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> >Nothing in a schema can make an XPath 1.0 expression invalid. What is
> >possible is that by examination of a schema you can
> statically determine
> >that a particular XPath expression will return an empty node-set.
>
> That seems to me a very dangerous thing to do. While you could
> determine that this is true for *valid* documents, not all documents
> are valid, not even all documents that reference a schema. XPath
> (both 1.0 and 2.0) does not require validity. A conformant XPath
> processor should not fail when faced with an invalid but well-formed
> document.
>
> I suppose it would be possible to first test validity, and then, once
> the document had been validated, use these optimizations. However,
> I'm not sure that this would actually buy you anything in the long
> run.
It will probably be possible in XSLT 2.0 to state that a stylesheet is
designed to work only with source documents that are valid against a
particular schema. This will enable the stylesheet to be optimized to
process such documents, and to reject documents that are not valid against
that schema. Obviously this will be optional; it will still be possible to
write generic stylesheets to process any well-formed document.
Michael Kay
Software AG
home: Michael.H.Kay@ntlworld.com
work: Michael.Kay@softwareag.com
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