Re: [xsl] keys and idrefs

[Wendell Piez <wapiez at mulberrytech dot com>]

Hi Dave,

Using keys,

>With XML such as
>  <process id="schemaDesign" layer="datalayer" control="XAG
>systemArchitecture" input="systemSpec ">
>     <name>Schema Design</name>
>       </process>
>
>and lots of similar,
>
>then lots of <document elements>
>
>    <document id="XAG" layer="WAI" >
>         <name>XML Guidelines</name>
>       </document>
>
>
>I.e. the idrefs (control attribute on <process>) point to the controlling
>documents.
>
>I'm trying to present the list of processes controlled by the document in an
>html para.

So you want process elements back, using @control:

<xsl:key name="processes-by-control" match="process" use="@control"/>

High-level aside: I think the hardest thing about using a key is getting 
the right key defined, and I find the easiest way to define the right key 
is to find a name for it that describes what it is (hey I'm a poet not a 
mathematician). I also find the English preposition "by" to be very useful 
here because it encapsulates how key relationships work -- you're getting 
something back by means of something else related to it. The something you 
get back is the match pattern; the something else you're using is the use 
expression. So my key names are commonly "x-by-y" where x is the pattern, y 
is the use expression. Makes it easier to think through (and to understand 
the code).

>in the template for 'document' I'm using the hack
>
>   <xsl:template match="document">
>       <xsl:variable name="thisDoc" select="@id"/>
>.....
>  <p> Controls:
>               <xsl:for-each
>select="id(//process|//document[@control='$thisDoc'])">
>                 <a href="{@id}.html"> <xsl:value-of select="name"/>
></a>&#160;
>               </xsl:for-each>
>             </p>

So you'd have
<xsl:for-each select="key('processes-by-control', @id)"> ...

to get back all process elements whose @control attribute is the same as 
the @id attribute of the context node.

But I'm a bit confused by your expression 
"id(//process|//document[@control='$thisDoc'])". This reads to me as though 
you'll get all elements whose attribute of type ID is the same as the 
*content* of any <process> element or of any <document> element with 
@control = '$thisdoc' (the string, not the variable) ... stressing 
"content" because a node-set argument to the id() function acts as though 
giving it a set of strings. I don't think this'll work.

Since you want <process> elements back and @control on each process is an 
IDREF, not an ID, I think you have to use keys; the id() function only goes 
the other way.

If I'm not reading the requirement right, more clarification?

Cheers,
Wendell


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Wendell Piez                            mailto:wapiez@mulberrytech.com
Mulberry Technologies, Inc.                http://www.mulberrytech.com
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