Re: [xsl] Pattern Matching in XSl - find groups defined in one Xml in another Xml.

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Dear Richard,

Ken has actually demonstrated everything you need to know in the problem 
you pose. Indeed, since the difference between his solution 1 and 
solution 2 is effectively the matching criterion -- what qualifies an 
entry as "found" -- then comparing the two should show you what you need 
to generalize to any matching criteria you may have (comparing two or 
more values, etc.).

It's true that in giving you complete solutions, he hasn't separated the 
solution to the problem as posed from the incidentals that go with 
making it work. But this makes good homework. (By not breaking it down 
and explaining it he's actually expressing his confidence in you, I'd 
say.) So I suggest taking the next step by picking one of his solutions 
and tinkering with it. (Undoubtedly you are already doing this.) Do feel 
free while you are doing so to come back to the list with more questions.

If it were my problem I might encapsulate the test for a match into a 
stylesheet function, both for clarity and maintenance. A first step 
could be to do this with Ken's solution 1, something like

<xsl:function name="x:my-group" as="element(group)*">
  <!-- returns any 'group' elements in groups.xml with child
       nodes matching $me/@equipment by the 'grouped' key -->
  <xsl:param name="me" as="element(alarm)"/>
  <xsl:sequence
    select="key('grouped',$me/@equipment,doc('groups.xml'))
            /parent::group"/>
</xsl:function>

(I did make a slight change from Ken's logic: this fetches the 'group' 
element not the 'alarm' element inside it.)

then

<xsl:template match="alarm">
  <xsl:copy>
    <xsl:apply-templates select="@*"/>
    <xsl:for-each select="x:my-group(.)">
      <xsl:attribute name="found" select="@id"/>
    </xsl:for-each>
  </xsl:copy>
</xsl:template>

Once the logic is embedded in the function you can extend or refine it 
as much as you like. Nor do you have to use a key, as Ken did (and then 
didn't in his second solution): what the function does is return the 
elements from your lookup document that correspond with the 'alarm' 
element being matched, and any way it does that is fine.

Cheers,
Wendell

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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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