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Re: Mixed content models and derivation

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 16 Oct 2001 12:54:21 +0100
To: Eric van der Vlist <vdv@dyomedea.com>
Cc: xmlschema-dev@w3.org
Message-ID: <f5b1yk3x0k2.fsf@cogsci.ed.ac.uk>
I haven't had time to work through all your questions, but here's the
basis on which things _should_ work:

1) The constraints on deriving content models from other content models
   are independent of whether or not the enclosing type definition is
   mixed or not.

2) The invariants must be respected: when deriving by restriction, the
   derived type must accept a subset of what the base type accepts; when
   deriving by extension the derived type must accept have as a prefix 
   something the base type accepts.

I _think_ it follows from this that

  a) when deriving by restriction you can stay the same, or go from
     mixed to unmixed, if all element content is optional, but never vice

  b) when deriving by extension you can stay the same, but never go
     from one to the other.

  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, 16 October 2001 07:53:37 UTC

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