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RE: emptiable content in particle inheritance

From: Michael Kay <mike@saxonica.com>
Date: Mon, 2 Feb 2009 19:18:26 -0000
To: "'Michael Kay'" <mike@saxonica.com>, "'Tobias Koenig'" <tobias.koenig@trolltech.com>, <xmlschema-dev@w3.org>
Message-ID: <BE3C63A17FDA494BAFA8959C9B902388@Sealion>

Just to reinforce this, 4 validators (Saxon-SA, Xerces, XSV, and Ms .NET)
agree that the instance document

<doc/>

is valid against the schema

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
	<xsd:element name="doc" type="foo"/>
	<xsd:complexType name="foo">
	  <xsd:sequence>
		<xsd:element name="e1" minOccurs="0" maxOccurs="0"/>
	  </xsd:sequence>	
	</xsd:complexType>
</xsd:schema>

but invalid against

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
	<xsd:element name="doc" type="foo"/>
	<xsd:complexType name="foo">
	  <xsd:choice>
		<xsd:element name="e1" minOccurs="0" maxOccurs="0"/>
		<xsd:element name="e2"/>
	  </xsd:choice>	
	</xsd:complexType>
</xsd:schema>

I'm having great difficulty seeing how it can be valid against a particle P
but invalid against a choice of which P is one of the options. But that
seems to be the weight of opinion...

Michael Kay
http://www.saxonica.com/ 

> -----Original Message-----
> From: xmlschema-dev-request@w3.org 
> [mailto:xmlschema-dev-request@w3.org] On Behalf Of Michael Kay
> Sent: 02 February 2009 18:01
> To: 'Tobias Koenig'; xmlschema-dev@w3.org
> Subject: RE: emptiable content in particle inheritance
> 
> 
> 
> I remember having some trouble with <xsd:element name="e1" 
> minOccurs="0"
> maxOccurs="0"/> appearing as a branch of a choice, but I 
> forget the details.
> I've found a comment in the code that refers to test mgH014, 
> which I see is your schema (1), but I'm now far from 
> convinced about it.
> 
> Saxon is treating the choice as not emptiable - the only 
> valid content is the single element <e2/> - and Xerces 
> appears to agree. But at present I can't see from the spec 
> why that should be. The spec appears to say that the content 
> is valid against a choice model group if it is valid against 
> any branch of the choice, and the empty sequence certainly 
> appears to be valid against <xsd:element name="e1" 
> minOccurs="0" maxOccurs="0"/>. So I'm confused. I think I 
> might have been over-influenced by this published test result 
> and by the fact that other processors accept it as valid.
> 
> Michael Kay
> http://www.saxonica.com/
> 
> > 
> > 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?
> > 
> > Thanks in advance
> > 
> > Ciao,
> > Tobias
> > 
> 
> 
Received on Monday, 2 February 2009 19:19:10 GMT

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