W3C home > Mailing lists > Public > www-rdf-interest@w3.org > August 2000

Re: [Fwd: xmlns, uri+name pairs or just uris..? Clarification n eeded.]

From: Pierre-Antoine CHAMPIN <champin@bat710.univ-lyon1.fr>
Date: Tue, 01 Aug 2000 17:52:14 +0200
Message-ID: <3986F22E.8AED6596@bat710.univ-lyon1.fr>
To: "McBride, Brian" <bwm@hplb.hpl.hp.com>
CC: RDF-list <www-rdf-interest@w3.org>
"McBride, Brian" wrote:
> Perhaps I have misunderstood the relationship between the URI of a
> property and its namespace.  What is your understanding of what m&s
> says on this?
> 
> > As practical as it is (to give a clue to the parser about who
> > describing what),
> > this should not be a fundamental requirement,
> > or then RDF uses *locators* instead of *identifiers*, and
> > that's a shame because URLs are less general than URIs.
> 
> I didn't follow that bit.  How does the relationship between
> namespaces and URI's restrict RDF to using locators?

Let's be clearer (excuse me if I was confusing...)

As I understood XML Namespaces (XML-NS) the last time I read it,
a namespace is identified by a URI ; the URI does not have to be related to the namespace definition.
(anyway, no language is given in XML-NS for namespaces definitions. Note that DTDs can not do, as namespaces can define global attributes, which are out of DTDs'scope)

RDF M&S uses the namespace mechanism in the syntax it recomends, with 2 specificities:

 (a) qname are expanded to URIs by concatenating the namespace URI with the element name. This is not compliant with XML-NS, since the reverse transformation is not unique.

 (b) namespaces of RDF elements *must* be the URI of the schema defining those elements. This is a restriction of XML-NS.

I guess that (a) was motivated by the fact that URIs are more general than XML-NS pairs (namespace;tagname); the problem of the reverse transformation was implicitely solved by (reasonable) asumption that any vocabulary item has the form <schema>#<name> or <schema>/<name>, hence (b).

What I wanted to say is:
although reasonable, that asumption is too strong. URIs (identifers) differ from URLs (locators) in that: they do not *always* allow to retrieve the correpsonding resource. If they don't, the application should work anyway. If they do, very well, it will work better !

By restricting the property URIs to contain the URI of their defining schemas, RDF restricts itself to "friendly" URIs, which is IMHO a loss of generality.
Hope this is clearer.

> If an application can
> clearly distinguish between the original model and the annotions
> then, aside from implementation convenience, there should be no
> problem.

I believe that the property rdf:isDefinedBy is, by definition, a meta-property.
So there should be no problem with Dan's proposition of generating additional statements with that property.

  Pierre-Antoine
Received on Tuesday, 1 August 2000 11:52:48 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:51:43 GMT