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RE: Naming

From: McBride, Brian <bwm@hplb.hpl.hp.com>
Date: Mon, 8 May 2000 17:45:09 +0100
Message-ID: <5E13A1874524D411A876006008CD059F239220@0-mail-1.hpl.hp.com>
To: www-rdf-interest@w3.org
>On Mon, 8 May 2000, Godfrey Rust wrote:
>
>> At 09:35 AM 5/8/00 +0100, McBride, Brian wrote:
>> >What resource does the URI 
>http://www.w3.org/2000/01/rdf-schema# name?
>> >
>> >Is it the namespace, the RDF Model, the XML serialization 
>or some abstract
>> >composition of all of them?
>> 
>> Or the particular manifestation or format of one of them as 
>it appears at
>> this location?  
>
>
>Great questions. Here's a meta-question:
>
>Is this a question about the RDF schema namespace URI, about 
>XML namespace
>URIs generally, or about Web architecture and URI naming in the general
>case? Unfortunately I don't think theres a clear answer, but 
>I'm inclined
>towards the latter.

The question first arose in my mind when I was rereading the RDF schema
spec and was disturbed by what I took to be the the use of the same
URI to denote both the RDF Schema and the RDF schema namespace.
Whilst the issue might have wider web architecture ramifications, what
schema is proposing feels like a violation of the principle
that a URI names a specific resource.

I think we have (at least) three questions here:

	1) schema using the same URI to denote a model and a namespace
	2) web architecture questions around what do URI's name
	3) the inclusion of a fragment identifier in a namespace URI


>...
>
>So one lesson here is that the resource 
>http://www.w3.org/Icons/WWW/w3c_main
>is itself not the thing that is transferred across the wire in an HTTP
>session. It's the Web's name for _something_.

I'm with you on this.  The URI names a resource.  In this case
I'm thinking it names an abstract resource, the w3c icon, and when a browser
is interacting with a server serving this resource, since the server
cannot deliver an abstract resource, a negotiation takes place to 
agree a concrete resource that can be delivered.  It is I think possible
to say what resource the URI names.

> What you get when you ask
>the Web about that thing, that resource, might well vary according to
>the kind of message you send it, the time of day, or other 
>properties of
>that resource.

I think I'm with you on this too, if I understand you correctly.  It is
pretty meaningless to ask about the size of 
http://www.w3.org/Icons/WWW/w3c_main.  I'm not sure how you would measure
the size of an abstract resource.  But you could ask about the size of 
a concrete resource such as the gif or png file.

If you are saying that if I asked about the 'status' of this resource
then I might get different answers depending on whether the resource
is available, then thats exactly what I'd expect.

>
>So, back to the XML/RDF namespace URI thing.
>
>From one perspective (bare XML namespaces with no additional 
>conventions
>layered on top), "http://www.w3.org/2000/01/rdf-schema#" is simply a
>string that can be used to compose URI references such as 
>http://www.w3.org/2000/01/rdf-schema#Class
>

The namespace spec says that a namespace has a URI.  That URI names the
namespace.  From the introduction of the namespace spec:

	An XML namespace is a collection of names,
	identified by a URI reference ...

What is the URI of the RDF Schema namespace?

>Per the URI RFC, the URI reference
>http://www.w3.org/2000/01/rdf-schema#Class is composed
>of a URI proper, http://www.w3.org/2000/01/rdf-schema and a fragment or
>view identifier, "Class". The interpretation of the latter is 
>relative to
>the mime type of the former. As I've shown above, in the general case a
>resource may use the Web to explose multiple mime-typed 
>representations of
>a resource. Access control, personalization etc also affect the
>representations that are available in different contexts.
>

Ok, now I think we're in fragment identifier territory.  What resource
does http://www.w3.org/2000/01/rdf-schema name?  What is its mime type?


>...

>
>Do folks here think the issues around URIs and Resources, and around
>identification of fragment identified views of representations of those
>resources, deserve a general treatment, or should we try to 
>figure out a
>perspective for those cases where the resource is (in some 
>sense) an RDF
>model? 
>
>In other words, do we expect there to be anything special about the
>answers we give Brian and Godfrey for
>
>http://www.w3.org/Icons/WWW/w3c_main#foobar
>
>versus for
>
>http://www.w3.org/2000/01/rdf-schema#foobar
>
>
>My inclination is to say that the Web needs a fix for both 
>cases, and that
>attempting an RDF-specific clarification here would be 
>unhelpful. ...

Unless a general solution is imminent, its a shame that the
schema spec get mired in these difficulties.  Could this
have been avoided by explicitly naming the various resources
e.g.

	http://www.w3.org/2000/01/rdf-schema/ names the model
	http://www.w3.org/2000/01/rdf-schema/namespace name the namespace
	http://www.w3.org/2000/01/rdf-schema/serialization.xml names an xml
document


Please bear in mind that I'm relatively unfamiliar with this
territory.  I'm just trying to relate what schema has done
with other specs, like URI and namespace.

On my current understanding, I'm concerned that Schema hasn't
stuck to the rules of these specifications.


Brian
Received on Monday, 8 May 2000 12:45:17 GMT

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