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Re: Getting a predicate right

Subject: Re: Getting a predicate right
From: "G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>
Date: Tue, 30 Jul 2002 15:51:38 -0400
xpath nested predicate
At 2002-07-30 12:25 -0700, Kuhns Matt wrote:
My XML Sheet looks like this:
...
In my XSL I am going through the messages and trying
to match the attribute grp from mesg with the
attribute id from desc.

I think you should be using keys for this ... an example is below. I load a key table named "colours" with "desc" elements keyed by their "id" attribute. I then look up the needed "desc" element using the key() function and determine the value of the "name" attribute attached to the element found.


something like this:
//test/colors/desc[@grp]/@name
or
//test/colors/desc[@id = @grp]/@name

You are comparing the id attribute of desc with the grp attribute of desc, which is why you are not getting what you want.


Note also that using "//" is *very* wasteful. Often the performance of many stylesheets is optimized by finding and eliminating any use of "//". Many users of XPath don't realize that looking for "//x" will find all "x" elements and then continue looking inside those elements for more "x" elements that might be nested. Using "//x" will search *every* "x" element node down to the leaves of the node tree, which can take a long time for the tree of a big instance.

I hope this helps.

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

T:\ftemp>type matt.xml
<test>
<colors>
  <desc id="0" name="blue"/>
  <desc id="1" name="red"/>
  <desc id="2" name="white"/>
</colors>
<mesg grp="1">Hi how are you?</mesg>
<mesg grp="0">I am fine.</mesg>
<mesg grp="2">That is good.</mesg>
</test>

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

<xsl:key name="colours" match="desc" use="@id"/>

<xsl:output indent="yes"/>

<xsl:template match="/">
  <xsl:for-each select="/test/mesg">
    <p color="{key('colours',@grp)/@name}"><xsl:apply-templates/></p>
  </xsl:for-each>
</xsl:template>

</xsl:stylesheet>

T:\ftemp>saxon -o matt.out matt.xml matt.xsl

T:\ftemp>type matt.out
<?xml version="1.0" encoding="utf-8"?>
<p color="red">Hi how are you?</p>
<p color="blue">I am fine.</p>
<p color="white">That is good.</p>
T:\ftemp>


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G. Ken Holman                 mailto:gkholman@xxxxxxxxxxxxxxxxxxxx
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