Re: [xsl] Generic Lookup (Element Mapping)

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

At 2002-05-07 08:15 -0500, Faroukh Fekravar wrote:
> I have been trying to write a generic xslt template to map the element names
> based on a lookup table.

Is there a reason you want to do this in one stylesheet with both the 
mapping file and the data file?

> The lookup xml file has always a subset of the elements and therefore I do
> not want to hard code the element names.

Then you need a customized stylesheet based on your mappings, especially 
for speed in order to do a single pass on the input data.

> The output file is a flat xml file in opposite to the input file.

This was a particularly difficult criterion to meet.

> But my main problem is how navigate through the input file in a generic
> approach.
> I'm also just a little concern about the overall performance because the
> input file might be MBs big.

For performance reasons, I recommend you write a stylesheet that, based on 
your mapping, emits a single stylesheet that is then run against your 
data.  This emitted stylesheet does simple matches and should meet your 
performance requirements.

An example of writing a stylesheet that writes a stylesheet is in Chapter 5 
of "Definitive XSLT and XPath" which happens to be the freely-downloadable 
chapter made available by Prentice Hall on the Amazon site.  It is also in 
Chapter 5 of our electronic book from which the paper book was derived.

A working answer to your requirements is below.

I hope this helps.

...................... Ken


t:\ftemp>type data.xml
<?xml version="1.0" encoding="iso-8859-1"?>
<project>
        <aa1>
                <aa11>aa11_value</aa11>
                <aa12>aa12_value</aa12>
                <aa13>aa13_value</aa13>
                <aa2>
                        <aa21>aa21_value</aa21>
                        <aa22>aa22_value</aa22>
                        <aa3>
                                <aa31>aa31_value</aa31>
                                <aa4>
                                        <aa41>aa41_value</aa41>
                                </aa4>
                        </aa3>
                </aa2>
        </aa1>
</project>

t:\ftemp>type lookup.xml
<?xml version="1.0" encoding="iso-8859-1"?>
<Maps>
        <Map>                                           <!-- combination 
of SEName, SAname and TEname is unique through
the file.-->
                <SEname>aa1</SEname>            <!--  element name in the 
input file-->
                <SAname>aa11</SAname>           <!-- element name in the 
input file, it's always
the child element of SEName-->
                <TEname>aa_1</TEname>           <!-- element name in output-->
                <TAname>aa_11</TAname>          <!-- element nemae in 
output, it should be the
child element of TEname-->
        </Map>
        <Map>
                <SEname>aa1</SEname>
                <SAname>aa12</SAname>
                <TEname>aa_1</TEname>
                <TAname>aa_12</TAname>
        </Map>
        <Map>
                <SEname>aa1</SEname>
                <SAname>aa13</SAname>
                <TEname>aa_1A</TEname>
                <TAname>aa_13</TAname>
        </Map>
        <Map>
                <SEname>aa2</SEname>
                <SAname>aa21</SAname>
                <TEname>aa_2</TEname>
                <TAname>aa_21</TAname>
        </Map>
<!-- no mapping for aa22 -->
        <Map>
                <SEname>aa3</SEname>
                <SAname>aa31</SAname>
                <TEname>aa_3</TEname>
                <TAname>aa_31</TAname>
        </Map>
</Maps>

t:\ftemp>type faroukh.xsl
<?xml version="1.0" encoding="iso-8859-1"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform";
                xmlns:xslo="junk"
                version="1.0">

<xsl:namespace-alias stylesheet-prefix="xslo" result-prefix="xsl"/>

<xsl:key name="parents" match="Map" use="SEname"/>
<xsl:key name="children" match="Map" use="concat(SEname,' ',TEname)"/>

<xsl:template match="/">
  <xslo:stylesheet version="1.0">
    <xslo:output indent="yes"/>
    <xslo:template match="/project"><!--preserve project element-->
      <project>
        <xslo:apply-templates/>
      </project>
    </xslo:template>
    <xslo:template match="*"/><!--throw away unmapped-->
    <xslo:template match="text()"/><!--only keep explicitly copied text-->
    <xsl:apply-templates/>
  </xslo:stylesheet>
</xsl:template>

<xsl:template match="Map">
                           <!--only put out a single template for the 
parent-->
  <xsl:if test="generate-id(.)=generate-id(key('parents',SEname))">
    <xslo:template match="{SEname}">
                 <!--needs as many apply templates as unique parent 
mappings-->
      <xsl:for-each select="key('parents',SEname)[generate-id(.)=
                      generate-id(key('children',concat(SEname,' 
',TEname)))]">
        <xslo:element name="{TEname}">
          <xslo:apply-templates mode="mapping">
            <xsl:attribute name="select">
              <xsl:for-each select="key('children',concat(SEname,' 
',TEname))">
                <xsl:if test="position()>1">|</xsl:if>
                <xsl:value-of select="SAname"/>
              </xsl:for-each>
            </xsl:attribute>
          </xslo:apply-templates>
        </xslo:element>
      </xsl:for-each>
      <xslo:apply-templates/>
    </xslo:template>
  </xsl:if>
  <xslo:template match="{SEname}/{SAname}" mode="mapping">
    <xslo:element name="{TAname}">
      <xslo:value-of select="."/>
    </xslo:element>
  </xslo:template>
</xsl:template>

</xsl:stylesheet>

t:\ftemp>saxon -o mapping.xsl lookup.xml faroukh.xsl

t:\ftemp>saxon -o faroukh.out data.xml mapping.xsl

t:\ftemp>type faroukh.out
<?xml version="1.0" encoding="utf-8"?>
<project>
   <aa_1>
      <aa_11>aa11_value</aa_11>
      <aa_12>aa12_value</aa_12>
   </aa_1>
   <aa_1A>
      <aa_13>aa13_value</aa_13>
   </aa_1A>
   <aa_2>
      <aa_21>aa21_value</aa_21>
   </aa_2>
   <aa_3>
      <aa_31>aa31_value</aa_31>
   </aa_3>
</project>
t:\ftemp>rem Done!


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G. Ken Holman                mailto:gkholman@xxxxxxxxxxxxxxxxxxxx
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