XSLT Cookbook

Performing a Postorder Traversal

Problem

You want to recursively process the children of an element first and then the element itself.

Solution

Solutions to this recipe have the following general form:

<xsl:template match="node(  )">
     <!--Process children -->
     <xsl:apply-templates/>
   
     <!-- Do something with current node -->
   
</xsl:template>

Discussion

The term postorder is computer-science jargon for traversing a tree so that you recursively visit the children of the root in postorder and then visit the root. This algorithm produces a stylesheet that processes the outermost leaf nodes and works its way up to the document root.

You can apply a postorder traversal to the organizational chart (orgchart.xml) to produce an explanation of who reports to whom, starting from the bottom, as shown in Example 4-21. Example 4-22 shows the output.

Example 4-21. Stylesheet

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:output method="text"/> <xsl:strip-space elements="*"/> <xsl:template match="/employee" priority="10"> <xsl:apply-templates/> <xsl:value-of select="@name"/><xsl:text> is the head of the company. </xsl:text> <xsl:call-template name="reportsTo"/> <xsl:call-template name="HimHer"/> <xsl:text>. </xsl:text> <xsl:text>&#xa;&#xa;</xsl:text> </xsl:template> <xsl:template match="employee[employee]"> <xsl:apply-templates/> <xsl:value-of select="@name"/><xsl:text> is a manager. </xsl:text> <xsl:call-template name="reportsTo"/> <xsl:call-template name="HimHer"/> ...