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RE: Restricting attribute use from optional to required

From: Michael Kay <mike@saxonica.com>
Date: Wed, 26 Aug 2009 09:06:28 +0100
To: 'Jan Přidal' <jan.pridal@gmail.com>, <xmlschema-dev@w3.org>
Message-ID: <F5C72987EB244580AF2A22D99B7491EE@Sealion>

There's an assymetry here between attributes and child elements. For the
content model (child elements), when you restrict a type you have to restate
all the parts of the content model that you want to inherit. For attributes,
you only have to list the things that have changed - any other attributes
are inherited automatically.

(No, I can't justify why it was designed that way. Like most things in XSD,
it was probably because there were too many bright people on the committee
and each of them got their way on one feature of the language.) 

Regards,

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


> -----Original Message-----
> From: xmlschema-dev-request@w3.org 
> [mailto:xmlschema-dev-request@w3.org] On Behalf Of Jan Pridal
> Sent: 26 August 2009 08:23
> To: xmlschema-dev@w3.org
> Subject: Re: Restricting attribute use from optional to required
> 
> OK, so let's say we get rid off this repeating of content 
> model declaration using named model group, see below.
> There's still one place I'd like to fix - the enumeration of 
> all attributes from 'attributes' attributeGroup inside the 
> 'parentWithReqLabelAttr' type declaration.
> 
> <xsd:attributeGroup name="attributes">
>   <xsd:attribute name="label" type="xsd:string" />
>   ...
> </xsd:attributeGroup>
> 
> <xsd:group name="commonElements">
>   <xsd:sequence>
>       ...
>   </xsd:sequence>
> </xsd:group>
> 
> <xsd:complexType name="parent">
>   <xsd:group ref="commonElements"/>
>   <xsd:attributeGroup ref="attributes"/> </xsd:complexType>
> 
> <xsd:complexType name="parentWithReqLabelAttr">
>   <xsd:complexContent>
>     <xsd:restriction base="parent">
>       <xsd:group ref="commonElements"/>
>       <xsd:attribute name="label" type="xsd:string" use="required"/>
>       ... list all remaining attributes from 'attributes' group!!!
>     </xsd:restriction>
>   </xsd:complexContent>
> </xsd:complexType>
> 
> <xsd:complexType name="derivedWithOptLabelAttr">
>   <xsd:complexContent>
>     <xsd:extension base="parent">
>       <xsd:sequence>
>         <xsd:element ref="style"/>
>       </xsd:sequence>
>       <xsd:attribute name="icon" type="xsd:string" use="optional"/>
>     </xsd:extension>
>   </xsd:complexContent>
> </xsd:complexType>
> 
> <xsd:complexType name="derivedWithReqLabelAttr">
>   <xsd:complexContent>
>     <xsd:extension base="parentWithReqLabelAttr">
>       <xsd:sequence>
>         <xsd:element ref="parameter" minOccurs="0" 
> maxOccurs="unbounded"/>
>       </xsd:sequence>
>       <xsd:attribute name="name" type="xsd:string" use="required"/>
>     </xsd:extension>
>   </xsd:complexContent>
> </xsd:complexType>
> 
> I'd like to have there something like a restriction of 
> attributeGroup, either local or a global inside the type 
> 'parentWithReqLabelAttr':
> 
> <xsd:attributeGroup name="attributesWithReqLabelAttr">
>   <xsd:attributeGroup ref="attributes">
>     <xsd:attribute ref="label" use="required"/>
>   </xsd:attributeGroup>
> </xsd:attributeGroup>
> 
> If this can be achieved then I would be able to add a new 
> attribute to the 'attributes' attributeGroup without changing 
> the 'parentWithReqLabelAttr' type. However as far as I know 
> there's no such mechanism.
> 
> Jan Pridal
> 
> 2009/8/17 Michael Kay <mike@saxonica.com>:
> >> But it is then more than a little bit awkward - as I have to add a 
> >> new complexType that restricts the complexType 'parent'
> >> and then within it I have to repeat all the stuff declared the 
> >> 'parent' and its parent types (by extension) etc.
> >
> > Yes, that's a particularly nasty feature of derivation by 
> restriction.
> >
> > If you're only restricting the attributes, and not the 
> content model, 
> > you can get around it by having both the base type and the derived 
> > type reference the same named model group.
> >
> > Regards,
> >
> > Michael Kay
> > http://www.saxonica.com/
> > http://twitter.com/michaelhkay
> >
> >
> 
Received on Wednesday, 26 August 2009 08:07:07 GMT

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