Question

I am wondering whether XSLT makes it possible to sort an XML file if I don’t know the entire XML-schema.

For example I would like to sort the following XML file.
Sort /CATALOG/CD elements by /CATALOG/CD/TITLE

<CATALOG attrib1="value1">
  <DVD2>
    <TITLE>The Godfather2</TITLE>
  </DVD2>
  <CD>
    <TITLE>Hide your heart</TITLE>
    <ARTIST>Bonnie Tyler</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>CBS Records</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1988</YEAR>
  </CD>
  <CD attrib4="value4">
    <TITLE>Empire Burlesque</TITLE>
    <ARTIST>Bob Dylan</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Columbia</COMPANY>
    <PRICE>
      <CATALOG>
        <CD><TITLE>E</TITLE></CD>
        <CD><TITLE>I</TITLE></CD>
        <CD><TITLE>D</TITLE></CD>
      </CATALOG>
    </PRICE>
    <YEAR>1985</YEAR>
  </CD>
  <CD attrib2="value2">
    <TITLE attrib3="value3">Greatest Hits</TITLE>
    <ARTIST>Dolly Parton</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>RCA</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1982</YEAR>
  </CD>
  <DVD>
    <TITLE>The Godfather1</TITLE>
  </DVD>
</CATALOG>

The output should be:

<CATALOG attrib1="value1">
  <CD attrib4="value4">
    <TITLE>Empire Burlesque</TITLE>
    <ARTIST>Bob Dylan</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Columbia</COMPANY>
    <PRICE>
      <CATALOG>
        <CD><TITLE>E</TITLE></CD>
        <CD><TITLE>I</TITLE></CD>
        <CD><TITLE>D</TITLE></CD>
      </CATALOG>
    </PRICE>
    <YEAR>1985</YEAR>
  </CD>
  <CD attrib2="value2">
    <TITLE attrib3="value3">Greatest Hits</TITLE>
    <ARTIST>Dolly Parton</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>RCA</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1982</YEAR>
  </CD>
  <CD>
    <TITLE>Hide your heart</TITLE>
    <ARTIST>Bonnie Tyler</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>CBS Records</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1988</YEAR>
  </CD>
  <DVD2>
    <TITLE>The Godfather2</TITLE>
  </DVD2>
  <DVD>
    <TITLE>The Godfather1</TITLE>
  </DVD>
</CATALOG>

The following is one of the many tries I did:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/">
    <!--<CATALOG>-->
    <xsl:for-each select="CATALOG/CD">
      <xsl:sort select="TITLE" />
      <xsl:copy-of select="."/>
    </xsl:for-each>
    <!--</CATALOG>-->
  </xsl:template>
</xsl:stylesheet>

The problem is that, with this XSLT, XML parts outside the CD list are not displayed.
I could uncomment the two commented-out parts of code, but that’s exactly what I want to avoid.
In that case if any attributes are added to the CATALOG element, they would not be copied to output XML.
I don’t want to re-build the XML file: I just want to do a sort knowing exact information only about some part of the XML-schema.

This functionality is easy to implement for example using .NET (with XmlDocument and XmlNode objects), or Python’s lxmx library, but is it possible with XSLT?

Thanks!

Note: It is not easy to find a sample input XML which will avoid misunderstanding the question in all cases. But I will try to detail the problem as much as I can:

• only CD elements right under CATALOG should be sorted (for example CD elements under the Bob Dylan section should be left untouched)
• it is all the same whether elements other than CD (for example DVD and DVD2) are in the beginning or end of the list
• no elements, attributes, values, comments, so nothing should be missing from the output XML
• non-CD elements (for example DVD and DVD2) should not be sorted by the TITLE subelement

Answer 1

Keeping on the line of just modifying the identity transformation (which might not be really safe), I think that the following should be equivalent to @Tim’s answer.

NOTE I’m not promoting this technique at all, unless you understand what’s the general behavior of the identity transformation.

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:template match="@* | node()">
        <xsl:copy>
            <xsl:apply-templates select="@* 
                | node()[not(self::CD[parent::CATALOG])]"/>
            <xsl:apply-templates select="CD[parent::CATALOG]">
                <xsl:sort select="TITLE"/>
            </xsl:apply-templates>
        </xsl:copy>
    </xsl:template>

</xsl:stylesheet>

or, if you care about the other elements DVD and DVD2, you can do:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:template match="@* | node()">
        <xsl:copy>
            <xsl:apply-templates select="@*"/>
            <xsl:apply-templates select="CD[parent::CATALOG]">
                <xsl:sort select="TITLE"/>
            </xsl:apply-templates>
            <xsl:apply-templates select="node()
                [not(self::CD[parent::CATALOG])]"/>
        </xsl:copy>
    </xsl:template>

</xsl:stylesheet>