XQuery Module

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

Conventions

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.

Evaluation

xquery:eval

Updated with Version 11: The Clark notation was replaced with the Expanded QNames notation.

Signature	xquery:eval( $query as xs:anyAtomicType, $bindings as map(*)? := map { }, $options as map(*)? := 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 Expanded QNames 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:get('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

Signature	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:get('tmp')/*, update:output('TEMPORARY DATABASE WAS CLEANED UP') ")

Parsing

xquery:parse

Signature	xquery:parse( $query as xs:anyAtomicType, $options as map(*)? := map { } ) as item()?
Summary	Parses the specified $query as XQuery module and returns the resulting query plan. 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. 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>

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

Updated with Version 11: Options added.

Signature	xquery:fork-join( $functions as function(*)*, $options as map(*)? := map { } ) as item()*
Summary	This function executes the supplied (non-updating) $functions in parallel. The following $options are available: parallel: Maximum number of parallel threads. If the value is smaller than 1, or if the option is omitted, the number of available processors is used. result: Suppress or return the function results (default: true). errors: Ignore or raise errors (default: true).
Examples	Request 100 URLs, use at most 8 parallel threads: xquery:fork-join( for $segment in 1 to 100 let $url := 'http://url.com/path/' || $segment return function() { http:send-request((), $url) }, map { 'parallel': 8 } ) Parallel sleep function calls. The function is expected to finish in 1 second if the system has at least 2 cores: let $f := function() { prof:sleep(1000) } return xquery:fork-join(($f, $f))
Errors	error: an unexpected error occurred.

Errors

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

Version 11

• Updated: xquery:fork-join: Options added.
• Updated: The Clark notation was replaced with the Expanded QNames notation.

Version 10

• Deleted: xquery:parse-uri (merged with xquery:parse)
• Updated: xquery:parse: Template:$query can additionally be of type xs:anyURI.

Version 9.2

• Deleted: xquery:invoke, xquery:invoke-update (merged with xquery:eval and xquery:eval-update)

Version 9.0

• Added: xquery:invoke-update
• Updated: xquery:eval: pass option added
• Updated: xquery:parse, xquery:parse-uri: base-uri option added
• Updated: xquery:update renamed to xquery:eval-update
• Updated: error codes updated; errors now use the module namespace

Version 8.5

• Added: xquery:fork-join
• Updated: xquery:eval: 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
• Updated: xquery:parse: pass option added

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.