xquery

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Module

The xquery accessor is exported by the urn:org:ten60:netkernel:ext:xquery module. Import this module to gain access to the accessor.

Syntax

URI

active:xquery

Argument	Rules	Description
operator	Mandatory	the xquery script

Example Usage

DPML

<instr>
  <type>xquery</type>
  <operator>myquery.xml</operator>
  <target>this:response</target>
</instr>

NetKernel Foundation API

req=context.createSubRequest("active:xquery");
req.addArgument("operator", [resource representation, aspect, or URI] );
result=context.issueSubRequest(req);

Purpose

The xquery accessor executes xquery scripts. The xquery script is provided through the operator, it may be a URI to a plain/text source or XML as text enclosed in an <xquery> element.

This xquery implementation uses the Saxon XQuery engine. Xqueries are compiled and cached for optimal performance.

Documents can be sourced by the XQuery - the NetKernel infrastructure is used to resolve URI resources. So for example if we wanted to query a document ffcpl:/lear.xml

<xquery>
  let $operand := document("ffcpl:/lear.xml")/PLAY/ACT[1]/SCENE[1]
  return &lt;SPEECHES&gt; {$operand//SPEECH[SPEAKER='GLOUCESTER']} &lt;/SPEECHES&gt;
</xquery>

Alternatively documents can be passed to a script as a named parameter argument - the argument name must be declared as a variable in the XQuery. So for example if we wanted to pass a document lear.xml as an argument we would have

<instr>
  <type>xquery</type>
  <operator>myquery.xml</operator>
  <lear>ffcpl:/lear.xml</lear>
  <target>this:response</target>
</instr>

And in the XQuery we would need to declare an external variable with the same name.

declare variable $lear as node() external;

XQuery can also be used as a generative scripting language for dynamically creating documents with or without reference to external documents or passed arguments.

Operator Syntax

The xquery accessor requires an xquery script. The xquery script is passed in by the operator either as a URI reference to a plain/text xquery script or in an <xquery> document fragment.

<xquery>
&lt;table&gt;{
  for $y in 1 to 10 return (
    &lt;tr&gt;{
      for $x in 1 to 10 return
        let $bg:=(if($x mod 2 + $y mod 2 &lt;= 0) then "lightgreen"
          else if ($y mod 2 &lt;= 0) then "yellow"
          else if ($x mod 2 &lt;= 0) then "lightblue"
          else "white"),
        $prod:=$x*$y
        return &lt;td align="right" bgcolor="{$bg}"&gt;{
        if ($x &gt; 1 and $y &gt; 1)
          then $prod
          else &lt;b&gt;{$prod}&lt;/b&gt;}&lt;/td&gt;
        }&lt;/tr&gt;,
    "
  ")
}&lt;/table&gt;,"
"
</xquery>

When passing as XML the <xquery> root element should contain an escaped xquery script for execution by the xquery engine. Note it is important that all xml symbols such as angle brackets <, >, are escaped - this can be most easily accomplished by putting the xquery code in a CDATA section.

Example

See XML technology Tour