[xsl] Common Element Solution (XSL 2.0)

[JBryant@xxxxxxxxx]

This is neither a question nor an answer to someone else's question. I had 
to solve a problem today (finding all the common columns in an XML 
representation of a database), and it occurred to me that the solution 
might be useful for others. So, I'm posting for the sake of future archive 
searchers. For several years (since early 2000), I would occasionally need 
an XSL solution and would search the archives for solutions to my 
problems. Now that I use XSL all a lot (was only occasional before), I'm 
trying to give back a bit as my understanding grows.

Of course, if anyone does have comments, I welcome input. I'm sure I'll 
never stop learning (at least I hope not).

Given this XML file:

<?xml version="1.0" encoding="UTF-8"?>
<tables>
  <table name="table1">
    <column name="col1"/>
    <column name="col2"/>
    <column name="col3"/>
    <column name="col4"/>
  </table>
  <table name="table2">
    <column name="col1"/>
    <column name="col2"/>
    <column name="col5"/>
    <column name="col6"/>
  </table>
  <table name="table3">
    <column name="col1"/>
    <column name="col2"/>
    <column name="col7"/>
    <column name="col8"/>
  </table> 
</tables>

Find the columns shared by all tables, by column name.

The solution (in XSL 2.0):

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="2.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform";>

  <xsl:template match="/">
    <commonColumns>
      <xsl:apply-templates/>
    </commonColumns>
  </xsl:template>

  <xsl:template match="tables">
    <xsl:for-each-group select="table/column" group-by="@name">
      <xsl:variable name="name" select="@name"/>
      <xsl:if 
test="count(/tables/table/column[@name=$name])=count(/tables/table)">
        <columnName><xsl:value-of select="@name"/></columnName>
      </xsl:if>
    </xsl:for-each-group>
  </xsl:template>

</xsl:stylesheet>

Produces the following output with Saxon 8:

<?xml version="1.0" encoding="UTF-8"?>
<commonColumns>
  <columnName>col1</columnName>
  <columnName>col2</columnName>
</commonColumns>

FWIW

Jay Bryant
Bryant Communication Services
(presently consulting at Synergistic Solution Technologies)