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Re: emptiable content in particle inheritance

From: G. Ken Holman <gkholman@CraneSoftwrights.com>
Date: Mon, 02 Feb 2009 09:13:14 -0800
Message-Id: <7.0.1.0.2.20090202090917.024fa9d8@wheresmymailserver.com>
To: xmlschema-dev@w3.org

At 2009-02-02 11:33 +0100, Tobias Koenig wrote:
>there are the two schemas
>
>1)
><xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
>   <xsd:element name="doc" type="foo"/>
>     <xsd:complexType name="foo">
>       <xsd:complexContent>
>         <xsd:restriction base="bar">
>           <xsd:choice>
>             <xsd:element name="e1" minOccurs="0" maxOccurs="0"/>
>             <xsd:element name="e2"/>
>           </xsd:choice>
>         </xsd:restriction>
>       </xsd:complexContent>
>     </xsd:complexType>
>     <xsd:complexType name="bar">
>       <xsd:choice>
>         <xsd:element name="e1"/>
>         <xsd:element name="e2"/>
>       </xsd:choice>
>    </xsd:complexType>
></xsd:schema>
>
>2)
><xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
>  <xs:complexType name="base">
>    <xs:sequence>
>     <xs:element name="e1" type="xs:string" />
>    </xs:sequence>
>  </xs:complexType>
>  <xs:complexType name="derived">
>         <xs:complexContent>
>         <xs:restriction base="base">
>             <xs:choice minOccurs="0">
>                 <xs:element name="e1" type="xs:string" />
>             </xs:choice>
>         </xs:restriction>
>         </xs:complexContent>
>  </xs:complexType>
></xs:schema>
>
>In both cases a complex type with emptiable particle derives by restriction
>from a complex type with non-emptiable particle. However the first schema
>is valid according to xml schema test suite (and saxon validator) but the
>second is not. So what is the real issue in the second schema? That a choice
>particle is inherited from an sequence particle?

No, as I see it in schema (1) there is always a path through "foo" 
that conforms to "bar" ... there is no way through "foo" that does 
not conform to "bar".  This is because the only way through "foo" is 
with <e2> and <e2> is one of the ways through "bar".

In schema (2), however, there is a path through "derived" that does 
not conform to "base", that being no elements where "base" does not 
allow no elements.  Hence the processor cannot allow "derived" to be 
a restriction of "base" because it allows something that is not 
allowed in "base".

I hope this helps.

. . . . . . . . . . . . . Ken

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Received on Monday, 2 February 2009 17:15:44 GMT

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