Re: anyAttribute via attributeGroup refs problem

ht@inf.ed.ac.uk wrote on 11/11/2008 08:36:12 AM:

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> Michael Kay writes:
>
> >> Yes, I would have expected a union in the same way single
> >> attribute definitions form a union, since my personal view up
> >> to now on "anyAttribute" was that it's just a slightly more
> >> generalized "attribute". Obviously, it's not, but treated
> >> quite differently. Haven't thought on this long enough, but:
> >> are there use cases for namespace intersections?
>
> Yes, when you have negated wildcards (##other), intersection is
> typically what you want.  Consider a v1 schema designed for
> extensibility, which includes a attribute for 'standard'
> attributes, and an allowance for extensibility:
>
>  <xs:attributeGroup name="standard">
>   <xs:attribute ref="xml:base"/>
>   <xs:attribute ref="xml:id"/>
>   <xs:attribute ref="v1:owner"/>
>   . . .
>   <xs:anyAttribute namespace="##other" processContents="lax"/>
>  </xs:attributeGroup>
>
> Now, in the v2 schema, I want to define a group which adds an
> attribute to that group and still allows extension:
>
>  <xs:attributeGroup name="standard">
>   <xs:attributeGroup ref="v1:standard"/>
>   <xs:attribute ref="v2:status"/>
>   <xs:anyAttribute namespace="##other" processContents="lax"/>
>  </xs:attributeGroup>

Assuming v1 and v2 are bound to different namespaces I don't believe this
is legal [1] (see clause 2 of Attribute Group Definition Representation OK)
in XML Schema 1.0. I'm pretty sure in Xerces we emit an error because the
intersection [2] of the two negations is not expressible.

> Intersection is what you want here -- extension attributes are allowed
> provided they are qualified with _neither_ v1 _nor_ v2.  Union would
> be useless, as that would allow _any_ qualification, including v1 or
> v2.
>
> I agree the situation is less than ideal, one would really like much
> more detailed control over what happens.
>
> ht
> - --
>        Henry S. Thompson, School of Informatics, University of Edinburgh
>                          Half-time member of W3C Team
>       10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131
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>                 Fax: (44) 131 651-1426, e-mail: ht@inf.ed.ac.uk
>                        URL: http://www.ltg.ed.ac.uk/~ht/
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spam]

Thanks.

[1] http://www.w3.org/TR/xmlschema-1/#src-attribute_group
[2] http://www.w3.org/TR/xmlschema-1/#cos-aw-intersect

Michael Glavassevich
XML Parser Development
IBM Toronto Lab
E-mail: mrglavas@ca.ibm.com
E-mail: mrglavas@apache.org