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RE: The use of XML syntax in XML Query

• To: xml-dev@l...
• Subject: RE: The use of XML syntax in XML Query
• From: "Champion, Mike" <Mike.Champion@S...>
• Date: Thu, 3 Jan 2002 19:31:48 -0500

> -----Original Message-----
> From: Dare Obasanjo [mailto:kpako@y...]
> Sent: Friday, January 04, 2002 9:27 AM
> To: Champion, Mike; www-xml-query-comments@w...; 
> xml-dev@l...
> Subject: Re:  The use of XML syntax in XML Query
> 
> 
> I'm still waiting for someone with a theoretical background 
> to debunk the statements in the paper "On Database Theory and XML"[0] that

> it is is an unsolvable problem to guarantee that one can create a query 
> that for any given XML input will generate output that conforms to a
specified 
> XML schema.

To the best of my extremely limited knowledge, the XQuery people are somehow
working with  the theories behind XDuce.  "XDuce ("transduce") is a typed
programming language that is specifically designed for processing XML data.
One can read an XML document as an XDuce value, extract information from it
or convert it to another format, and write out the result value as an XML
document. Since XDuce is statically typed, XDuce programs never yield
run-time type errors and the resulting XML documents always conform
specified types."
http://xduce.sourceforge.net/  See the papers listed at
http://xduce.sourceforge.net/papers.html 

Whether XDuce is powerful enough to model something as big as XHTML as a
"specified type" is another matter, and whether this stuff can run fast
enough to be useful on real computers with real is another matter ... Again,
I know zilch about this other than these URLs, so someone from XQuery should
definitely weigh in here.

Also, how much of this kind of thing can be done in SQL, both as specified
in the latest standard and as implemented in real DBMS? Is there some way
for a SELECT statement to be constrained by some type definition so that it
will return only tuples that match the specified type?  

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