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RE: subtyping

From: Biron,Paul V <Paul.V.Biron@kp.org>
Date: Thu, 15 Feb 2001 17:44:27 -0800
Message-Id: <376E771642C1D2118DC300805FEAAF43014BAA82@pars-exch-1.ca.kp.org>
To: "'mccaleb@eeel.nist.gov'" <mccaleb@eeel.nist.gov>, www-xml-schema-comments@w3.org
> -----Original Message-----
> From:	mccaleb@eeel.nist.gov [SMTP:mccaleb@eeel.nist.gov]
> Sent:	Friday, December 15, 2000 2:04 PM
> To:	www-xml-schema-comments@w3.org
> Subject:	subtyping
> 
> 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.
> 
Thank you for your question.  The ability to simultaneously restrict and
extend types is something that the WG has considered, both for simply and
complex types.  However, the WG has decided that for version 1.0 of the
schema language, that support for this feature will not be supported.
However, we have recorded this as a possibility for future versions of the
spec.

thank you,

pvb
Received on Thursday, 15 February 2001 20:46:26 GMT

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