Difference between revisions of "XQuery Module"

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This [[Module Library|XQuery Module]] contains functions to evaluate XQuery strings and modules at runtime.
+
This [[Module Library|XQuery Module]] contains functions for parsing and evaluating XQuery strings at runtime, and to run code in parallel.
  
 
=Conventions=
 
=Conventions=
  
All functions in this module are assigned to the {{Code|http://basex.org/modules/xquery}} namespace, which is statically bound to the {{Code|xquery}} prefix.<br/>
+
All functions and errors in this module are assigned to the <code><nowiki>http://basex.org/modules/xquery</nowiki></code> namespace, which is statically bound to the {{Code|xquery}} prefix.<br/>
All errors are assigned to the {{Code|http://basex.org/errors}} namespace, which is statically bound to the {{Code|bxerr}} prefix.
 
  
=Functions=
+
=Dynamic Evaluation=
  
 
==xquery:eval==
 
==xquery:eval==
 +
 
{| width='100%'
 
{| width='100%'
 
|-
 
|-
| width='90' | '''Signatures'''
+
| width='120' | '''Signatures'''
|{{Func|xquery:eval|$query as xs:string|item()*}}<br />{{Func|xquery:eval|$query as xs:string, $bindings as map(*)|item()*}}<br />
+
|{{Func|xquery:eval|$query as xs:anyAtomicType|item()*}}<br />{{Func|xquery:eval|$query as xs:anyAtomicType, $bindings as map(*)?|item()*}}<br />{{Func|xquery:eval|$query as xs:anyAtomicType, $bindings as map(*)?, $options as map(*)?|item()*}}<br />
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Evaluates {{Code|$query}} as XQuery expression at runtime and returns the resulting items.<br />Variables and context items can be declared via {{Code|$bindings}}. The specified keys must be QNames or strings, the values can be arbitrary item sequences:
+
|Evaluates the supplied {{Code|$query}} and returns the resulting items. If the query is of type {{Code|xs:anyURI}}, the module located at this URI will be retrieved (a relative URI will be resolved against the static base URI). Otherwise, the input is expected to be of type {{Code|xs:string}}.
* variables specified as QNames will be directly interpreted as variable name.
+
Variables and context items can be declared via {{Code|$bindings}}. The specified keys must be QNames or strings:
* variables specified as xs:string may be prefixed with a dollar sign. Namespace can be specified using the [http://www.jclark.com/xml/xmlns.htm Clark Notation].
+
* If a key is a QName, it will be directly adopted as variable name.
 +
* It a key is a string, it may be prefixed with a dollar sign. Namespace can be specified using the [http://www.jclark.com/xml/xmlns.htm Clark Notation].
 
* If the specified string is empty, the value will be bound to the context item.
 
* If the specified string is empty, the value will be bound to the context item.
 +
The {{Code|$options}} parameter contains evaluation options:
 +
* {{Code|permission}}: the query will be evaluated with the specified permissions (see [[User Management]]).
 +
* {{Code|timeout}}: query execution will be interrupted after the specified number of seconds.
 +
* {{Code|memory}}: query execution will be interrupted if the specified number of megabytes will be exceeded. This check works best if only one process is running at the same time. Moreover, please note that this option enforces garbage collection, so it will take some additional time, and it requires GC to be enabled in your JVM.
 +
* {{Code|base-uri}}: set [https://www.w3.org/TR/xquery-31/#dt-static-base-uri base-uri property] for the query. Overwrites the base URI of the query; will be used when resolving relative URIs by functions such as {{Code|fn:doc}}.
 +
* {{Code|pass}}: passes on the original error info (line and column number, optional file uri). By default, this option is {{Code|false}}.
 
|-
 
|-
 
| '''Errors'''
 
| '''Errors'''
|{{Error|BXXQ0001|#Errors}} the query contains [[XQuery Update#Updating Expressions|updating expressions]].
+
|{{Error|update|#Errors}} the query contains [[XQuery Update#Updating Expressions|updating expressions]].<br/>{{Error|permission|#Errors}} insufficient permissions for evaluating the query.<br/>{{Error|timeout|#Errors}} query execution exceeded timeout.<br/>{{Error|limit|#Errors}} query execution exceeded memory limit.<br/>{{Error|nested|#Errors}} nested query evaluation is not allowed.<br/>Any other error that may occur while evaluating the query.
 
|-
 
|-
 
| '''Examples'''
 
| '''Examples'''
 
|
 
|
 
* {{Code|xquery:eval("1+3")}} returns {{Code|4}}.<br />
 
* {{Code|xquery:eval("1+3")}} returns {{Code|4}}.<br />
 +
* If a URI is supplied, the query in the specified file will be evaluated:
 +
<syntaxhighlight lang="xquery">
 +
xquery:eval(xs:anyURI('cleanup.xq'))
 +
</syntaxhighlight>
 
* You can bind the context and e.g. operate on a certain database only:<br />
 
* You can bind the context and e.g. operate on a certain database only:<br />
<pre class='brush:xquery'>
+
<syntaxhighlight lang="xquery">
xquery:eval("//country", map{ '' := db:open('factbook') })
+
xquery:eval("//country", map { '': db:open('factbook') })
</pre>
+
</syntaxhighlight>
 
* The following expressions use strings as keys. All of them return 'XML':<br/>
 
* The following expressions use strings as keys. All of them return 'XML':<br/>
<pre class='brush:xquery'>
+
<syntaxhighlight lang="xquery">
xquery:eval(".", map{ '' := 'XML' })
+
xquery:eval(".", map { '': 'XML' }),
xquery:eval("$xml", map{ 'xml' := 'XML' }),
+
 
xquery:eval("$xml", map{ '$xml' := 'XML' }),
+
xquery:eval("declare variable $xml external; $xml", map { 'xml': 'XML' }),
xquery:eval("declare namespace pref='URI'; $pref:xml", map{ '{URI}xml' := 'XML' }),
+
 
</pre>
+
xquery:eval(
 +
  "declare namespace pref='URI';
 +
  declare variable $pref:xml external;
 +
  $pref:xml",
 +
  map { '{URI}xml': 'XML' }
 +
)
 +
</syntaxhighlight>
 
* The following expressions use QNames as keys. All of them return 'XML':<br/>
 
* The following expressions use QNames as keys. All of them return 'XML':<br/>
<pre class='brush:xquery'>
+
<syntaxhighlight lang="xquery">
 
declare namespace pref = 'URI';
 
declare namespace pref = 'URI';
xquery:eval("$xml", map{ xs:QName('xml') := 'XML' })
+
 
xquery:eval("declare namespace pref='URI'; $pref:xml", map{ xs:QName('pref:xml') := 'XML' }),
+
xquery:eval("declare variable $xml external; $xml", map { xs:QName('xml'): 'XML' }),
</pre>
+
 
 +
let $query := "declare namespace pref='URI';
 +
              declare variable $pref:xml external;
 +
              $pref:xml"
 +
let $vars := map { xs:QName('pref:xml'): 'XML' }
 +
return xquery:eval($query, $vars)
 +
</syntaxhighlight>
 +
|}
 +
 
 +
==xquery:eval-update==
 +
 
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|xquery:eval-update|$query as xs:anyAtomicType|item()*}}<br />{{Func|xquery:eval-update|$query as xs:anyAtomicType, $bindings as map(*)?|item()*}}<br />{{Func|xquery:eval-update|$query as xs:anyAtomicType, $bindings as map(*)?, $options as map(*)?|item()*}}<br />
 +
|-
 +
| '''Summary'''
 +
|Evaluates a query as updating expression. All updates will be added to the [[XQuery Update#Pending Update List|Pending Update List]] of the main query and performed after the evaluation of the main query.<br />The rules for all arguments are the same as for [[#xquery:eval|xquery:eval]].
 +
|-
 +
| '''Errors'''
 +
|{{Error|update|#Errors}} the query contains no [[XQuery Update#Updating Expressions|updating expressions]].<br/>{{Error|permission|#Errors}} insufficient permissions for evaluating the query.<br/>{{Error|timeout|#Errors}} query execution exceeded timeout.<br/>{{Error|limit|#Errors}} query execution exceeded memory limit.<br/>{{Error|nested|#Errors}} nested query evaluation is not allowed.<br/>Any other error that may occur while evaluating the query.
 +
|-
 +
| '''Examples'''
 +
|
 +
* Removes entries from a temporary databases and returns an info string:
 +
<syntaxhighlight lang="xquery">
 +
xquery:eval-update("
 +
  delete node db:open('tmp')/*,
 +
  update:output('TEMPORARY DATABASE WAS CLEANED UP')
 +
")
 +
</syntaxhighlight>
 
|}
 
|}
  
==xquery:invoke==
+
=XQuery Parsing=
 +
 
 +
==xquery:parse==
 +
 
 
{| width='100%'
 
{| width='100%'
 
|-
 
|-
| width='90' | '''Signatures'''
+
| width='120' | '''Signatures'''
|{{Func|xquery:invoke|$uri as xs:string|item()*}}<br />{{Func|xquery:invoke|$expr as xs:string, $bindings as map(*)|item()*}}<br />
+
|{{Func|xquery:parse|$query as xs:string|item()?}}<br />{{Func|xquery:parse|$query as xs:string, $options as map(*)?|item()?}}<br />
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Opens {{Code|$uri}} as file, evaluates it as XQuery expression at runtime, and returns the resulting items.<br />The semantics of the {{Code|$bindings}} parameter is the same as for [[#xquery:eval|xquery:eval]].
+
|Parses the specified {{Code|$query}} string as XQuery module and returns the resulting query plan. The {{Code|$options}} parameter influences the output:
 +
* {{Code|compile}}: additionally compiles the query after parsing it. By default, this option is {{Code|false}}.
 +
* {{Code|plan}}: returns an XML representation of the internal query plan. By default, this option is {{Code|true}}. The naming of the expressions in the query plan may change over time
 +
* {{Code|pass}}: by default, the option is {{Code|false}}. If an error is raised, the line/column number and the optional file uri will refer to the location of the function call. If the option is enabled, the line/column and file uri will be adopted from the raised error.
 +
* {{Code|base-uri}}: set [https://www.w3.org/TR/xquery-31/#dt-static-base-uri base-uri property] for the query. This URI will be used when resolving relative URIs by functions such as {{Code|fn:doc}}.
 
|-
 
|-
 
| '''Errors'''
 
| '''Errors'''
|{{Error|BXXQ0001|#Errors}} the query contains [[XQuery Update#Updating Expressions|updating expressions]].
+
|Any error that may occur while parsing the query.
 +
|-
 +
| '''Examples'''
 +
|
 +
* {{Code|xquery:parse("1 + 3")}} returns:
 +
<syntaxhighlight lang="xml">
 +
<MainModule updating="false">
 +
  <QueryPlan compiled="false">
 +
    <Arith op="+">
 +
      <Int value="1" type="xs:integer"/>
 +
      <Int value="3" type="xs:integer"/>
 +
    </Arith>
 +
  </QueryPlan>
 +
</MainModule>
 +
</syntaxhighlight>
 
|}
 
|}
  
==xquery:type==
+
==xquery:parse-uri==
  
 
{| width='100%'
 
{| width='100%'
 
|-
 
|-
| width='90' | '''Signatures'''
+
| width='120' | '''Signatures'''
|{{Func|xquery:type|$expr as item()*|item()*}}
+
|{{Func|xquery:parse-uri|$uri as xs:string|item()?}}<br />{{Func|xquery:parse-uri|$uri as xs:string, $options as map(*)?|item()?}}<br />
 
|-
 
|-
 
| '''Summary'''
 
| '''Summary'''
|Similar to {{Code|fn:trace($expr, $msg)}}, but instead of a user-defined message, it emits the compile-time type and estimated result size of its argument.
+
|Parses the XQuery module located at {{Code|$uri}} and returns the resulting query plan. A relative URI will be resolved against the static base URI of the query. The rules for the {{Code|$options}} parameter are the same as for [[#xquery:parse|xquery:parse]].
 +
|-
 +
| '''Errors'''
 +
|Any error that may occur while parsing the query.
 +
|}
 +
 
 +
=Parallelized Execution=
 +
 
 +
Parallel query execution is recommendable if you have various calls that require a lot of time, but that cannot be sped up by rewriting the code. This is e. g. the case if external URLs are called. If you are parallelizing local data reads (such as the access to a database), single-threaded queries will usually be faster, because parallelized access to disk data often results in randomized access patterns, which will rarely be optimized by the caching strategies of HDDs, SSDs, or the operating system.
 +
 
 +
==xquery:fork-join==
 +
 
 +
{| width='100%'
 +
|-
 +
| width='120' | '''Signatures'''
 +
|{{Func|xquery:fork-join|$functions as function(*)*|item()*}}
 +
|-
 +
|'''Summary'''
 +
|This function executes the supplied (non-updating) functions in parallel.
 +
|-
 +
| '''Examples'''
 +
|
 +
* The following function sleeps in parallel; it will be finished in 1 second if your system has at least 2 cores:
 +
<syntaxhighlight lang="xquery">
 +
let $f := function() { prof:sleep(1000) }
 +
return xquery:fork-join(($f, $f))
 +
</syntaxhighlight>
 +
* In the following query, up to four URLs will be requested in parallel:
 +
<syntaxhighlight lang="xquery">
 +
xquery:fork-join(
 +
  for $segment in 1 to 4
 +
  let $url := 'http://url.com/path/' || $segment
 +
  return function() { http:send-request((), $url) }
 +
)
 +
</syntaxhighlight>
 +
|-
 +
|'''Errors'''
 +
|{{Error|error|#Errors}} an unexpected error occurred.
 
|}
 
|}
  
 
=Errors=
 
=Errors=
  
{| width='100%' class="wikitable" width="100%"
+
{| class="wikitable" width="100%"
! width="5%"|Code
+
! width="110"|Code
! width="95%"|Description
+
|Description
 +
|-
 +
|{{Code|permission}}
 +
|Insufficient permissions for evaluating the query.
 +
|-
 +
|{{Code|update}}
 +
|[[XQuery Update#Updating Expressions|updating expression]] found or expected.
 
|-
 
|-
|{{Code|BXXQ0001}}
+
|{{Code|timeout}}
|A dynamically evaluated query must not contain any [[XQuery Update#Updating Expressions|updating expressions]].
+
|Query execution exceeded timeout.
 +
|-
 +
|{{Code|memory}}
 +
|Query execution exceeded memory limit.
 +
|-
 +
|{{Code|nested}}
 +
|Nested query evaluation is not allowed.
 +
|-
 +
|{{Code|error}}
 +
|An unexpected error occurred.
 
|}
 
|}
  
 
=Changelog=
 
=Changelog=
 +
 +
;Version 9.2
 +
 +
* Deleted: xquery:invoke, xquery:invoke-update (merged with [[#xquery:eval|xquery:eval]] and [[#xquery:eval-update|xquery:eval-update]])
 +
 +
;Version 9.0
 +
 +
* Added: [[#xquery:invoke-update|xquery:invoke-update]]
 +
* Updated: [[#xquery:eval|xquery:eval]]: {{Code|pass}} option added
 +
* Updated: [[#xquery:parse|xquery:parse]], [[#xquery:parse-uri|xquery:parse-uri]]: {{Code|base-uri}} option added
 +
* Updated: xquery:update renamed to [[#xquery:eval-update|xquery:eval-update]]
 +
* Updated: error codes updated; errors now use the module namespace
 +
 +
;Version 8.5
 +
 +
* Added: [[#xquery:fork-join|xquery:fork-join]]
 +
* Updated: [[#xquery:eval|xquery:eval]]: {{Code|base-uri}} option added
 +
* Updated: Relative URIs will always be resolved against the static base URI of the query
 +
* Deleted: xquery:type (moved to [[Profiling Module]])
 +
 +
;Version 8.4
 +
 +
* Added: [[#xquery:parse-uri|xquery:parse-uri]]
 +
* Updated: [[#xquery:parse|xquery:parse]]: {{Code|pass}} option added
 +
 +
;Version 8.0
 +
 +
* Added: xquery:update, [[#xquery:parse|xquery:parse]]
 +
* Deleted: xquery:evaluate (opened databases will now be closed by main query)
 +
 +
;Version 7.8.2
 +
 +
* Added: {{Code|$options}} argument
 +
 +
;Version 7.8
 +
 +
* Added: [[#xquery:evaluate|xquery:evaluate]]
 +
* Updated: used variables must be explicitly declared in the query string.
  
 
This module was introduced with Version 7.3. Functions have been adopted from the obsolete Utility Module.
 
This module was introduced with Version 7.3. Functions have been adopted from the obsolete Utility Module.
 
[[Category:XQuery]]
 

Latest revision as of 14:24, 27 February 2020

This XQuery Module contains functions for parsing and evaluating XQuery strings at runtime, and to run code in parallel.

Conventions[edit]

All functions and errors in this module are assigned to the http://basex.org/modules/xquery namespace, which is statically bound to the xquery prefix.

Dynamic Evaluation[edit]

xquery:eval[edit]

Signatures xquery:eval($query as xs:anyAtomicType) as item()*
xquery:eval($query as xs:anyAtomicType, $bindings as map(*)?) as item()*
xquery:eval($query as xs:anyAtomicType, $bindings as map(*)?, $options as map(*)?) as item()*
Summary Evaluates the supplied $query and returns the resulting items. If the query is of type xs:anyURI, the module located at this URI will be retrieved (a relative URI will be resolved against the static base URI). Otherwise, the input is expected to be of type xs:string.

Variables and context items can be declared via $bindings. The specified keys must be QNames or strings:

  • If a key is a QName, it will be directly adopted as variable name.
  • It a key is a string, it may be prefixed with a dollar sign. Namespace can be specified using the Clark Notation.
  • If the specified string is empty, the value will be bound to the context item.

The $options parameter contains evaluation options:

  • permission: the query will be evaluated with the specified permissions (see User Management).
  • timeout: query execution will be interrupted after the specified number of seconds.
  • memory: query execution will be interrupted if the specified number of megabytes will be exceeded. This check works best if only one process is running at the same time. Moreover, please note that this option enforces garbage collection, so it will take some additional time, and it requires GC to be enabled in your JVM.
  • base-uri: set base-uri property for the query. Overwrites the base URI of the query; will be used when resolving relative URIs by functions such as fn:doc.
  • pass: passes on the original error info (line and column number, optional file uri). By default, this option is false.
Errors update: the query contains updating expressions.
permission: insufficient permissions for evaluating the query.
timeout: query execution exceeded timeout.
limit: query execution exceeded memory limit.
nested: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.
Examples
  • xquery:eval("1+3") returns 4.
  • If a URI is supplied, the query in the specified file will be evaluated:
xquery:eval(xs:anyURI('cleanup.xq'))
  • You can bind the context and e.g. operate on a certain database only:
xquery:eval("//country", map { '': db:open('factbook') })
  • The following expressions use strings as keys. All of them return 'XML':
xquery:eval(".", map { '': 'XML' }),

xquery:eval("declare variable $xml external; $xml", map { 'xml': 'XML' }),

xquery:eval(
  "declare namespace pref='URI';
   declare variable $pref:xml external;
   $pref:xml",
  map { '{URI}xml': 'XML' }
)
  • The following expressions use QNames as keys. All of them return 'XML':
declare namespace pref = 'URI';

xquery:eval("declare variable $xml external; $xml", map { xs:QName('xml'): 'XML' }),

let $query := "declare namespace pref='URI';
               declare variable $pref:xml external;
               $pref:xml"
let $vars := map { xs:QName('pref:xml'): 'XML' }
return xquery:eval($query, $vars)

xquery:eval-update[edit]

Signatures xquery:eval-update($query as xs:anyAtomicType) as item()*
xquery:eval-update($query as xs:anyAtomicType, $bindings as map(*)?) as item()*
xquery:eval-update($query as xs:anyAtomicType, $bindings as map(*)?, $options as map(*)?) as item()*
Summary Evaluates a query as updating expression. All updates will be added to the Pending Update List of the main query and performed after the evaluation of the main query.
The rules for all arguments are the same as for xquery:eval.
Errors update: the query contains no updating expressions.
permission: insufficient permissions for evaluating the query.
timeout: query execution exceeded timeout.
limit: query execution exceeded memory limit.
nested: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.
Examples
  • Removes entries from a temporary databases and returns an info string:
xquery:eval-update("
  delete node db:open('tmp')/*,
  update:output('TEMPORARY DATABASE WAS CLEANED UP')
")

XQuery Parsing[edit]

xquery:parse[edit]

Signatures xquery:parse($query as xs:string) as item()?
xquery:parse($query as xs:string, $options as map(*)?) as item()?
Summary Parses the specified $query string as XQuery module and returns the resulting query plan. The $options parameter influences the output:
  • compile: additionally compiles the query after parsing it. By default, this option is false.
  • plan: returns an XML representation of the internal query plan. By default, this option is true. The naming of the expressions in the query plan may change over time
  • pass: by default, the option is false. If an error is raised, the line/column number and the optional file uri will refer to the location of the function call. If the option is enabled, the line/column and file uri will be adopted from the raised error.
  • base-uri: set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc.
Errors Any error that may occur while parsing the query.
Examples
  • xquery:parse("1 + 3") returns:
<MainModule updating="false">
  <QueryPlan compiled="false">
    <Arith op="+">
      <Int value="1" type="xs:integer"/>
      <Int value="3" type="xs:integer"/>
    </Arith>
  </QueryPlan>
</MainModule>

xquery:parse-uri[edit]

Signatures xquery:parse-uri($uri as xs:string) as item()?
xquery:parse-uri($uri as xs:string, $options as map(*)?) as item()?
Summary Parses the XQuery module located at $uri and returns the resulting query plan. A relative URI will be resolved against the static base URI of the query. The rules for the $options parameter are the same as for xquery:parse.
Errors Any error that may occur while parsing the query.

Parallelized Execution[edit]

Parallel query execution is recommendable if you have various calls that require a lot of time, but that cannot be sped up by rewriting the code. This is e. g. the case if external URLs are called. If you are parallelizing local data reads (such as the access to a database), single-threaded queries will usually be faster, because parallelized access to disk data often results in randomized access patterns, which will rarely be optimized by the caching strategies of HDDs, SSDs, or the operating system.

xquery:fork-join[edit]

Signatures xquery:fork-join($functions as function(*)*) as item()*
Summary This function executes the supplied (non-updating) functions in parallel.
Examples
  • The following function sleeps in parallel; it will be finished in 1 second if your system has at least 2 cores:
let $f := function() { prof:sleep(1000) }
return xquery:fork-join(($f, $f))
  • In the following query, up to four URLs will be requested in parallel:
xquery:fork-join(
  for $segment in 1 to 4
  let $url := 'http://url.com/path/' || $segment
  return function() { http:send-request((), $url) }
)
Errors error: an unexpected error occurred.

Errors[edit]

Code Description
permission Insufficient permissions for evaluating the query.
update updating expression found or expected.
timeout Query execution exceeded timeout.
memory Query execution exceeded memory limit.
nested Nested query evaluation is not allowed.
error An unexpected error occurred.

Changelog[edit]

Version 9.2
Version 9.0
Version 8.5
Version 8.4
Version 8.0
  • Added: xquery:update, xquery:parse
  • Deleted: xquery:evaluate (opened databases will now be closed by main query)
Version 7.8.2
  • Added: $options argument
Version 7.8
  • Added: xquery:evaluate
  • Updated: used variables must be explicitly declared in the query string.

This module was introduced with Version 7.3. Functions have been adopted from the obsolete Utility Module.