At 11:08 AM 8/4/2008, Andrew wrote:
> I submit that speculating on performance differences vs alternatives is
> somewhat pointless, since it will depend on the implementation. It's not
> that it couldn't be optimized (especially if it were supported in the
> parser), so much as that it might not be.

In that case Wendell, there's no need to discourage anyone from using //

Indeed there isn't. :-)



Which is not to say that the battle-scarred veteran can't say "oh you 
know, that's likely to be expensive, and we've learned to work around 
potential problems with it in advance", etc.



I think we should be moderate in everything, which includes allowing 
for a certain amount of excess.



Just to recap:



- in 1.0 you don't have tunnelled parameters so you either pass the
information explicitly through each template which is prone to error
(and bad for your sanity), or you get it from the ancestor axis, which
could be expensive (and also isn't what you'd call elegant)

-- or you write a SAX filter that annotates the input tree and makes 
it really really fast ... elegance being in the eye of the beholder ...



- there is xml:lang and the lang() function, which were invented for
this particular task, but many implementations (including Saxon) will
just walk the ancestor axis behind the scenes, so you don't benefit
from switching to xml:lang from a proprietary solution

-- as far as performance goes, while allowing that there may or may 
not be other costs and benefits related to using a standard mechanism 
in your particular situation ...



This really isn't about premature optimisation...

Fair enough.



Cheers,
Wendell





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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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