Performing Set Operations When Querying XML - XSLT 2.0 Enhancements

The main enhancement of XSLT 2.0 is to take advantage of the availability of first-class functions and sequences. This eliminates the need for recursion, the call-back trick, and leads to cleaner definitions and usage. The functions vset:element-equality and vset:member-ofcan still be overridden in importing stylesheets to customize behavior.

  <xsl:stylesheet version="2.0"
  xmlns:xsl="http://www.w3.org/1999/XSL/ Transform"
  xmlns:xs="http://www.w3.org/2001/ XMLSchema"
  xmlns:vset="http:/www.ora.com/XSLTCookbook/ namespaces/vset">

  <!-- The default implementation of element equality. Override in the importing
  stylesheet as necessary. -->
  <xsl:function name="vset:element-equality" as="xs:boolean">
    <xsl:param name="item1" as="item()?"/>
    <xsl:param name="item2" as="item()?"/>
    <xsl:sequence select="$item1 = $item2"/>
  </xsl:function>

  <!-- The default set membership test uses element equality. You will rarely need to
  override this in the importing stylesheet. -->
  <xsl:function name="vset:member-of" as="xs:boolean">
    <xsl:param name="set" as="item()*"/>
    <xsl:param name="elem" as="item()"/>
    <xsl:variable name="member-of" as="xs:boolean*"
                         select="for $test in $set
            return if (vset:element-equality($test, $elem))
                      then true() else ()"/>
    <xsl:sequence select="not(empty($member-of))"/>
  </xsl:function>

  <!-- Compute the union of two sets using "by value" equality. -->
  <xsl:function name="vset:union" as="item()*">
    <xsl:param name="nodes1" as="item()*" />
    <xsl:param name="nodes2" as="item()*" />
   <xsl:sequence select="$nodes1, for $test in $nodes2
                   return if (vset:member-of($nodes1,$test))
                       then () else $test"/>
  </xsl:function>

  <!-- Compute the intersection of two sets using "by value" equality. -->
  <xsl:function name="vset:intersection" as="item()*">
    <xsl:param name="nodes1" as="item()*" />
    <xsl:param name="nodes2" as="item()*" />
   <xsl:sequence select="for $test in $nodes1
                   return if (vset:member-of($nodes2,$test))
                       then $test else ()"/>
  </xsl:function>

  <!-- Compute the difference between two sets (node1 - nodes2) using "by value"
  equality. -->

  <xsl:function name="vset:difference" as="item()*">
    <xsl:param name="nodes1" as="item()*" />
    <xsl:param name="nodes2" as="item()*" />
   <xsl:sequence select="for $test in $nodes1 return if (vset:member-of($nodes2,$test))
  then () else $test"/>
  </xsl:function>

  </xsl:stylesheet>

Next: Equality in Programming >>
 

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