XSL Hell :-)

nospam@example.com (Manuel Pichler) — Mon, 08 Sep 2008 21:08:00 +0200

While traveling from Cologne to Schwelm I was working on a xsl stylesheet that produces odd/even rows for a list view. Oh, you say: "Not really hard to implement! Why do you blog about such stuff?" Either I am totally blind or the odd/even topic is really hard to solve problem for recursive, tree like structures, so please: "repeat this answer/question for the following xsl fragment"

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
<xsl:template name="is.odd.or.even">
<xsl:param name="c" select="1" />
<xsl:param name="n" select="." />
<xsl:choose>
<xsl:when test="name($n) = 'testcase' and $n/preceding-sibling::*">
<xsl:call-template name="is.odd.or.even">
<xsl:with-param name="c" select="$c + 1" />
<xsl:with-param name="n" select="$n/preceding-sibling::*[1]" />
</xsl:call-template>
</xsl:when>
<xsl:when test="name($n) = 'testsuite' and $n/preceding-sibling::*">
<xsl:variable name="preceding" select="$n/preceding-sibling::*[1]" />
<xsl:variable name="child.count" select="count($preceding//testcase) +
count($preceding//testsuite)" />
<xsl:call-template name="is.odd.or.even">
<xsl:with-param name="c" select="$c + 1 + $child.count" />
<xsl:with-param name="n" select="$preceding" />
</xsl:call-template>
</xsl:when>
<xsl:when test="(name($n) = 'testcase' or name($n) = 'testsuite') and contains($n/../@name, '::')">
<xsl:call-template name="is.odd.or.even">
<xsl:with-param name="c" select="$c + 1" />
<xsl:with-param name="n" select="$n/.." />
</xsl:call-template>
</xsl:when>
<xsl:otherwise>
<xsl:if test="$c mod 2 = 1">
<xsl:text>oddrow</xsl:text>
</xsl:if>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>

xpathing

nospam@example.com (Manuel Pichler) — Tue, 03 Jul 2007 21:20:00 +0200

Have you ever worked with external xml documents where you don't know the hole structure or exactly all the used namespaces? It's a pain. Such a situation occured for one of our user group members, when he had to process a complex rdf document with multiple different xml markups.

The following listing shows a modified and simplified version of this rdf document

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about="resource" xmlns:br="http://binary.resource/">
<br:length />1024</br:length>
</rdf:Description>
<rdf:Description rdf:about="meta" xmlns:bm="http://binary.meta/">
<bm:author>Manuel Pichler</bm:author>
<bm:published>2007-07-03</bm:published>
</rdf:Description>
<rdf:Description rdf:about="more" xmlns:bmore="http://binary.more/">
<bmore:more>more and more and more namespaces</bmore:more>
</rdf:Description>
</rdf:RDF>

How would you handle such a structure where you know all or almost all possible markups, but each is optional? The design for the Document Object Model (DOM) assumes that you know all used namespaces in a document. Ok you can use getElementsByTagNameNS() and getAttributeNodeNS() with the asterisk character as argument to fetch all namespaced nodes. Which leads to the following code to find all used namespaces.

<?php
$dom = new DOMDocument();
$dom->load( "xpath.xml" );

$foundNS = {FNAMEL}">array();

$nodes = $dom->getElementsByTagNameNS( "*", "*" );

foreach ( $nodes as $node )
{
if ( $node->namespaceURI === "http://www.w3.org/1999/02/22-rdf-syntax-ns#" )
{
continue;
}
if ( {FNAMEL}">isset( $foundNS[$node->namespaceURI ] ) )
{
continue;
}

$foundNS[$node->namespaceURI] = true;

{FNAMEL}">print "ns-prefix: {$node->prefix}, ns-uri: {$node->namespaceURI}\n";
}
?>

This could be a good solution for small documents, but consider really large documents with thousands of elements where each element is part of a namespace. This solution would load all these nodes into user land code and check there for an unknown/unvisited namespace which will be very expensive. So we have to find another solution for our problem. And here comes XPath into the play. XPath provides a large set of functions and constructs that help solving this problem.

<?php
$dom = new DOMDocument();
$dom->load( "xpath.xml" );

$xp = new DOMXPath( $dom );
$xp->registerNamespace( "rdf", "http://www.w3.org/1999/02/22-rdf-syntax-ns#" );

$nodes = $xp->evaluate(
"//*[ name(.) = 'rdf:Description'
]/*[ namespace-uri(.) != namespace-uri(..) and
namespace-uri(.) != '' and
namespace-uri(.) != namespace-uri(preceding-sibling::*)]" );

foreach ( $nodes as $node )
{
{FNAMEL}">print "ns-prefix: {$node->prefix}, ns-uri: {$node->namespaceURI}\n";
}
?>

What we do here is. We look for the rdf:Description elements which are the parents for all unknown namespaces. Then we search for all elements with a namespace namespace-uri(.) != '' that is not equal to the rdf namespace namespace-uri(.) != namespace-uri(..). But there are multiple elements with the same namespace so we have to unify the result which is done with namespace-uri(.) != namespace-uri(preceding-sibling::*).

Comments and optimizations are very welcome.

Manuel Pichler - xml

XSL Hell :-)

xpathing