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Wednesday, June 22, 2011

Working with namespaces and namespace prefixes in XSLT 1.0

To whom it may concern -

I'm currently developing a Xslt 1.0 stylesheet for analysis of XML Schema documents. As part of this work, I developed a couple of templates for working with namespace names and prefixes, and I like to share them via this post. The code is not incredibly hard or advanced, but it gets the job done and it may save you some time if you need something similar.
  • get-local-name: Return the local name part of a given QName. function in XPath 2.0
  • get-prefix: Return the prefix part of a given QName.
  • get-ns-name: Return the namespace name associated to the given prefix.
  • get-ns-prefix: Return a prefix that can be used to denote the given namespace name.
  • resolve-ns-identifier: Return the namespace name for a given QName prefix
Before I discuss the code, I want to make a few remarks:
  1. This s all about Xslt 1.0 and its query langue XPath 1.0. All these things can be solved much more conveniently in XPath 2.0, and hence in Xslt 2.0 because that builds on Xpath 2.0 (and not XPath 1.0 like Xslt 1.0 does)
  2. If you're planning to use this in a web-browser, and you want to target Firefox, your're out of luck. Sorry. Firefox is a greatt browser, but unlike Chrome, Opera and even Internet Explorer, it doesn't care enough about Xslt to fix bug #94270, which has been living in their bug tracker as long as August 2001 (nope - I didn't mistype 2011, that's 2001 as in almost a decade ago)

get-local-name

Return the local name part of a given QName. This is functionally equivalent to the fn:local-name-from-QName
<!-- get the last substring after the *last* colon (or he argument if no colon) -->
<xsl:template name="get-local-name">
<xsl:param name="qname"/>
<xsl:choose>
<xsl:when test="contains($qname, ':')">
<xsl:call-template name="get-local-name">
<xsl:with-param name="qname" select="substring-after($qname, ':')"/>
</xsl:call-template>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$qname"/>
</xsl:otherwise>
</xsl:choose>
</xsl:template>

get-prefix

Return the prefix part of a given QName. This is functionally equivalent to the fn:prefix-from-QName function in XPath 2.0
<!-- get the substring before the *last* colon (or empty string if no colon) -->
<xsl:template name="get-prefix">
<xsl:param name="qname"/>
<xsl:param name="prefix" select="''"/>
<xsl:choose>
<xsl:when test="contains($qname, ':')">
<xsl:call-template name="get-prefix">
<xsl:with-param name="qname" select="substring-after($qname, ':')"/>
<xsl:with-param name="prefix" select="concat($prefix, substring-before($qname, ':'))"/>
</xsl:call-template>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$prefix"/>
</xsl:otherwise>
</xsl:choose>
</xsl:template>

get-ns-name

Return the namespace name associated to the given prefix. This is functionally equivalent to the fn:namespace-uri-for-prefix function in XPath 2.0. The main difference is that this template does the lookup against the namespace definitions that are in effect in the current context, whereas the XPath 2.0 function allows the element which is used as context to be passed in as argument.
<!-- get the namespace uri for the namespace identified by the prefix in the parameter -->
<xsl:template name="get-ns-name">
<xsl:param name="ns-prefix"/>
<xsl:variable name="ns-node" select="namespace::node()[local-name()=$ns-prefix]"/>
<xsl:value-of select="$ns-node"/>
</xsl:template>

get-ns-prefix

Return a prefix that can be used to denote the given namespace name. This template is complementary to the get-ns-name template. This template assumes only one prefix will be defined for each namespace. The namspace is resolved against the current context.
<!-- get the namespace prefix for the namespace name parameter -->
<xsl:template name="get-ns-prefix">
<xsl:param name="ns-name"/>
<xsl:variable name="ns-node" select="namespace::node()[.=$ns-name]"/>
<xsl:value-of select="local-name($ns-node)"/>
</xsl:template>

resolve-ns-identifier

Return the namespace name for a given QName prefix (be it a namespace prefix or a namspace name). This template is useful to generically obtain a namespace name when feeding it the prefix part of a QName. If the prefix happens to be a namespace name, then that is returned, but if it happens to be a namespace prefix, then a lookup is performed to return the namspace name. This template also looks at the namspaces in effect in the current context.
<!-- return the namespace name -->
<xsl:template name="resolve-ns-identifier">
<xsl:param name="ns-identifier"/>
<xsl:choose>
<xsl:when test="namespace::node()[.=$ns-identifier]">
<xsl:value-of select="$ns-identifier"/>
</xsl:when>
<xsl:when test="namespace::node()[local-name()=$ns-identifier]">
<xsl:value-of select="namespace::node()[local-name()=$ns-identifier]"/>
</xsl:when>
<xsl:otherwise>
<xsl:message terminate="yes">
Error: "<xsl:value-of select="$ns-identifier"/>" is neither a valid namespace prefix nor a valid namespace name.
</xsl:message>
</xsl:otherwise>
</xsl:choose>
</xsl:template>

1 comment:

JP @ logging in Java said...

good post, thanks for sharing information.