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Re: Confused about Primer Example section 4.7 vs Structures Constraint on Complex Types Sec 5.11 Extension particularly 1.1.4.1

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 09 Nov 2000 10:25:41 +0000
To: "Bob Schloss/Watson/IBM" <rschloss@us.ibm.com>
Cc: www-xml-schema-comments@w3.org
Message-ID: <f5bzoj9bfx6.fsf@cogsci.ed.ac.uk>
"Bob Schloss/Watson/IBM" <rschloss@us.ibm.com> writes:

> My reading of Structures "Constraints on Complex Types",
> Section 5.11 http://www.w3.org/TR/2000/CR-xmlschema-1-20001024/#coss-ct
> Derivation Valid (Extension)
> clause 1.1.4 and particularly clause 1.1.4.1 makes me think that
> the Primer Example in "Abstract Elements and Types" section  4.7
> http://www.w3.org/TR/2000/CR-xmlschema-0-20001024/#abstract
> has a definition for complexType "car" which is not allowed.
> 
> Is this a problem of me being unable to see the parsing of all the
> "ands" and "ors" which are in clause 1.1.4 of
> Derivation Valid (Extension) paragraphs of Section 5.11 of Structures?
> 
> Primer example:
> 
> <complexType name="Vehicle" abstract="true"/>
> 
> <complexType name="Car">
>          <complexContent>
>                  <extension base="target:Vehicle"/>
>           </complexContent>
> </complexType>
> 
> 
> Structures: clause 1.1.4 of  Derivation Valid (Extension) paragraphs in
> section 5.11:
> 
>    Either the {content type} of the {base type definition} and the {content
> type} of the complex
>    type definition itself must be the same simple type definition, or else
> the {content type} of
>    the complex type definition itself must specify a particle and either
> the {content type} of the
>    {base type definition} must be empty or
>        1.1.4.1  both {content type}s must be mixed or both must be
> element-only;

I _think_ this is all OK.  Bear in mind this is a constraint on schema 
components, not XML representations.  So saying 'must specify a
particle' is really the same as saying 'must have complex content' (as 
opposed to simple content).  The example above satisfies all this,
because per the correspondence rules for extension [1], 

   "2.1 if the explicit content is empty, then the {content type} of
        the type definition resolved to by the normalized value of the base
        [attribute]"

you'll end up with a vacuous extension, which has a content
type==particle, which will itself be a valid extension, because no
change at all is a valid extension.

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 Thursday, 9 November 2000 05:25:46 GMT

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