XSLT to replace a namespace and also add a new (unused) namespace - xslt

Question

I want to replace the namespace of the following XML Document
<?xml version="1.0" encoding="UTF-8"?>
<ns0:Document xmlns:ns0="http://mydata.com/H2H/Automation">
<CstmrCdtTrfInitn>
<GrpHdr>
</GrpHdr>
</CstmrCdtTrfInitn>
</ns0:Document>
with the following
<?xml version="1.0" encoding="UTF-8"?>
<Document xmlns="urn:iso:std:iso"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<CstmrCdtTrfInitn>
<GrpHdr>
</GrpHdr>
</CstmrCdtTrfInitn>
</Document>
Any idea about XSLT which can convert this?
I have tried the following XSL, but it is adding the namespace with second Node and also not able to remove first namespace.
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output encoding="UTF-8" indent="yes"/>
<xsl:template match="/*">
<xsl:element name="{local-name()}" namespace="http://www.w3.org/2001/XMLSchema-instance">
<xsl:copy-of select="./*" />
</xsl:element>
</xsl:template>
</xsl:stylesheet>

Answer 1

Your requirement can be a bit tricky: replacing the default namespace of the Document element is straightforward. But adding the unused xslns:xsi namespace in XSLT-1.0 requires the EXSLT extension and a special technique explained by Michael Kay in reply to this question. It involves creating an unused element in a global variable whose namespace is then copied in the template replacing the default namespace. In XSLT-2.0 and above this would be easier (see below).
The EXSLT extension is not available in all XSLT-1.0 processors. But it is necessary to create a node-set from the variable.
So all namespaces are to be defined in the xsl:stylesheet element, and then the root element (here ns0:Document) is matched by a template and replaced with its local-name() part with the new default namespace added, followed by copying the "dummy" namespace of the element defined in the variable.
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:ns0="http://mydata.com/H2H/Automation" xmlns:urn="urn:iso:std:iso" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:ext="http://exslt.org/common">
<xsl:output method="xml" omit-xml-declaration="yes" indent="yes"/>
<!-- identity template (except elements)-->
<xsl:template match="node()[not(self::*)]|#*">
<xsl:copy>
<xsl:apply-templates select="node()|#*" />
</xsl:copy>
</xsl:template>
<xsl:variable name="nsXSI">
<xsl:element name="xsi:dummy" namespace="http://www.w3.org/2001/XMLSchema-instance" />
</xsl:variable>
<xsl:template match="ns0:*|*">
<xsl:element name="{local-name()}" namespace="urn:iso:std:iso">
<xsl:copy-of select="ext:node-set($nsXSI)/*/namespace::xsi" />
<xsl:apply-templates select="node() | #*" />
</xsl:element>
</xsl:template>
</xsl:stylesheet>
Output should be as expected, even in XSLT-1.0:
<Document xmlns="urn:iso:std:iso" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<CstmrCdtTrfInitn>
<GrpHdr>
</GrpHdr>
</CstmrCdtTrfInitn>
</Document>
The simplified solution requires an XSLT-2.0 capable processor. Then you can use the xsl:namespace instruction as follows and don't need the "dummy" variable:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:ns0="http://mydata.com/H2H/Automation">
<xsl:output method="xml" omit-xml-declaration="yes" indent="yes"/>
<!-- identity template (except elements)-->
<xsl:template match="node()[not(self::element())]|#*">
<xsl:copy>
<xsl:apply-templates select="node()|#*" />
</xsl:copy>
</xsl:template>
<xsl:template match="ns0:*|*">
<xsl:element name="{local-name(.)}" namespace="urn:iso:std:iso">
<xsl:namespace name="xsi">http://www.w3.org/2001/XMLSchema-instance</xsl:namespace>
<xsl:apply-templates select="node() | #*" />
</xsl:element>
</xsl:template>
</xsl:stylesheet>
The output is the same.
The above XSLT-2.0 solution could be further simplified by using XSLT-3.0+'s xsl:mode to replace the identity template with
<xsl:mode on-no-match="shallow-copy"/>

Answer 2

Is there a reason why you cannot do simply:
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:ns0="http://mydata.com/H2H/Automation"
exclude-result-prefixes="ns0">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="*">
<xsl:element name="{local-name()}" namespace="urn:iso:std:iso">
<xsl:apply-templates/>
</xsl:element>
</xsl:template>
<xsl:template match="/ns0:Document">
<Document xmlns="urn:iso:std:iso" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<xsl:apply-templates/>
</Document>
</xsl:template>
</xsl:stylesheet>