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Closure for XML Schemas

From: Murali Mani <mani@CS.UCLA.EDU>
Date: Thu, 7 Dec 2000 22:20:03 -0800 (PST)
To: www-xml-schema-comments@w3.org
Message-ID: <Pine.SOL.4.10.10012072146220.4003-100000@panther.cs.ucla.edu>

My previous question to the schema WG was about CFGs appearing in the
content model. You had replied that it was handled in a way similar to
what RELAX does -- by not allowing recursion in model groups.

I had another question now -- will there be a definition of closure
properties under boolean set operations, such as union, intersection and
difference for XML Schema? I believe, XML Schema will not be closed under
union and difference. It should not be surprising that most query
operations also will not be closed under XML Schema. I believe one of the
usage scenarios of XML Schema is for query?

And databases do not work without closure. Also, I do not think we can
obtain closure by restrictions on XML Schema. XML Schema is not closed
because it is much restricted and less expressive than, say RELAX.

Is this something which XML Schema will consider?, in such a case, I find
it better that for some purposes, we use a closed schema language. I
believe RELAX will be closed under all boolean set operations as well as
query operations (from the properties of regular tree languages). 
Therefore will it be possible for the Schema WG to combine forces with
RELAX, and define something when we require such closure properties. From
where I stand, it appears that RELAX is not being given any consideration,
which I believe it deserves.

I would appreciate the views of the Schema WG on this.

thanks and regards - murali.
Received on Friday, 8 December 2000 01:20:37 UTC

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