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RE: What are complexContent restrictions made for ?

From: zze-MARCHEGAY Michael stagiaire FTRD/DTL/LAN <michael.marchegay@rd.francetelecom.com>
Date: Wed, 22 May 2002 14:13:20 +0200
Message-ID: <0489A7888F080B4BA73B53F7E145F29A1B0ABE@LANMHS20.rd.francetelecom.fr>
To: "'Jeni Tennison'" <jeni@jenitennison.com>
Cc: "'xmlschema-dev@w3.org'" <xmlschema-dev@w3.org>
Hi Jeni,

> 
> 
> Hi MichaŽl,
> 
> > I'm trying to understand the interest of complexContent
> > restrictions, but I don't find in which kind of examples it is
> > usefull.
> [snip]
> > I can't figure out what is the difference between an element which
> > has type simpleName1 and another which has type simpleName2.
> >
> > So are complexContents just syntaxic sugar, used by XML Schema
> > processing tools or do they have another function?
> 
> You're absolutely right that in your example, the simpleName1 and
> simpleName2 complex types have exactly the same content model, so
> elements of those types are allowed exactly the same content.
> 
> However, the fact that simpleName1 is derived from personName can be
> significant. For example, if you were to declare an element with the
> type personName:
> 
>   <xsl:element name="name" type="personName" />
> 
> then an instance of that element could be assigned the type
> simpleName1 through the xsi:type attribute:
> 
>   <name xsi:type="simpleName1">...</name>
> 
> whereas it couldn't be assigned the type simpleName2.
> 

So a complexContent is usefull only when used in a type declaration,
isn't it ?

If I use one in a "inline" type definition for an element:

<xs:element>
  <xs:complexType>
    <xs:complexContent>
      <xs:restriction base="personName">
        <xs:sequence>
          <xs:element name="surname"/> 
        </xs:sequence>
      </xs:restriction>
    </xs:complexContent>
  </xs:complexType>
</xs:element>

this has **exactly** the same signification as if I write 

<xs:element>
  <xs:complexType>
   <xs:sequence>
     <xs:element name="surname"/> 
   </xs:sequence>
  </xs:complexType>
</xs:element>

isn't it ?

Thanks.

> Similarly, an element called simpleName could belong to the name
> element's substitution group if it had the type simpleName1 (because
> that's derived from the name element's type) but not if it had the
> type simpleName2.
> 
> So within the schema itself, and in terms of what you can do in the
> instance document, the fact that one of the types is derived from
> personName and the other isn't can make a significant difference.
> 
> The other way in which the type hierarchy can help is within
> processing tools that are aware of the PSVI. XSLT 2.0, for example, is
> on its way to becoming such a tool, which would mean that you'd be
> able to match all elements of type personName or simpleName1 with:
> 
> <xsl:template match="*[. instance of personName]">
>   ...
> </xsl:template>
> 
> whereas simpleName2 is unrelated to personName.
> 
> Thus, deriving by restriction is helpful because it enables you to
> express the commonality between a set of elements, and process them in
> the same kind of way.
> 
> Cheers,
> 
> Jeni
> 
> ---
> Jeni Tennison
> http://www.jenitennison.com/

--
MichaŽl Marchegay, Stagiaire France Telecom R&D du 11/02/2002 au 26/07/2002
Sous la responsabilitť d'Olivier Dubuisson
DTL/TAL - 22307 Lannion Cedex - France
> 
Received on Wednesday, 22 May 2002 09:17:11 UTC

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