatenates the values of all non-grouping variables that belong to a specific group. In the context of our example, all nodes in <code>//people/person</code> that belong to the <code>preferred</code> partition are concatenated in <code class="brush:xquery">$ppl</code> after grouping has finished. You can see this effect by changing the return statement to: | In contrast to the relational GROUP BY statement, the XQuery counterpart concatenates the values of all non-grouping variables that belong to a specific group. In the context of our example, all nodes in <code>//people/person</code> that belong to the <code>preferred</code> partition are concatenated in <code class="brush:xquery">$ppl</code> after grouping has finished. You can see this effect by changing the return statement to: | ||
− | < | + | <pre lang='xquery'> |
... | ... | ||
return element { $income } { $ppl } | return element { $income } { $ppl } | ||
− | </ | + | </pre> |
'''Result:''' | '''Result:''' | ||
− | < | + | <pre lang="xml"> |
<challenge> | <challenge> | ||
<person id="person0"> | <person id="person0"> | ||
Line 63: | Line 64: | ||
… | … | ||
</challenge> | </challenge> | ||
− | </ | + | </pre> |
Moreover, a value can be assigned to the grouping variable. This is shown in the following example: | Moreover, a value can be assigned to the grouping variable. This is shown in the following example: | ||
'''XQuery:''' | '''XQuery:''' | ||
− | < | + | <pre lang='xquery'> |
let $data := | let $data := | ||
<xml> | <xml> | ||
Line 76: | Line 77: | ||
</xml> | </xml> | ||
for $person in $data/person | for $person in $data/person | ||
− | group by $country := $person/@country | + | group by $country := $person/@country |
return element persons { | return element persons { | ||
attribute country { $country }, | attribute country { $country }, | ||
− | $person/@name | + | for $name in $person/@name |
+ | return element name { data($name) } | ||
} | } | ||
− | </ | + | </pre> |
'''Result:''' | '''Result:''' | ||
− | < | + | <pre lang="xml"> |
<persons country="USA"> | <persons country="USA"> | ||
<name>John</name> | <name>John</name> | ||
Line 92: | Line 94: | ||
<name>Johann</name> | <name>Johann</name> | ||
</persons> | </persons> | ||
− | </ | + | </pre> |
==count== | ==count== | ||
Line 98: | Line 100: | ||
The {{Code|count}} clause enhances the FLWOR expression with a variable that enumerates the iterated tuples. | The {{Code|count}} clause enhances the FLWOR expression with a variable that enumerates the iterated tuples. | ||
− | < | + | <pre lang='xquery'> |
for $n in (1 to 10)[. mod 2 = 1] | for $n in (1 to 10)[. mod 2 = 1] | ||
count $c | count $c | ||
− | return | + | return <number count="{ $c }" number="{ $n }"/> |
− | </ | + | </pre> |
==allowing empty== | ==allowing empty== | ||
Line 108: | Line 110: | ||
The {{Code|allowing empty}} provides functionality similar to outer joins in SQL: | The {{Code|allowing empty}} provides functionality similar to outer joins in SQL: | ||
− | < | + | <pre lang='xquery'> |
for $n allowing empty in () | for $n allowing empty in () | ||
return 'empty? ' || empty($n) | return 'empty? ' || empty($n) | ||
− | </ | + | </pre> |
==window== | ==window== | ||
Line 117: | Line 119: | ||
Window clauses provide a rich set of variable declarations to process sub-sequences of iterated tuples. An example: | Window clauses provide a rich set of variable declarations to process sub-sequences of iterated tuples. An example: | ||
− | < | + | <pre lang='xquery'> |
for tumbling window $w in (2, 4, 6, 8, 10, 12, 14) | for tumbling window $w in (2, 4, 6, 8, 10, 12, 14) | ||
− | start at $s when | + | start at $s when true() |
only end at $e when $e - $s eq 2 | only end at $e when $e - $s eq 2 | ||
− | return | + | return <window>{ $w }</window> |
− | </ | + | </pre> |
More information on window clauses, and all other enhancements, can be found in the [https://www.w3.org/TR/xquery-30/#id-windows specification]. | More information on window clauses, and all other enhancements, can be found in the [https://www.w3.org/TR/xquery-30/#id-windows specification]. | ||
Line 136: | Line 138: | ||
<ul> | <ul> | ||
<li>Declaring a new ''inline function'': | <li>Declaring a new ''inline function'': | ||
− | < | + | <pre lang='xquery'>let $f := function($x, $y) { $x + $y } |
− | return $f(17, 25)</ | + | return $f(17, 25)</pre> |
'''Result:''' <code>42</code> | '''Result:''' <code>42</code> | ||
</li> | </li> | ||
<li>Getting the function item of an existing (built-in or user-defined) XQuery function. The arity (number of arguments) has to be specified as there can be more than one function with the same name: | <li>Getting the function item of an existing (built-in or user-defined) XQuery function. The arity (number of arguments) has to be specified as there can be more than one function with the same name: | ||
− | < | + | <pre lang='xquery'>let $f := math:pow#2 |
− | return $f(5, 2)</ | + | return $f(5, 2)</pre> |
'''Result:''' <code>25</code> | '''Result:''' <code>25</code> | ||
</li> | </li> | ||
<li>''Partially applying'' another function or function item. This is done by supplying only some of the required arguments, writing the placeholder <code>?</code> in the positions of the arguments left out. The produced function item has one argument for every placeholder. | <li>''Partially applying'' another function or function item. This is done by supplying only some of the required arguments, writing the placeholder <code>?</code> in the positions of the arguments left out. The produced function item has one argument for every placeholder. | ||
− | < | + | <pre lang='xquery'>let $f := substring(?, 1, 3) |
return ( | return ( | ||
$f('foo123'), | $f('foo123'), | ||
$f('bar456') | $f('bar456') | ||
− | )</ | + | )</pre> |
'''Result:''' <code>foo bar</code> | '''Result:''' <code>foo bar</code> | ||
</li> | </li> | ||
</ul> | </ul> | ||
− | Function items can also be passed as arguments to and returned as results from functions. These so-called [[Higher-Order Functions]] like <code> | + | Function items can also be passed as arguments to and returned as results from functions. These so-called [[Higher-Order Functions]] like <code>for-each</code> and <code>fold-left</code> are discussed in more depth on their own Wiki page. |
=Simple Map Operator= | =Simple Map Operator= | ||
Line 162: | Line 164: | ||
'''Example:''' | '''Example:''' | ||
− | < | + | <pre lang='xquery'> |
(: Simple map notation :) | (: Simple map notation :) | ||
(1 to 10) ! element node { . }, | (1 to 10) ! element node { . }, | ||
Line 168: | Line 170: | ||
for $i in 1 to 10 | for $i in 1 to 10 | ||
return element node { $i } | return element node { $i } | ||
− | </ | + | </pre> |
In contrast to path expressions, the results of the map operator will not be made duplicate-free and returned in document order. | In contrast to path expressions, the results of the map operator will not be made duplicate-free and returned in document order. | ||
Line 177: | Line 179: | ||
'''Example:''' | '''Example:''' | ||
− | < | + | <pre lang='xquery'> |
try { | try { | ||
1 + '2' | 1 + '2' | ||
Line 185: | Line 187: | ||
'Error [' || $err:code || ']: ' || $err:description | 'Error [' || $err:code || ']: ' || $err:description | ||
} | } | ||
− | </ | + | </pre> |
'''Result:''' <code>Typing error: '+' operator: number expected, xs:string found.</code> | '''Result:''' <code>Typing error: '+' operator: number expected, xs:string found.</code> | ||
Line 196: | Line 198: | ||
* {{Code|$err:line-number}}: line number where the error occurred | * {{Code|$err:line-number}}: line number where the error occurred | ||
* {{Code|$err:column-number}}: column number where the error occurred | * {{Code|$err:column-number}}: column number where the error occurred | ||
− | |||
=Switch= | =Switch= | ||
Line 203: | Line 204: | ||
'''Example:''' | '''Example:''' | ||
− | < | + | <pre lang='xquery'> |
for $fruit in ("Apple", "Pear", "Peach") | for $fruit in ("Apple", "Pear", "Peach") | ||
return switch ($fruit) | return switch ($fruit) | ||
Line 210: | Line 211: | ||
case "Peach" return "pink" | case "Peach" return "pink" | ||
default return "unknown" | default return "unknown" | ||
− | </ | + | </pre> |
'''Result:''' <code>red green pink</code> | '''Result:''' <code>red green pink</code> | ||
Line 216: | Line 217: | ||
'''Example:''' | '''Example:''' | ||
− | < | + | <pre lang='xquery'> |
for $fruit in ("Apple", "Cherry") | for $fruit in ("Apple", "Cherry") | ||
return switch ($fruit) | return switch ($fruit) | ||
Line 228: | Line 229: | ||
default | default | ||
return "unknown" | return "unknown" | ||
− | </ | + | </pre> |
'''Result:''' <code>red red</code> | '''Result:''' <code>red red</code> | ||
=Expanded QNames= | =Expanded QNames= | ||
− | A ''QName'' can be prefixed with the letter | + | A ''QName'' can be prefixed with the letter {{Code|Q}}, the namespace URI wrapped in curly braces and the local name. |
'''Examples:''' | '''Examples:''' | ||
Line 243: | Line 244: | ||
New namespaces can be created via so-called 'Computed Namespace Constructors'. | New namespaces can be created via so-called 'Computed Namespace Constructors'. | ||
− | < | + | <pre lang='xquery'> |
element node { namespace pref { 'http://url.org/' } } | element node { namespace pref { 'http://url.org/' } } | ||
− | </ | + | </pre> |
=String Concatenations= | =String Concatenations= | ||
− | Two vertical bars <code>||</code> (also named ''pipe characters'') can be used to concatenate strings. This operator is a shortcut for the {{Code| | + | Two vertical bars <code>||</code> (also named ''pipe characters'') can be used to concatenate strings. This operator is a shortcut for the {{Code|concat()}} function. |
− | < | + | <pre lang='xquery'> |
'Hello' || ' ' || 'Universe' | 'Hello' || ' ' || 'Universe' | ||
− | </ | + | </pre> |
=External Variables= | =External Variables= | ||
Line 259: | Line 260: | ||
Default values can be attached to external variable declarations. This way, an expression can also be evaluated if its external variables have not been bound to a new value. | Default values can be attached to external variable declarations. This way, an expression can also be evaluated if its external variables have not been bound to a new value. | ||
− | < | + | <pre lang='xquery'> |
declare variable $user external := "admin"; | declare variable $user external := "admin"; | ||
"User:", $user | "User:", $user | ||
− | </ | + | </pre> |
=Serialization= | =Serialization= | ||
− | [[ | + | [[Serialization]] parameters can be defined within XQuery expressions. Parameters are placed in the query prolog and need to be specified as option declarations, using the <code>output</code> prefix. |
'''Example:''' | '''Example:''' | ||
− | < | + | <pre lang='xquery'> |
declare namespace output = "http://www.w3.org/2010/xslt-xquery-serialization"; | declare namespace output = "http://www.w3.org/2010/xslt-xquery-serialization"; | ||
declare option output:omit-xml-declaration "no"; | declare option output:omit-xml-declaration "no"; | ||
declare option output:method "xhtml"; | declare option output:method "xhtml"; | ||
− | + | <html/> | |
− | </ | + | </pre> |
'''Result:''' <code><?xml version="1.0" encoding="UTF-8"?><html></html></code> | '''Result:''' <code><?xml version="1.0" encoding="UTF-8"?><html></html></code> | ||
Line 284: | Line 285: | ||
'''Example:''' | '''Example:''' | ||
− | < | + | <pre lang='xquery'> |
declare context item := document { | declare context item := document { | ||
<xml> | <xml> | ||
Line 294: | Line 295: | ||
for $t in .//text() | for $t in .//text() | ||
return string-length($t) | return string-length($t) | ||
− | </ | + | </pre> |
'''Result:''' <code>5 5</code> | '''Result:''' <code>5 5</code> | ||
Line 302: | Line 303: | ||
'''Example:''' | '''Example:''' | ||
− | < | + | <pre lang='xquery'> |
declare %private function local:max($x1, $x2) { | declare %private function local:max($x1, $x2) { | ||
if($x1 > $x2) then $x1 else $x2 | if($x1 > $x2) then $x1 else $x2 | ||
Line 308: | Line 309: | ||
local:max(2, 3) | local:max(2, 3) | ||
− | </ | + | </pre> |
=Functions= | =Functions= | ||
Line 314: | Line 315: | ||
The following functions have been added in the [https://www.w3.org/TR/xpath-functions-31/ XQuery 3.0 Functions and Operators] Specification: | The following functions have been added in the [https://www.w3.org/TR/xpath-functions-31/ XQuery 3.0 Functions and Operators] Specification: | ||
− | <code> | + | <code>analyze-string</code>, <code>available-environment-variables</code>, <code>element-with-id</code>, <code>environment-variable</code>, <code>filter</code>, <code>fold-left</code>, <code>fold-right</code>, <code>for-each</code>, <code>for-each-pair</code>, <code>format-date</code>, <code>format-dateTime</code>, <code>format-integer</code>, <code>format-number</code>, <code>format-time</code>, <code>function-arity</code>, <code>function-lookup</code>, <code>function-name</code>, <code>generate-id</code>, <code>has-children</code>, <code>head</code>, <code>innermost</code>, <code>outermost</code>, <code>parse-xml</code>, <code>parse-xml-fragment</code>, <code>path</code>, <code>serialize</code>, <code>tail</code>, <code>unparsed-text</code>, <code>unparsed-text-available</code>, <code>unparsed-text-lines</code>, <code>uri-collection</code> |
New signatures have been added for the following functions: | New signatures have been added for the following functions: | ||
− | <code> | + | <code>document-uri</code>, <code>string-join</code>, <code>node-name</code>, <code>round</code>, <code>data</code> |
=Changelog= | =Changelog= | ||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
;Version 7.7 | ;Version 7.7 |
Latest revision as of 18:38, 1 December 2023
This article is part of the XQuery Portal. It provides a summary of the most important features of the XQuery 3.0 Recommendation.
Contents
Enhanced FLWOR Expressions[edit]
Most clauses of FLWOR expressions can be specified in an arbitrary order: additional let
and for
clauses can be put after a where
clause, and multiple where
, order by
and group by
statements can be used. This means that many nested loops can now be rewritten to a single FLWOR expression.
Example:
for $country in db:get('factbook')//country
where $country/@population > 100000000
for $city in $country//city[population > 1000000]
group by $name := $country/name[1]
count $id
return <country id='{ $id }' name='{ $name }'>{ $city/name }</country>
group by[edit]
FLWOR expressions have been extended to include the group by clause, which is well-established in SQL. group by
can be used to apply value-based partitioning to query results:
XQuery:
for $ppl in doc('xmark')//people/person
let $ic := $ppl/profile/@income
let $income :=
if($ic < 30000) then
"challenge"
else if($ic >= 30000 and $ic < 100000) then
"standard"
else if($ic >= 100000) then
"preferred"
else
"na"
group by $income
order by $income
return element { $income } { count($ppl) }
This query is a rewrite of Query #20 contained in the XMark Benchmark Suite to use group by
.
The query partitions the customers based on their income.
Result:
<challenge>4731</challenge>
<na>12677</na>
<preferred>314</preferred>
<standard>7778</standard>
In contrast to the relational GROUP BY statement, the XQuery counterpart concatenates the values of all non-grouping variables that belong to a specific group. In the context of our example, all nodes in //people/person
that belong to the preferred
partition are concatenated in $ppl
after grouping has finished. You can see this effect by changing the return statement to:
...
return element { $income } { $ppl }
Result:
<challenge>
<person id="person0">
<name>Kasidit Treweek</name>
…
<person id="personX">
…
</challenge>
Moreover, a value can be assigned to the grouping variable. This is shown in the following example:
XQuery:
let $data :=
<xml>
<person country='USA' name='John'/>
<person country='USA' name='Jack'/>
<person country='Germany' name='Johann'/>
</xml>
for $person in $data/person
group by $country := $person/@country
return element persons {
attribute country { $country },
for $name in $person/@name
return element name { data($name) }
}
Result:
<persons country="USA">
<name>John</name>
<name>Jack</name>
</persons>
<persons country="Germany">
<name>Johann</name>
</persons>
count[edit]
The count
clause enhances the FLWOR expression with a variable that enumerates the iterated tuples.
for $n in (1 to 10)[. mod 2 = 1]
count $c
return <number count="{ $c }" number="{ $n }"/>
allowing empty[edit]
The allowing empty
provides functionality similar to outer joins in SQL:
for $n allowing empty in ()
return 'empty? ' || empty($n)
window[edit]
Window clauses provide a rich set of variable declarations to process sub-sequences of iterated tuples. An example:
for tumbling window $w in (2, 4, 6, 8, 10, 12, 14)
start at $s when true()
only end at $e when $e - $s eq 2
return <window>{ $w }</window>
More information on window clauses, and all other enhancements, can be found in the specification.
Function Items[edit]
One of the most distinguishing features added in XQuery 3.0 are function items, also known as lambdas or lambda functions. They make it possible to abstract over functions and thus write more modular code.
Examples:
Function items can be obtained in three different ways:
- Declaring a new inline function:
let $f := function($x, $y) { $x + $y } return $f(17, 25)
Result:
42
- Getting the function item of an existing (built-in or user-defined) XQuery function. The arity (number of arguments) has to be specified as there can be more than one function with the same name:
let $f := math:pow#2 return $f(5, 2)
Result:
25
- Partially applying another function or function item. This is done by supplying only some of the required arguments, writing the placeholder
?
in the positions of the arguments left out. The produced function item has one argument for every placeholder.let $f := substring(?, 1, 3) return ( $f('foo123'), $f('bar456') )
Result:
foo bar
Function items can also be passed as arguments to and returned as results from functions. These so-called Higher-Order Functions like for-each
and fold-left
are discussed in more depth on their own Wiki page.
Simple Map Operator[edit]
The simple map operator !
provides a compact notation for applying the results of a first to a second expression: the resulting items of the first expression are bound to the context item one by one, and the second expression is evaluated for each item. The map operator may be used as replacement for FLWOR expressions:
Example:
(: Simple map notation :)
(1 to 10) ! element node { . },
(: FLWOR notation :)
for $i in 1 to 10
return element node { $i }
In contrast to path expressions, the results of the map operator will not be made duplicate-free and returned in document order.
Try/Catch[edit]
The try/catch construct can be used to handle errors at runtime:
Example:
try {
1 + '2'
} catch err:XPTY0004 {
'Typing error: ' || $err:description
} catch * {
'Error [' || $err:code || ']: ' || $err:description
}
Result: Typing error: '+' operator: number expected, xs:string found.
Within the scope of the catch clause, a number of variables are implicitly declared, giving information about the error that occurred:
$err:code
error code$err:description
: error message$err:value
: value associated with the error (optional)$err:module
: URI of the module where the error occurred$err:line-number
: line number where the error occurred$err:column-number
: column number where the error occurred
Switch[edit]
The switch statement is available in many other programming languages. It chooses one of several expressions to evaluate based on its input value.
Example:
for $fruit in ("Apple", "Pear", "Peach")
return switch ($fruit)
case "Apple" return "red"
case "Pear" return "green"
case "Peach" return "pink"
default return "unknown"
Result: red green pink
The expression to evaluate can correspond to multiple input values.
Example:
for $fruit in ("Apple", "Cherry")
return switch ($fruit)
case "Apple"
case "Cherry"
return "red"
case "Pear"
return "green"
case "Peach"
return "pink"
default
return "unknown"
Result: red red
Expanded QNames[edit]
A QName can be prefixed with the letter Q
, the namespace URI wrapped in curly braces and the local name.
Examples:
Q{http://www.w3.org/2005/xpath-functions/math}pi()
returns the number πQ{java:java.io.FileOutputStream}new("output.txt")
creates a new Java file output stream
Namespace Constructors[edit]
New namespaces can be created via so-called 'Computed Namespace Constructors'.
element node { namespace pref { 'http://url.org/' } }
String Concatenations[edit]
Two vertical bars ||
(also named pipe characters) can be used to concatenate strings. This operator is a shortcut for the concat()
function.
'Hello' || ' ' || 'Universe'
External Variables[edit]
Default values can be attached to external variable declarations. This way, an expression can also be evaluated if its external variables have not been bound to a new value.
declare variable $user external := "admin";
"User:", $user
Serialization[edit]
Serialization parameters can be defined within XQuery expressions. Parameters are placed in the query prolog and need to be specified as option declarations, using the output
prefix.
Example:
declare namespace output = "http://www.w3.org/2010/xslt-xquery-serialization";
declare option output:omit-xml-declaration "no";
declare option output:method "xhtml";
<html/>
Result: <?xml version="1.0" encoding="UTF-8"?><html></html>
In BaseX, the output
prefix is statically bound and can thus be omitted. Note that all namespaces need to be specified when using external APIs, such as XQJ.
Context Item[edit]
The context item can be specified in the prolog of an XQuery expression:
Example:
declare context item := document {
<xml>
<text>Hello</text>
<text>World</text>
</xml>
};
for $t in .//text()
return string-length($t)
Result: 5 5
Annotations[edit]
XQuery 3.0 introduces annotations to declare properties associated with functions and variables. For instance, a function may be declared %public, %private, or %updating.
Example:
declare %private function local:max($x1, $x2) {
if($x1 > $x2) then $x1 else $x2
};
local:max(2, 3)
Functions[edit]
The following functions have been added in the XQuery 3.0 Functions and Operators Specification:
analyze-string
, available-environment-variables
, element-with-id
, environment-variable
, filter
, fold-left
, fold-right
, for-each
, for-each-pair
, format-date
, format-dateTime
, format-integer
, format-number
, format-time
, function-arity
, function-lookup
, function-name
, generate-id
, has-children
, head
, innermost
, outermost
, parse-xml
, parse-xml-fragment
, path
, serialize
, tail
, unparsed-text
, unparsed-text-available
, unparsed-text-lines
, uri-collection
New signatures have been added for the following functions:
document-uri
, string-join
, node-name
, round
, data
Changelog[edit]
- Version 7.7
- Added: Enhanced FLWOR Expressions
- Version 7.3
- Added: Simple Map Operator
- Version 7.2
- Added: Annotations
- Updated: Expanded QNames
- Version 7.1
- Version 7.0
- Added: String Concatenations