Two/multi phases XSLT processing

Two/multi phases XSLT is very useful if you do have multiple steps to process your data. Here is an example.

I have a data dictionary to store authors:

<?xml version="1.0" encoding="UTF-8"?>
<authors>
  <author>Wyatt, T.</author>
  <author>Smith, A.</author>
  <author>Davids, D.</author>
</authors>

Everytime when I've got a new XML document, I need to check a particular element (fullName) to update data dictionary file. The XML document looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<doc>
  <creator>
    <fullName>Wyatt, A.</fullName>
  </creator>
  ...
</doc>

While updating data dictionary, I need to make sure there is no duplicate getting into data dictionary.

Multi-phase processing can be used to do this job. The key point for multiphase processing is to store the previous processing result into a variable and use that variable as the initial XML to process in the later phase. The example XSLT is shown below:

<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
      exclude-result-prefixes="xsl">
  <xsl:strip-space elements="*"/>
  <xsl:output method="xml" indent="yes"/>

  <xsl:variable name="authorsDoc" select="document('authors.xml', /)"/>

  <xsl:template match="/">
    
    <xsl:variable name="phase-1-output">
      <authors>
        
        <xsl:for-each select="/doc/creator/fullName[.!='']">
            <xsl:variable name="currentName" select=".[.=$authorsDoc//author]"/>
            <xsl:if test="not($currentName)">
              <author><xsl:value-of select="."/></author>
            </xsl:if>
        </xsl:for-each>

        
        <xsl:for-each select="$authorsDoc/authors/author[.!='']">
          <xsl:sort select="."/>
          <author><xsl:value-of select="."/></author>
        </xsl:for-each>
      </authors>
    </xsl:variable>

   
    <authors>
      <xsl:for-each select="$phase-1-output/authors/author[.!='' and (not(.=preceding-sibling::author))]">     
        <xsl:sort select="."/>
        <author><xsl:value-of select="."/></author>
      </xsl:for-each>
    </authors>

  </xsl:template>

</xsl:stylesheet>