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Re: Restricting substitution groups?

From: Eric van der Vlist <vdv@dyomedea.com>
Date: Fri, 07 Dec 2001 18:02:09 +0100
Message-ID: <3C10F611.60907@dyomedea.com>
To: xmlschema-dev@w3.org
Sorry to insist ;=) ... is the question that stupid or a FAQ?

Eric

Eric van der Vlist wrote:

> Given that a substitution group is kind of equivalent to xs:choice:
> 
> http://www.w3.org/TR/xmlschema-1/#cos-particle-restrict
> 
> 
> 2.1 Any top-level element declaration particle (in R or B) which is the 
> {substitution group affiliation} of one or more other element 
> declarations is treated as if it were a choice group whose {min occurs} 
> and {max occurs} are those of the particle, and whose {particles} 
> consists of one particle with {min occurs} and {max occurs} of 1 for the 
> top-level element declaration and for each of the declarations in its 
> ·substitution group·.
> 
> Does that mean that we can restrict substitution groups?
> 
> If for instance I have:
> 
> <xs:element name="head"/>
> <xs:element name="a" substitutionGroup="head"/>
> <xs:element name="b" substitutionGroup="head"/>
> <xs:element name="c" substitutionGroup="head"/>
> 
> and:
> 
> <xs:complexType name="base">
>   <xs:sequence>
>     <xs:element ref="head"/>
>   </xs:sequence>
> </xs:complexType>
> 
> is
> 
> <xs:complexType name="derived">
>   <xs:complexContent>
>    <xs:restriction base="base">
>     <xs:sequence>
>       <xs:choice>
>         <xs:element ref="a"/>
>         <xs:element ref="b"/>
>       </xs:choice>
>     </xs:sequence>
>    </xs:restriction>
>   </xs:complexContent>
> </xs:complexType>
> 
> a valid restriction?
> 
> I guess not since it doesn't seem to match the condition for restricting 
> choices:
> 
> Schema Component Constraint: Particle Derivation OK (Choice:Choice -- 
> RecurseLax)
> For a choice group particle to be a ·valid restriction· of another 
> choice group particle all of the following must be true:
> 1 R's occurrence range is a valid restriction of B's occurrence range as 
> defined by Occurrence Range OK (§3.9.6);
> 2 There is a complete ·order-preserving· functional mapping from the 
> particles in the {particles} of R to the particles in the {particles} of 
> B such that each particle in the {particles} of R is a ·valid 
> restriction· of the particle in the {particles} of B it maps to as 
> defined by Particle Valid (Restriction) (§3.9.6).
> NOTE: Although the ·validation· semantics of a choice group does not 
> depend on the order of its particles, derived choice groups are required 
> to match the order of their base in order to simplify checking that the 
> derivation is OK.
> 
> The question should then probably be which is the order of the elements 
> of a substitution group when they are mapped to a xs:choice during 
> validation (and how can this be used to restrict a substitution group) ?
> 
> Thanks
> 
> Eric
> 



-- 
See you in Orlando for XML 2001.
                                     http://www.xmlconference.net/xmlusa/
------------------------------------------------------------------------
Eric van der Vlist       http://xmlfr.org            http://dyomedea.com
http://xsltunit.org      http://4xt.org           http://examplotron.org
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Received on Friday, 7 December 2001 12:02:13 GMT

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