best-technique for selective group and merge?

Given input of the form

  <?xml version="1.0"?>
  <config_datastore>
    <feature name="a">
      <config id="1">
        <param id="x">x</param>
      </config>
    </feature>
    <feature name="b">
      <config id="1">
        <param id="y">y</param>
      </config>
    </feature>
    <feature name="c">
      <config id="1">
        <param id="z">z</param>
      </config>
    </feature>
    <site>
      <has_feature name="a"/>
      <has_feature name="c"/>
    </site>
  </config_datastore>

I want to be able to select /config_datastore/site/* and perform selective
grouping (on feature @name) and merging (on the feature/config elements)
to return:

  <config id="1">
    <param id="x">x</param>
    <param id="z">z</param>
  </config>

Naturally the has_feature elements under site may contain different @name
values (i.e., it won't always be 'a' and 'c').  My immediate thought
was that I could use nested for-each loops and key lookups to resolve
the config elements I am interested in:

  <?xml version="1.0" encoding="iso-8859-1"?>
  <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">       
    <xsl:key name="feature" match="feature" use="@name"/>
  
    <xsl:template match="/">
      <xsl:variable name="tree_fragment">
        <xsl:for-each select="/config_datastore/site/has_feature">
          <xsl:for-each select="key('feature', @name)/config">
            <xsl:copy-of select="."/>
          </xsl:for-each>
        </xsl:for-each>
      </xsl:variable>
      <!-- need to then merge $tree_fragment/config elements -->
      <!-- perhaps using node-set conversion -->
    </xsl:template>
  </xsl:stylesheet>

This leaves me with a rather unhelpful tree-fragment of the form

  <config id="1">
    <param id="x">x</param>
  </config>
  <config id="1">
    <param id="z">z</param>
  </config>
 
In order to then merge the two config elements, I'd need ot pass
$tree_fragment through some non-XSLT-1.0 compliant function to get
a node-set which I could further manipulate.

Two questions:

  a) Is it considered fine w/re to "programming form" to use
     these node-set transformations, given that we will get
     them in XSLT 2.0?
  
  b) Is there another way, using pure XSLT 1.0 functionality,
     to perform the selective group and merge?  I have vague
     inklings of recursive scans of /feature/config inside
     the processing of has_feature, but that seems as ugly as
     my recursive counter post a few days ago (i.e., perhaps
     flexible and 1.0 compliant, but ugly and slow).

Any insights would be appreciated!


Thank you for your time,

Jim

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James A. Robinson                       jimr@xxxxxxxxxxxxxxxxxxxxx
Stanford University HighWire Press      http://highwire.stanford.edu/
650-723-7294 (W) 650-725-9335 (F)   

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