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Re: qualification of components of an all group

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 21 Dec 1999 15:57:42 +0000
To: James Clark <jjc@jclark.com>
Cc: www-xml-schema-comments@w3.org
Message-ID: <f5bso0wnv61.fsf@cogsci.ed.ac.uk>
James Clark wrote:

> >  the components of a group whose <nt
> >  def="nt-compositor">compositor</nt> is (implicitly) <pt>all</pt>
> >  may not be qualified, > > and therefore call for exactly one
> >  appearance of the element they identify.

> What's the justification for this restriction?  * and & don't interact
> right in SGML, but I don't see why this can't be fixed in XML Schemas.

There was considerable concern expressed in the WG about the
implementation cost of unconstrained re-introduction of & into XML
Schema, with the result that we tied it down VERY hard.  I think we
probably over-reacted to that concern:  we can't even use it for the
content model for <datatype> because it doesn't allow ?.  That much at 
least I will lobby to have allowed, but I'm less sure about *:  do you 
want e.g.

 a b a

to be allowed by (a* & b),

or only e.g.

 b a a

i.e. would internal kleene operators be tightly bound?

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
     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 Tuesday, 21 December 1999 10:57:46 UTC

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