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Re: choice group particel whose {particles} is empty

From: Stanley Guan <stanley.guan@oracle.com>
Date: Thu, 26 Sep 2002 09:59:23 -0700
Message-ID: <018301c2657e$10e39470$c5b42382@us.oracle.com>
To: "Henry S. Thompson" <ht@cogsci.ed.ac.uk>
Cc: <xmlschema-dev@w3.org>


----- Original Message -----
From: "Henry S. Thompson" <ht@cogsci.ed.ac.uk>
To: "Stanley Guan" <stanley.guan@oracle.com>
Cc: <xmlschema-dev@w3.org>; "Schema Interest Group"
<w3c-xml-schema-ig@w3.org>
Sent: Thursday, September 26, 2002 1:24 AM
Subject: Re: choice group particel whose {particles} is empty


> "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.
>

For the "group" here, I mean a group particle like all, choice or
sequence as the terminology used in 3.9.6.

My main question is how useful choice B is?  Is it main use
is like what I said -- "negative particle"?

> 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

Yes, this is what I mean.

>
> 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/
>  [mail really from me _always_ has this .sig -- mail without it is forged
spam]
>
Received on Thursday, 26 September 2002 13:06:03 GMT

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