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XML Namespaces vs. RDF

From: Perry A. Caro <caro@Adobe.COM>
Date: Tue, 20 Jul 1999 14:40:54 -0700
Message-ID: <3794ECE6.FF48CB78@corp.adobe.com>
To: rdf-dev@mailbase.ac.uk, www-rdf-comments@w3.org
CC: xml-names-editor@w3.org
Hi!

Apologies if this is a dead horse that's been beaten round the bush a few
hundred times.

I'm unclear on how to implement lookup and comparison of property names in
RDF, in the context of XML namespaces.  The XML namespace spec
<http://www.w3.org/TR/REC-xml-names/> and the RDF spec
<http://www.w3.org/TR/REC-rdf-syntax/> seem to be in good agreement, except
for the following passage from the Formal Grammar for RDF section of the RDF
Spec:

	p is the expansion of the namespace-qualified tag name
	(Generic Identifier) of E. This expansion is generated
	by concatanating the namespace name given in the
	namespace declaration with the LocalPart of the qualified
	name.

It's this business about concatanating that worries me.  The XML namespace
spec never mentions concatanation as a valid mechanism.  Indeed, the
non-normative appendices seem to imply that the expansion of qualified names
should be treated as ordered pairs.

Consider the following RDF examples:

<rdf:RDF
  xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:foo="http://www.adobe.com/schema/property_">
    <rdf:Description about="">
	<foo:bar>a value</foo:bar>
    </rdf:Description>
</rdf:RDF>

vs.

<rdf:RDF
  xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:foo="http://www.adobe.com/schema/">
    <rdf:Description about="">
	<foo:property_bar>a value</foo:property_bar>
    </rdf:Description>
</rdf:RDF>

According the XML Namespace spec Appendix A.3, these two XML fragments
generate non-equivalent Expanded Element Types:

<ExpEType type="bar" ns="http://www.adobe.com/schema/property_"/>
vs.
<ExpEType type="property_bar" ns="http://www.adobe.com/schema/"/>

However, the RDF spec seems to suggest that both of the above RDF fragments
will generate the same dataset of triples, namely:

	{http://www.adobe.com/schema/property_bar, "", "a value"}

...which suggests that the two expansions are equivalent.

Which is right?  Am I reading too much into Appendix A.3?  Is the
concatanation mechanism suggested by RDF (and WebDAV, for that matter), a
deviation from the XML namespace spec?

Perry
Received on Tuesday, 20 July 1999 17:42:14 GMT

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