XSLT: Extract a Branch from an XML Tree

Often you may wish to extract a portion of an XML file including all of its children elements so as to better deal with it or further transform or handle it elsewhere. 

For example, in web-service-based development, it is common for a developer to “extract” the payload from a request or response envelope.  This can also be in situations where a NIEM developer wishes to obtain the payload portion of a LEXS package and further process, store or display it. 

With XSLT, it only takes the following few lines of code to pull a branch of XML out of a larger package.

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    version="1.0">
    <xsl:output method="xml" indent="yes"/>
    
    <xsl:template match="/uml">
        <xsl:apply-templates select="XMI" mode="RecursiveDeepCopy" />
    </xsl:template> 
    
    <xsl:template match="@*|node()" mode="RecursiveDeepCopy">
        <xsl:copy>
            <xsl:copy-of select="@*" />
            <xsl:apply-templates mode="RecursiveDeepCopy" />
        </xsl:copy> 
    </xsl:template> 

</xsl:stylesheet>

In the above example, the XMI/* elements and attributes are being extracted from the /uml/ container element. Before the transform, the XML would look something like this:

<uml>
  <XMI>
    <XMI.header/>
    <XMI.content/>
  </XMI>
</uml>

And after it would look like this:

<XMI>
  <XMI.header/>
  <XMI.content/>
</XMI>

For information on similar transforms, simply Google or Bing "Identity transforms."