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Re: subtyping

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 09 Jan 2001 13:46:52 +0000
To: mccaleb@eeel.nist.gov (Michael McCaleb)
Cc: www-xml-schema-comments@w3.org
Message-ID: <f5bk884rg6r.fsf@cogsci.ed.ac.uk>
mccaleb@eeel.nist.gov (Michael McCaleb) writes:

> Dear XML Schema editor,
> 
> Observation:
> In doing a comparison between the EXPRESS data modeling language (ISO
> 10303-11) and XML Schema, I noticed that in EXPRESS it is possible to
> create a subtype that both is a restriction (e.g., attribute value range
> restriction) of its supertype and an extension (e.g., an addition of
> another attribute) of its supertype. From the expressions for simpleContent
> complexContent (see below) it appears that in order to do the same thing in
> XML Schema that in intermediate throw away subtype would need to be
> created.
> 
> <simpleContent
>   id = ID
>   {any attributes with non-schema namespace . . .}>
>   Content: (annotation? , (restriction | extension))
> </simpleContent>
> 
> 
> <complexContent
>   id = ID
>   mixed = boolean
>   {any attributes with non-schema namespace . . .}>
>   Content: (annotation? , (restriction | extension))
> </complexContent>
> 
> 
> Question:
> Would it be worthwhile to permit both restriction and extension to be in
> the same simpleContent and complexContent.

We've considered this on several occasions, and concluded that the
mapping is already sufficiently complex that making it _more_ complex
to achieve something you can already do in two steps is not a win.

Thanks, and sorry to be so long getting back to you.

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 Tuesday, 9 January 2001 08:46:56 GMT

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