[xsl] SGML Inclusions and infinitive recursion (in XSLT)

Just when you thought you'd never answer another question about SGML 
inclusions. . .

I'm working with the XML files produced by Norm Walsh's tool DTDParse. These 
files represent an SGML or XML DTD. In my case, it's SGML DTDs.

I've written a transformation that produces an HTML view of the DTD. It's quite 
handy, but there's one thing I can't quite get to work and I really need to 
resolve this issue: inclusions.

Here's a snippet of the kind of output in the XML file I'm working with:

<dtd>

 <element name="HEAD" stagm="O" etagm="O" content-type="element">
  <content-model-expanded>
   <and-group>
    <element-name name="TITLE"/>
    <element-name name="ISINDEX" occurrence="?"/>
    <element-name name="BASE" occurrence="?"/>
   </and-group>
  </content-model-expanded>
  <content-model>
   <sequence-group>
    <parament-name name="head.content"/>
   </sequence-group>
  </content-model>
  <inclusions>
   <or-group>
    <element-name name="SCRIPT"/>
    <element-name name="STYLE"/>
    <element-name name="META"/>
    <element-name name="LINK"/>
    <element-name name="OBJECT"/>
   </or-group>
  </inclusions>
 </element>
 <!-- one such element for every element declared in the DTD -->
</dtd>

What I want to do is produce, for every element, not only what it's declared 
content model is (in DTDParse's output file, the content of 
<content-model-expanded>), but also of any inclusions that apply to the 
element. And that's where the problem is.

If I recall SGML inclusions correctly, an inclusion declared on an element 
applies to all child elements all the way to the bottom of the relevant part of 
the document tree.

As I understand it, what I need to do is find the parent element(s) of a given 
element, and see if they have any inclusions; if so, output them. Then, find 
the parents of that element (or elements) and do the same. And so on. So far 
I've only done this using <xsl:for-each> and simply moved from one element to 
its parent(s) and so on:

<xsl:template name="trace_ancestor_inclusions">
 <xsl:param name="element_name" />
  <!-- this changes the context to each parent element of the original element 
-->
  <xsl:for-each 
select="parent::dtd/element[content-model-expanded/descendant::element-name[(_at_)name=$element_name]]">
  <xsl:variable name="new_element_name" select="@name" />
    <p style="padding-left: 20px;">Ancestor Element: <xsl:value-of 
select="$new_element_name"/><xsl:text> </xsl:text>
      <xsl:for-each select="inclusions/*">                              
        <xsl:text>( </xsl:text><xsl:apply-templates select="." /><xsl:text> 
)</xsl:text>
      </xsl:for-each>
    </p>        
   <xsl:call-template name="trace_ancestor_inclusions">
     <xsl:with-param name="element_name" select="$new_element_name" />
   </xsl:call-template>                 
  </xsl:for-each>                       
</xsl:template>

It seems that what I need is a test around the call-template at the end of the 
template to test whether I've already encountered a given element and bypass 
it. If someone could show me what that logic would be, I would be most 
appreciative.

Thanks,

Don


      

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