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Re: choice group particel whose {particles} is empty

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 26 Sep 2002 09:24:15 +0100
To: "Stanley Guan" <stanley.guan@oracle.com>
Cc: <xmlschema-dev@w3.org>, "Schema Interest Group" <w3c-xml-schema-ig@w3.org>
Message-ID: <f5bvg4t17m8.fsf@erasmus.inf.ed.ac.uk>

"Stanley Guan" <stanley.guan@oracle.com> writes:

> There is a difference between choice and {all, sequence} group particles 
> in determining whether its {content type} is empty or whether a particle
> is pointless:
>    choice -- {particles} is empty plus its {min occurs} is 0
>    {all, sequence} -- {particles} is empty
> 
> It looks to me that the following two groups are different:
>    choice A -- its {minOccurs} = 0 and {particles} is empty
>    choice B -- its {minOccurs} = 1 and {particles} is empty
> 
> For choice A, its {content type} is empty and it's 
> pointless.  For choice B its {content type} is not
> empty and it's not pointless because it defines a "negative
> group particle" where no sequence (including empty sequence) of
> element information items can be valid with respect to it.
> 
> Is this interpretation correct?

In all respects but, possibly, one.  Groups don't have a {content
type} property, so I'm not sure what you mean by reference to it.

If you mean that a complex type definition which _has_ such a choice
as its content model is emptiable, then yes,
 A ---> emptiable, B -x-> emptiable

ht
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2002, 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/
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Received on Thursday, 26 September 2002 04:24:17 GMT

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