XSLT identity transform produces wrong namespace - xslt

Question

I have a custom XML schema that is evolving: elements are added, others deleted, and the namespace changes to reflect the new version (e.g., from "http://foo/1.0" to "http://foo/1.1"). I want to write an XSLT that converts XML documents from the old schema to the new one. My first attempt works, but it's verbose and unscalable, and I need help refining it.
Here's a sample document for the 1.0 schema:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<foo:rootElement xmlns:foo="http://foo/1.0">
<obsolete>something</obsolete>
<stuff>
<alpha>a</alpha>
<beta>b</beta>
</stuff>
</foo:rootElement>
In the 1.1 schema, the "obsolete" element goes away but everything else remains. So the XSLT needs to do two things:
Remove the tag
Change the namespace from http://foo/1.0 to http://foo/1.1
Here's my solution:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:foo1="http://foo/1.0"
xmlns:foo="http://foo/1.1"
exclude-result-prefixes="foo1">
<xsl:output method="xml" standalone="yes" indent="yes"/>
<!-- Remove the "obsolete" tag -->
<xsl:template match="foo1:rootElement/obsolete"/>
<!-- Copy the "alpha" tag -->
<xsl:template match="foo1:rootElement/stuff/alpha">
<alpha>
<xsl:apply-templates/>
</alpha>
</xsl:template>
<!-- Copy the "beta" tag -->
<xsl:template match="foo1:rootElement/stuff/beta">
<beta>
<xsl:apply-templates/>
</beta>
</xsl:template>
<!-- Copy the "stuff" tag -->
<xsl:template match="foo1:rootElement/stuff">
<stuff>
<xsl:apply-templates/>
</stuff>
</xsl:template>
<!-- Copy the "rootElement" tag -->
<xsl:template match="foo1:rootElement">
<foo:rootElement>
<xsl:apply-templates/>
</foo:rootElement>
</xsl:template>
</xsl:stylesheet>
Although this produces the output I want, notice that I have a copying template for every element in the schema: alpha, beta, etc. For complex schemas with hundreds of kinds of elements, I'd have to add hundreds of templates!
I thought I could eliminate this problem by reducing all those copying templates into a single identity transform, like this:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:foo1="http://foo/1.0"
xmlns:foo="http://foo/1.1"
exclude-result-prefixes="foo1">
<xsl:output method="xml" standalone="yes" indent="yes"/>
<xsl:template match="foo1:rootElement/obsolete"/>
<xsl:template match="node()|#*" name="identity">
<xsl:copy>
<xsl:apply-templates select="node()|#*"/>
</xsl:copy>
</xsl:template>
<xsl:template match="foo1:rootElement/stuff">
<xsl:copy>
<xsl:call-template name="identity"/>
</xsl:copy>
</xsl:template>
<xsl:template match="foo1:rootElement">
<foo:rootElement>
<xsl:apply-templates/>
</foo:rootElement>
</xsl:template>
</xsl:stylesheet>
But it produces:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<foo:rootElement xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:foo="http://foo/1.1">
<stuff xmlns:foo="http://foo/1.0">
<stuff>
<alpha>a</alpha>
<beta>b</beta>
</stuff>
</stuff>
</foo:rootElement>
The "stuff" element was copied, which is what I want, but it's wrapped in another "stuff" element, tagged with the old namespace. I don't understand why this is happening. I've tried many ways of fixing this but have been unsuccessful. Any suggestions? Thanks.

Answer 1

This transformation:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:param name="pOldNS" select="'http://foo/1.0'"/>
<xsl:param name="pNewNS" select="'http://foo/1.1'"/>
<xsl:template match="/*">
<xsl:element name="{name()}" namespace="{$pNewNS}">
<xsl:apply-templates select="node()|#*"/>
</xsl:element>
</xsl:template>
<xsl:template match="*">
<xsl:element name="{name()}">
<xsl:copy-of select="namespace::*[not(.=$pOldNS)]"/>
<xsl:apply-templates select="node()|#*"/>
</xsl:element>
</xsl:template>
<xsl:template match="#*">
<xsl:choose>
<xsl:when test="namespace-uri()=$pOldNS">
<xsl:attribute name="{name()}" namespace="{$pNewNS}">
<xsl:value-of select="."/>
</xsl:attribute>
</xsl:when>
<xsl:otherwise>
<xsl:copy-of select="."/>
</xsl:otherwise>
</xsl:choose>
</xsl:template>
<xsl:template match="obsolete"/>
</xsl:stylesheet>
when applied on this XML document:
<foo:rootElement xmlns:foo="http://foo/1.0">
<obsolete>something</obsolete>
<stuff>
<alpha x="y" foo:t="z">a</alpha>
<beta>b</beta>
</stuff>
</foo:rootElement>
produces the wanted, correct result (obsolute elements deleted, namespace upgraded, attribute nodes correctly processed, including nodes that were in the old namespace):
<foo:rootElement xmlns:foo="http://foo/1.1">
<stuff>
<alpha x="y" foo:t="z">a</alpha>
<beta>b</beta>
</stuff>
</foo:rootElement>
Main advantages of this solution:
Works correctly when there are attributes, belonging to the old-schema namespace.
General, allows the old and new namespace to be passed as external parameters to the transformation.

Answer 2

While you might want to copy the attributes, elements need to be regenerated in the new namespace. So I'd suggest to do it like this:
<xsl:stylesheet version="2.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:foo1="http://foo/1.0">
<xsl:template match="foo1:rootElement/obsolete"/>
<xsl:template match="attribute()">
<xsl:copy/>
</xsl:template>
<xsl:template match="element()">
<xsl:variable name="name" select="local-name()"/>
<xsl:element name="{$name}" namespace="http://foo/1.1">
<xsl:apply-templates select="node()|#*"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>