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Re: requesting XML records

From: Mike Taylor <mike@indexdata.com>
Date: Thu, 27 Mar 2003 17:37:14 GMT
Message-Id: <200303271737.h2RHbEj17516@badger.miketaylor.org.uk>
To: matthew.dovey@las.ox.ac.uk
CC: a.powell@ukoln.ac.uk, www-zig@w3.org

> Date: Thu, 27 Mar 2003 17:06:47 -0000
> From: "Matthew Dovey" <matthew.dovey@las.ox.ac.uk>
> 
> > The issue here seems to be, what do we mean by one schema 
> > being "derived from" another?  Is there a ready-made answer 
> > to this from the world of XML Schema?  Or do we have to 
> > invent such a notion?
> 
> Not a direct mapping - in XML Schema we have redefines, import and
> substitution groups.

Isn't this a pretty typical XML Schema response?  "You can't do
exactly what you want, but here are three different ways to do things
that are kind of similar." :-)

> Roughly speaking these work as:
> 
> Redefines - in this case I say that I take schema A, but for a
> particular element x I say what structure I what it to be rather
> than the structure given in schema A.
> 
> Import - If I import schema A into schema B, then at any point in
> the structure I'm defining for schema B, I can introduce a structure
> references in schema A
> 
> Substitution groups - I import Schema A, but say that for a
> particular element x in schema A, I can in fact substitute an
> element y in defined in schema B

Thanks for this neat little tutorial.  Then do you think it would make
sense to say any of the following three alternative things?

	When a client requests that records be returned in a
	schema A, the server may also return records in
	schemas formed by redefining elements of A.

	When a client requests that records be returned in a
	schema A, the server may also return records in
	schemas that import A.

	When a client requests that records be returned in a
	schema A, the server may also return records in
	schemas formed by substituting elements of A.

-- or maybe  --

	When a client requests that records be returned in a
	schema A, the server may also return records in
	schemas formed by redefining and substituting elements
	of A.

And equally important: would any of these restricted degrees of
freedom give Theo the flexibility he needs?  Could you get from DC to
a loose-DC Schema by redefinitions and substitutions only?

 _/|_	 _______________________________________________________________
/o ) \/  Mike Taylor  <mike@indexdata.com>  http://www.miketaylor.org.uk
)_v__/\  "You used to know but now you've forgotten" -- Lightning
	 Seeds, "Marvellous"

--
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Received on Thursday, 27 March 2003 12:37:41 GMT

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