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Re: Equivalence classes

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 19 Feb 2000 10:03:02 +0000
To: www-xml-schema-comments@w3.org
Message-ID: <f5bya8hik6h.fsf@cogsci.ed.ac.uk>
Philip Wadler <wadler@research.bell-labs.com> writes:

> Henry writes:
> 
> > As currently spec'ed you can only nominate a global element as the
> > exemplar of an equivalence class, so you example is invalid to start
> > with.
> 
> Thanks, that answers my first question (as I suspected, in the negative).
> But not my second, repeated here.
> 
> > If it's not possible, what was the rationale for omitting it?
> 
> By the way, I consider this on the critical path to getting a report
> out the door, in the sense that the report needs to explain rationales
> for this and other decisions.  Cheers, -- P

W3C specs do _not_ contain rationales for their design decisions:
that would make them monsters beyond reading.

The rationale in this case is that there is no guarantee of uniqueness 
of reference: there can be multiple local element declarations with the same 
name within different complex types, and thus no way with a 'ref'
attribute of type QName to distinguish between them.  XPath could do
it, but the additional complexity was not judged worth the marginal
increase in functionality.

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/
Received on Saturday, 19 February 2000 05:03:05 GMT

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