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Re: A new proposal (was: Re: which layer for URI processing?)

From: John Cowan <jcowan@reutershealth.com>
Date: Fri, 26 May 2000 12:21:06 -0400
Message-ID: <392EA472.8E013078@reutershealth.com>
To: Jonathan Borden <jborden@mediaone.net>
CC: Tim Berners-Lee <timbl@w3.org>, xml-uri@w3.org
Jonathan Borden wrote:

>         This is a tricky problem. What is the definition of
> "R1 equivalent R2"?

I think you mean "How do we decide whether R1 is equivalent to R2"?  The
answer comes from outside the system: two URIs identify the same resource
if the provider of the resource says that they do.  "Saying so" may be
informal, or may be formalized as RDF, thus:

	<RDF:Description about="(some URI)>
		<xx:same href="(some other URI)">
		<xx:different href="(a third URI)">
	</RDF:Description>
	
>         We have already ascertained that a simple byte comparison of R1 and R2
> won't suffice because the two may have an abstract equivalency. It seems
> that the equivalency is a priori based on the equality of u1 and u2.

Au contraire.  If URIs are string-equal, they identify the same resource.
If URIs are not string-equal, a scheme-specific procedure may exist that
tells us they identify the same resource anyway.  Beyond that, we fall back
on extracurricular knowledge.  In no case is accessing the resource either
necessary or sufficient, as I proved in an earlier message.

>         For example "el cid":
> 
>         "cid:contents" = "cid:contents"  (these are absolute URIs no :-?)

That is not a valid "cid:" URL per RFC 2392, which invokes RFC 2405, which
says that content-IDs must have the syntax of Message-IDs and must be
world-unique.

A valid cid: URL would be "cid:scritchifchisted@skunk.reutershealth.com".

>         If so, then why not just 'define' the resources returned as a result of
> binding two relative uris as equivalent? Suppose I define a new scheme
> "rel:". Is
> 
>         "rel:light" == "rel:light" by definition?
> 
> (answer the question and I'll tell you how the rel: protocol works :-))

The answer depends on the definition of the specific "rel:" scheme, a
question out of scope for 2396.
 
-- 

Schlingt dreifach einen Kreis um dies! || John Cowan <jcowan@reutershealth.com>
Schliesst euer Aug vor heiliger Schau,  || http://www.reutershealth.com
Denn er genoss vom Honig-Tau,           || http://www.ccil.org/~cowan
Und trank die Milch vom Paradies.            -- Coleridge (tr. Politzer)
Received on Friday, 26 May 2000 12:22:38 UTC

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