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RE: Understanding Restrictions on Groups

From: Michael Kay <mike@saxonica.com>
Date: Tue, 26 Jun 2007 13:16:02 +0100
To: "'Henry S. Thompson'" <ht@inf.ed.ac.uk>, "'Eliot Kimber'" <ekimber@innodata-isogen.com>
Cc: <xmlschema-dev@w3.org>
Message-ID: <007901c7b7eb$c37068b0$7d037283@turtle>

> The motivation is to provide an invariant rather like that of 
> object-oriented programming languages:  any valid member of a 
> type defined by restriction is also a valid member of the 
> type defined by its base.

I think that what this demonstrates is that's there's a set of use cases
where what people want is "a schema that's the same as X except for
difference D", with no constraints on the nature of the difference D - it
might be making a mandatory element optional, or adding values to an
enumeration, or changing something from float to double.

People imagine that's what xs:redefine was designed for, and perhaps it
should have been. Rather like overriding in XSLT, come to think of it - no
constraints requiring compatibility with whatever it is you are overriding.

Michael Kay
http://www.saxonica.com/
Received on Tuesday, 26 June 2007 12:16:33 GMT

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