Re: [xsl] Need to output an opening or closing tag by itself

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

David,

> <xsl:template match="e">
>   <xsl:choose>
>     <xsl:when test="@t ='a'">
>       <e>
>     </xsl:when>
>     <xsl:when test="@t ='b'">
>       </e>
>     </xsl:when>
>     <xsl:otherwise>
>       <xsl:message terminate="yes">
>         Unexpected data in attribute t.
>       </xsl:message>
>     </xsl:otherwise>
>   </xsl:choose>
> </xsl:template>

Even if it worked (the code is syntactically broken), this approach 
constitutes "tag-writing", and won't work in XSLT for reasons others 
will explain (or have done so). XSLT doesn't work with tags; it works 
on a tree of nodes derived from the tagging of the input: elements, 
attributes and text arranged in a hierarchy, and it builds the same 
kind of tree.

Your problem is properly approached, in XSLT, as a grouping problem. 
The nodes between the 'e' elements must be grouped together.

As such, it infers a structure that is only implicit in the original 
data, and thus qualifies as an "upconversion" (a transformation that 
adds information). Accordingly, it isn't going to be easy without 
using features designed for this purpose. Most of these make an 
appearance only in XSLT 2.0, although techniques have been devised in 
XSLT 1.0 to accomplish it (such as sibling recursion or structural 
induction using keys to associate the groups).

If you really want to use a tag-writing approach to transformation, 
even in XSLT, that can be done, but (a) experience has shown that 
past trivial cases it's generally much more work than the orthodox 
method (indeed, much of this experience was won in the 1990s and 
earlier, before XSLT even existed), and (b) it introduces an 
architectural dependency. Specifically, the output must be written as 
a file, something that is not necessary in many XML processing 
architectures for which XSLT is well suited.

Cheers,
Wendell



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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
Mulberry Technologies, Inc.                http://www.mulberrytech.com
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Suite 207                                          Phone: 301/315-9631
Rockville, MD  20850                                 Fax: 301/315-8285
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