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RE: Relax NG, Thoughts, etc.

• To: "'Burak Emir'" <Burak.Emir@e...>
• Subject: RE: Relax NG, Thoughts, etc.
• From: "Michael Kay" <michael.h.kay@n...>
• Date: Mon, 29 Nov 2004 10:15:48 -0000
• Cc: <xml-dev@l...>
• In-reply-to: <41AAE429.3010100@e...>
• Thread-index: AcTV8UaC+1mZTM4aTqWAw6kKpgmhmAACgbsg

> Granted, dynamic validation (=at runtime) is always possible, 
> but it is 
> certainly not a big help. Errors are discovered after having gone to 
> production, doesn't sound good to me.

Actually, it's an enormous help compared with not doing it at all.

I agree that static checking, where possible, is even better. Saxon doesn't
do any static checking against a schema yet. 

> I am sure you will not try to add exact static typing based 
> on Relax NG for XSLT in the next version of Saxon? 

No, but I wouldn't rule it out eventually.

> There are papers that analyze 
> this for subsets of XSLT

Can you give me a reference? I'm not aware of such papers.

> but doing it exactly, for the full 
> language, 
> is - as far as I remember - undecidable.

Even with XML Schema, it's unprovable that a given stylesheet is guaranteed
to create valid output (to do strict static typing, in the style of the
XQuery static typing option, we would have to throw out
xsl:apply-templates). But pragmatically, I think it's possible to give
static warnings for a good proportion of user errors. And I suspect that
most of the heuristics to do this are equally applicable to DTDs or Relax
NG.

Michael Kay

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