Re: [xsl] Which commands to use: xsl:if, xsl:when, xsl:choose, xsl:otherwise ??

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

At 2004-01-27 10:31 -0800, Bill Walker wrote:
> I have learned just enough XML and XSLT to think I
> understand what I am doing.

Congratulations!

> However, when I am faced with something that takes
> more logic and real understanding of such things as:
>
> xsl:if
>
> xsl:choose
>
> xsl:when
>
> xsl:otherwise
>
> ?I find I really don?t understand how to use them or
> what is going on with the XSLT and the processing?

They are useful *within* a template ... sounds like you just need different 
sets of templates.

> I COULD just go on and
> create an XML and an XSL file for each page?
>
> But I began thinking, "There must be a way using
> xsl:if or xsl:when or xsl:choose or xsl:otherwise to
> make it so I could have ONE and one only XSL file for
> the whole site.

Not sure why this (a single XSLT file) is important to you ... is it a 
maintenance problem?  Throwing the logic for documents conforming to 
multiple DTDs into a single stylesheet has its own maintenance challenges.

On brief review your vocabularies look mutually exclusive ... a single XSL 
stylesheet can support documents from multiple DTDs just by having the 
respective templates all in one stylesheet.  When you have a vocabulary 
conflict you have to get into using modes, which starts with some of the 
challenges.

But if you write a push-oriented stylesheet then you can accommodate 
different document models with a single XSLT file.

But I'm not really sure why you want one stylesheet for everything.  If you 
do have common templates, stylesheet modularization can done with 
<xsl:include/>.

> The idea is that no matter whether I was generating an
> opening Subject screen or a page further in, all the
> info. I need should be in this XML file.

Why not modularize the common data, maintain it in a single location, and 
use the document() function to pull into your transform?  That will improve 
your maintenance of your data without having copies of information in each 
XML file.

> I have tried many ways, but it is clear that I still
> don?t truly understand which commands are appropriate
> and how to incorporate them into the XSL?

Separate <xsl:template> instructions sit there waiting to be fired by the 
<xsl:apply-templates/> that pushes nodes to the stylesheet.  Since you have 
element types from different DTDs, you can just let the ones that do not 
apply sit there and never fire, and the ones that do apply actually get used.

I hope this helps.

................... Ken

>   Reference Dept.
>   Stockton-San Joaquin County Public Library

p.s. we are delivering XSL training in the San Francisco area the week of 
March 22 ... check out our home page for venue, pricing and registration 
details ... perhaps we can help you and your colleagues.


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