Re: XPath/XSLT 2.0 concerns
Jeni Tennison wrote: > Sure, but there's a lot of stuff being put into XPath 2.0 precisely so > that XSLT processors *can* do this schema-dependent optimisation. I'm > trying to get at whether that stuff is worthwhile or not. Well, the obvious schema-dependent optimisations are - take shortcuts while traversing the input tree for doing selects and building key tables - take advantage of known cardinalities of selected node sets - avoid exception handling in expressions, for example like handling NaNs in "1+$whatever", and perhaps taking shortcuts in evaluating expressions The last point can also almost be done without schema information, the only major difference being that the input values for the expression have to be checked before the expression is evaluated rather than during input validation. Whether any of the other two optimisations above will pay off depends very much on the schema. If you have a large input document and a very non-uniforn schema (unlike the usual DB query results or XHTML), it may be worthwile, in particular if you are sloppy and/or heavily utilise the descendant, previous and following axes. However, I can see a schema aware XSLT as a development aid, the same sense as a type system for other progarmming languages. Wouldn't it be nice to get warnings that select="record/filed" is always empty (because of the typo) and that 1+customername might be non-numeric? I belive it could catch a lot of small problems in early development stage which otherwise could even evade quite serious testing. > and even then, it's utility hasn't yet been proven empirically. Well, nobody really tried yet, so who knows? I belive the ability to catch certain problems at style sheet compile time, or at least at the first run, can easily save thousands of man-hours of work. I just had an example where writing select="output" instead of select="outputs/output" had cost me two full days :-\. J.Pietschmann
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