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lookup table (was: mixed content nodes question)

2005-01-07 15:44:44
Michael Kay writes:
Or to one who doesn't like if's

<xsl:template match="dictionary[lookup = '3']>Foo<xsl:/template>
<xsl:template match="dictionary[lookup = '4']>Foo<xsl:/template>

My preferred way to do lookups is to make it table driven:

<xsl:variable name="table">
  <entry code="3" value="foo"/>
  <entry code="4" value="bar"/>
</xsl:variable>

<xsl:template match="dictionary">
  <xsl:value-of select="$table/entry[(_at_)code=current()/@lookup]/@value"/>
</xsl:template>

I'm a novice working on my first stylesheet, which has a lookup table
that I implemented like this:

<xsl:template name="convert-language">
  <xsl:param name="code">en</xsl:param>
  <!-- See ISO 639 -->
  <xsl:choose>
    <xsl:when test="$code = 'ar'">ARABIC</xsl:when>
    <xsl:when test="$code = 'de'">GERMAN</xsl:when>
    <xsl:when test="$code = 'es'">SPANISH</xsl:when>
...
    <xsl:otherwise>
      <xsl:message terminate="no">Unrecognized language code: <xsl:value-of 
select="$code"/></xsl:message>
      <xsl:value-of select="$code"/>
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>

That is accessed like this:

      <xsl:call-template name="convert-language">
        <xsl:with-param name="code"
           select="stringmb3e:doc_lang_list/mb3e:doc_lang[1]"/>
      </xsl:call-template>

Then I came across an element that had no mb3e:doc_lang_list child and
thus no mb3e:doc_lang grandchildren, which generated the "Unrecognized
language code" message (with no value for the allegedly erroneous code).
So I added this instruction before <xsl:otherwise> to simply return an
empty string in that case:

    <xsl:when test="$code = ''"></xsl:when>

I was surprised that (under Xalan 2.6.0) that didn't solve the problem
-- I still got the error message.  I got the desired behavior by
changing the call to this:

      <xsl:call-template name="convert-language">
        <xsl:with-param name="code"
           select="string(mb3e:doc_lang_list/mb3e:doc_lang[1])"/>
      </xsl:call-template>

But I obviously have a fundamental misunderstanding: I know that the
select expression in the original call returns a node-set, which the
XSLT processor apparently converts automatically to a string when
evaluating the test expression (as desired, since I get the intended
language names in my output).  So why doesn't the empty node-set match
the empty string test (i.e. why do I have to explicitly convert it
before calling the lookup template)?

Needs the xx:node-set() extension or the document("") cheat if using XSLT
1.0.

I'd rather learn the ropes and get an XSLT 1.0 prototype working before
delving into XSLT 2.0.  What are the advantages of your implementation,
and what are the xx:node-set() extension and the document("") cheat?

Thanks,
-- 
Kevin Rodgers


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