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From: "Murali Mani" <mani@CS.UCLA.EDU>
> On Thu, 12 Jun 2003, Michael Kay wrote:
>
> > > Thanks for the clarification, these are the things I was
> > > hoping someone could tell me, using for iterator etc, have we
> > > introduced more non-closed operators?? Has someone looked at
> > > them closely..?? I suspect there will be some more operators
> > > of this nature in XPath 2.0..
> >
> > The input and output of XPath operations are constrained to be values
> > described by the XPath data model. In that sense the language is closed.
> > Whether the data model has the particular mathematical properties you
> > are looking for is something I can't easily judge.
>
> That is right, with respect to values they are closed. But the question is
> with respect to schema.. I think this might be useful to know these
> mathematical properties..??
>
> Anyways, if someone does study all the operations of XPath, XQuery etc,
> and see under what they are closed (w.r.to schema), I think it might be
> useful..
Seems to me closure questions should be grounded in regular hedge (not
regular tree) grammars, as the output sequences of XPath/XQuery are, in
fact, hedges. I believe MURATA Makato has explored this territory (trees +
queries = hedges).
Bob
>
> cheers and regards - murali.
>
> > There are a few glitches in terms of closure, for example I'm not very
> > comfortable with the fact that the semantics of FLWR expressions in
> > XQuery are defined using a notion of "tuples" which are objects that
> > can't be represented directly in the data model, but overall I think
> > it's pretty clean.
> >
> > Michael Kay
>
>
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