Re: Allowable schema representations

[Loz]

Eddie Robertsson wrote:

W3C XML Schema language permits different content models for elements 
with the same name, as long as the validator can unambiguously 
determine which content model applies. Your examples are legal.

Not really. See comment below.
If I define an XML schema as follows:
<?xml version="1.0" encoding="UTF-8"?>
<!-- strange.xsd -->
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema";
                        targetNamespace="http://localhost/strange";
                        xmlns="http://localhost/strange";
elementFormDefault="qualified">
<xsd:complexType name="C1">
<xsd:sequence>
      <xsd:element name="A" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="C2">
      <xsd:sequence>
      <xsd:element name="A" type="C1"/>
<xsd:element name="A" type="xsd:string"/>
This is not legal in W3C XML Schema. In order to have two elements with 
the same name in the same content model they also _must_ have the same 
type. This constraint is violated in the above type.
The spec reads [1]:

*"Schema Component Constraint: Element Declarations Consistent*
If the {particles} <http://www.w3.org/TR/xmlschema-1/#particles> 
contains, either directly, indirectly (that is, within the {particles} 
<http://www.w3.org/TR/xmlschema-1/#particles> of a contained model 
group, recursively) or �implicitly� 
<http://www.w3.org/TR/xmlschema-1/#key-impl-cont> two or more element 
declaration particles with the same {name} 
<http://www.w3.org/TR/xmlschema-1/#e-name> and {target namespace} 
<http://www.w3.org/TR/xmlschema-1/#e-target_namespace>, then all their 
type definitions must be the same top-level definition, that is, *all* 
of the following must be true:
1 all their {type definition} 
<http://www.w3.org/TR/xmlschema-1/#type_definition>s must have a 
non-�absent� <http://www.w3.org/TR/xmlschema-1/#key-null> name.
2 all their {type definition} 
<http://www.w3.org/TR/xmlschema-1/#type_definition>s must have the same 
name.
3 all their {type definition} 
<http://www.w3.org/TR/xmlschema-1/#type_definition>s must have the same 
target namespace."

Cheers,
/Eddie
Thanks for pointing that out. I've included a second example at the end 
of this message. My reading of the constraint you pointed out makes me 
believe it is ok. IBM's SQLC tool (thanks Bob) validates it OK. Would 
you agree with that reading?

Also should a raise a bug against xerces, or has someone already taken 
care of that?

thanks, again, for your help.
Loz
<?xml version="1.0" encoding="UTF-8"?>
<!-- strange.xsd -->
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema";
            targetNamespace="http://localhost/strange";
            xmlns="http://localhost/strange";
            elementFormDefault="qualified">
        <xsd:complexType name="C1">
                <xsd:sequence>
                        <xsd:element name="A" type="xsd:string"/>
                </xsd:sequence>
        </xsd:complexType>
        <xsd:element name="A" type="C1"/>
</xsd:schema>

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