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Derivation by restriction

From: <zongaro@ca.ibm.com>
Date: Thu, 2 Aug 2001 17:21:50 -0400
To: www-xml-schema-comments@w3.org
Message-ID: <OF139F17B2.4FE86DF9-ON85256A9C.0069E5E3@torolab.ibm.com>
Hello,

    The following schema document came from Kohsuke Kawaguchi.  My reading 
of 3.4.2 of the Schema recommendation [1], is that the type rrr is a restriction of the ur-type, and according to "Complex Type 
Definition with complex content" in the table in 3.4.2, the {content type} 
of rrr is empty.  That should mean that the restriction of rrr is not a valid restriction.

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema'>
  <xs:element name="dummy"/>
 
  <xs:complexType name="rrr" />
  <xs:complexType name="sss">
    <xs:complexContent>
      <xs:restriction base="rrr">
        <xs:sequence>
          <xs:element name="dummy"/>
        </xs:sequence>
      </xs:restriction>
    </xs:complexContent>
  </xs:complexType>
</xs:schema>

     I believe that it was intended that this document violate the "Schema 
Component Constraint: Derivation Valid (Restriction, Complex)" defined in 
3.4.6 of the Schema recommendation [2].  It appears that, of cases 5.1 to 
5.3 in that constraint, case 5.3 applies.  I've copied it below.  However, 
that case requires that the particle of the complex type definition be a 
valid restriction of the particle of the {content type} of the {base type 
definition}; but in this schema, the {base type definition} has no 
particle, so it doesn't appear truly to violate case 5.3.

5.3 If the {content type} of the {base type definition} is mixed or the {content type} of the complex type definition itself is element-only, then the particle of the complex type definition itself must be a ·valid restriction· of the particle of the {content type} of the {base type definition} as defined in Particle Valid (Restriction) (§3.9.6).

     Is there something else that makes it clear that the restriction is 
not a valid restriction?  Or does the use of the definite article in the 
phrase "the particle of the {content type} of the {base type definition}" 
imply that the {content type} must have a particle, and so must not be empty?

Thanks,

Henry

[1] http://www.w3.org/TR/xmlschema-1/#declare-type
[2] http://www.w3.org/TR/xmlschema-1/#derivation-ok-restriction
------------------------------------------------------------------------
Henry Zongaro      XML Parsers development
IBM SWS Toronto Lab   Tie Line 778-6044;  Phone (416) 448-6044
mailto:zongaro@ca.ibm.com
Received on Thursday, 2 August 2001 17:21:54 GMT

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