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Re: Must You Specify mixed="true" on extended types?

From: George Cristian Bina <george@oxygenxml.com>
Date: Fri, 09 Sep 2005 13:42:12 +0300
Message-ID: <43216704.9000207@oxygenxml.com>
To: Eliot Kimber <ekimber@innodata-isogen.com>
Cc: xml-schema-dev <xmlschema-dev@w3.org>

Hi Eliot,

I think that Xerces is right here.

The extended type has an empty effective content which means that its 
content type property is the same as the one of the base type, see the 
rules for computing the content type for complex types with complex content:
3.2 If the <extension> alternative is chosen, then  the appropriate case 
among the following:
3.2.1 If the ·effective content· is empty, then the {content type} of 
the type definition ·resolved· to by the ·actual value· of the base 

You can see that if you add a particle in the extended type
<xs:element name="an-element">
       <xs:extension base="SomeType">
	  <xs:element name="test"/>
         <xs:attribute name="newatt" type="xs:string"/>

Xerces will also corectly report that:

SystemID: E:\workspace\oXygen\test.xsd
Location: 13:34
Description: E cos-ct-extends. The content type of a 
derived type and that of its base must both be mixed or both be 
element-only. Type '#AnonType_an-element' is element only, but its base 
type is not.
URL: http://www.w3.org/TR/xmlschema-1/#cos-ct-extends

Best Regards,
George Cristian Bina
<oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger

Eliot Kimber wrote:
> I have declarations of the form:
> <xs:complexType name="SomeType">
>   <xs:complexContent mixed="true">
>     <xs:sequence>
>       <xs:element ref="ns:someElement"/>
>     </xs:sequence>
>   </xs:complexContent>
> </xs:complexType>
> <xs:element name="an-element">
>   <xs:complexType>
>     <xs:complexContent>
>       <xs:extension base="SomeType">
>         <xs:attribute name="newatt" type="xs:string"/>
>       </xs:extension>
>     </xs:complexContent>
>   </xs:complexType>
> </xs:element>
> Xerces 2.6 and 2.7 both pass this, as does oXygen (which I believe uses 
> Xerces for schema processing). An older version of Stylus Studio throws 
> an error, saying that the extended type (an-element) must specify 
> mixed="true" or the base type must specify mixed="false".
> A reading of "Schema Component Constraint: Derivation Valid (Extension)" 
> suggests that Stylus is in fact correct:
> " Both {content type}s must be mixed or both must be 
> element-only."
> But I wanted to make sure, because I would have expected the value for 
> "mixed" to be inherited from the base type for extensions, regardless of 
> what the nominal default value of the "mixed=" attribute is.
> That is, it feels like "Simon Says" behavior to have to specify 
> mixed="true" for extensions when the base complex type specifies 
> mixed="true". Obviously, specifying mixed="false" when the base type 
> specifies mixed="true" would be an error. But if the extending type 
> specifies nothing for mixed, it should reflect the value specified for 
> the base type.
> Also, if this is required by the spec, then Xerces appears to not be 
> validating it all, because in my tests it didn't catch the case where 
> two declarations explicitly disagree on the value for mixed=.
> Thanks,
> Eliot
Received on Friday, 9 September 2005 10:36:56 UTC

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