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   Re: XLink a special case in the self-describing Web?

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  • From: ht@cogsci.ed.ac.uk (Henry S. Thompson)
  • To: "Steven R. Newcomb" <srn@techno.com>
  • Date: 22 May 2000 10:18:31 +0100

"Steven R. Newcomb" <srn@techno.com> writes:

> Please correct me if I'm wrong about any of this.
> (1) XML Namespaces do not provide a way for a single element to
>     conform to an element type in each of several schemas.  Therefore,
>     there is no way for a single element to be recognized as
>     conforming to both the X:Foo and the Y:Bar element types.
> (2) XLink is now just attributes; the element type can be anything.
>     This permits a single element to be recognized as an XLink and as
>     whatever else it may be.  (Whatever else it may be, it may still
>     only be one element type in one single namespace, as far as I
>     know.)  This is a kind of sleight-of-hand: XLink elements are
>     still XLink elements; we still expect certain combinations of
>     attributes to appear in certain contexts and not in others.
> So, if my above understandings are correct, I tentatively conclude
> from this that XLink is not a namespace or a schema in the usual
> sense, because, among all of the kinds of element definitions that are
> possible, only the XLink element types are, de facto, exempt from the
> "one element, one element type name in one semantic space of element
> type names" rule.
> Can anybody create sets of attributes, just as has been done with
> XLink, that will constitute a semantic space, and thus effectively
> have elements identify themselves as conforming to certain element
> types without requiring that the generic identifier be used to
> identify the element type?  

As I understand your question, the answer is straightforwardly 'yes': 
define a complex type with the relevant attributes, which any number
of element declarations can then exploit, either directly, or
indirectly by type definition derivation:

<schema targetNamespace="...xlink" ...>

 <attribute name="href">...</attribute>

 <compleType name="simpleLinkType">
  <attribute ref="xlink:href"/>

<schema targetNamespace="...newcomb">
 <import namespace="...xlink"/>
 <element name="foo">
   <complexType base="xlink:simpleLinkType" derivedBy="extension">
     [content model1]
     [your attributes2]

 <element name="bar">
   <complexType base="xlink:simpleLinkType" derivedBy="extension">
     [content model2]
     [your attributes2]

  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
		     URL: http://www.ltg.ed.ac.uk/~ht/

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