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deriving simple content from mixed

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 04 Oct 2001 19:09:26 +0100
To: www-xml-schema-comments@w3.org
Message-ID: <f5bzo77l1k9.fsf@cogsci.ed.ac.uk>
There's a contradiction between chema Representation Constraint:
Complex Type Definition Representation OK [1] and clause 5.1.2 of
Schema Component Constraint: Derivation Valid (Restriction, Complex)
[2]:

  5.1 If the {content type} of the complex type definition is a simple
  type definition, then one of the following must be true:

    5.1.1 The {content type} of the {base type definition} must be a
    simple type definition of which the {content type} is a valid
    restriction as defined in Derivation Valid (Restriction, Simple)
    (3.14.6).

    5.1.2 The {base type definition} must be mixed and have a particle
    which is emptiable as defined in Particle Emptiable (3.9.6).

In the face of this contradiction, implementations are free to go
either way.  In due course the WG will have to resolve the
contradiction.  I will argue that 5.1.2 should stay, and a clause
added to the mapping and XML representation sections to accommodate
this.  It seems inconsistent to

 a) allow mixed content elements to have defaults;
 b) allow mixed content types to be restricted to empty;
 c) *not* allow mixed content types to be restricted to text-only with 

    a type.

[1] http://www.w3.org/TR/xmlschema-1/#src-ct
[2] http://www.w3.org/TR/xmlschema-1/#coss-ct
-- 
  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 Thursday, 4 October 2001 14:08:45 GMT

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