RE: [xsl] Answers to review questions in "Beginning XSLT": Chapter 7

["Lars Huttar" <lars_huttar@xxxxxxx>]

Hello Jeni,

Thanks for going through those answers and responding.

> > 4. Assuming that the prefix tv is associated with the namespace
> > http://www.example.com/TVGuide within the stylesheet, what kinds of
> > elements do the following expressions select?
> >
> > Answer:
> >
> > Program -- any child element of . named "Program" in no namespace
> > tv:* -- any child element node of . in the 
> http://www.example.com/TVGuide
> >   namespace
> > tv:Program -- any child element of . named "Program" in the
> >   http://www.example.com/TVGuide namespace.
> > *[name() = 'Program'] -- same as just Program
> 
> Not quite. When you use the name() function, what you get depends on
> the prefix that was used in the source document.  If, in the source
> document, the http://www.example.com/TVGuide namespace is the default
> namespace, as in:
>
>   <Program xmlns="http://www.example.com/TVGuide";>
>     ...
>   </Program>
> 
> then name() = 'Program' might return true for that element.

Oops, I missed that.  Thanks.
In other words, select="Program" is quite different from
select="*[name() = 'Program']", as the former says "no namespace"
and the latter says "the default namespace in the source doc."

> I say might because if the namespace is *also* declared with the
> prefix 'tv', as in:
> 
>   <Program xmlns="http://www.example.com/TVGuide";
>            xmlns:tv="http://www.example.com/TVGuide";>
>     ...
>   </Program>
> 
> then the processor is free to return either "Program" or "tv:Program".
> It doesn't matter what prefix was actually used on the element, only
> what prefixes are declared for the element's namespace.

This makes sense; but then don't you think the definition on p. 247 is a bit misleading?

  "name() returns the full name of the element or attribute as given
  in the source document, including the prefix if there is one."

Anyway, the revised answers:
 *[name() = 'Program'] -- a child element of . named Program that is in the
   default namespace (that is in scope at this point in the source document)
   (or no namespace if there is no default).
 *[starts-with(name(), 'tv:')] -- a child element of . that is in the namespace
   associated with the tv: prefix in the source document.
 *[name() = 'tv:Program'] -- a child element of . named Program that is
   in the namespace associated with the tv: prefix in the source document.


> Excellent. In general I'd avoid using count() if you can because naive
> processors are likely to collect all the nodes that the path selects
> so that they can be counted. If you use:
> 
>   preceding-sibling::*[name() = $name] or
>   following-sibling::*[name() = $name]
> 
> then a processor can stop looking once it's found the first preceding
> or following sibling with the same name (and doesn't even have to look
> at the following siblings if it finds a preceding sibling with the
> same name).

Good point.  Since we're not really interested in the total number,
it makes more sense to just test for existence of siblings.

Thanks again for your help.

Lars


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