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Re: ISSUE-58: Scalability of URI Access to Resources

From: Chimezie Ogbuji <chimezie@gmail.com>
Date: Fri, 7 Sep 2007 12:04:46 -0400
Message-ID: <f6ec8dcb0709070904o72ed3a18taa7f0aea85b8f1ab@mail.gmail.com>
To: "Williams, Stuart (HP Labs, Bristol)" <skw@hp.com>
Cc: www-tag@w3.org

On 9/7/07, Williams, Stuart (HP Labs, Bristol) <skw@hp.com> wrote:
> Hello Chimezie,
>
> So... I'm going to be a little obtuse, maybe deliberately so... but
> maybe I should also make it clear what is bugging me, which is the use
> of the prefix RDF in the term "RDF URI"... they are just URIs... I don't
> see what insisting on calling them "RDF URI" buy's you.

I see I have failed (perhaps miserably) in making this point.

> I'm afraid that didn't help me :-(. I certainly understood the semiotic
> triangle stuff and have been exposed to it before.
>
> As 'symbol' what makes "RDF URI" (your term)  different from URI in
> general.

See below.

> > This is mostly a rehash from http://www.w3.org/TR/rdf-mt/ (so
> > I hope Pat will slap me on the hand when I'm chatting
> > rubbish), but generally, RDF URIs are 'symbols' which denote
> > things in an interpretation (a 'theory').
>
> And URI in general do not? Even in the particular interpretation that we
> might commonly call 'the web'?

URI's in general denote 'resources' but (formal) denotation IMHO is
only as useful as the inference capabilities it facilitates.  If this
wasn't the case, there would be no reason to bring KR into the picture
(i.e., 'the web' + KR = 'semantic web')

> > The expressions in
> > which the RDF URIs are used describe a set of conditions that
> > must be met to satisfy the interpretation.  The end-game
> > (goal, if you wish) is "to provide a technical way to
> > determine when inference processes are valid, i.e.
> > when they preserve truth."
>
> I don't understand how I can tell whether or not I'm using an "RDF URI".

>From the context.  An unparsed RDF/XML document is nothing more than
an information set, with QNames composed from URIs.  The namespace
names denote 'resources' (per URI RFC), but this denotation is
basically inert: there is no mechanism to guide inference (or
interpretation).

After you parse the document into an instance of the RDF abstract
model, you have a different context and different mechanisms apply (by
normative specifications).  They are still URIs in the RFC 2396 sense,
but the denotation is no longer inert.

> OTOH, I can tell when I'm using a URI in RDF (or HTML or an email or...)
>
> > The main difference is that the domain of discourse is a
> > superset of what Web architecture is primarily concerned
> > with: information resources and their representations.
>
> Though I think Pat would wish it otherwise, I don't think that in terms
> of the denotation of URIs, the domain of discourse in Web Arch is
> constrained in the way that you describe.

Note, I said 'primarily'.  Consider that a majority of the 'Good
practice' assertions in AWWW are relevant only to representations.

> > Whereas in a model-theoretic language, the 'semantics' are
> > determined from the expressions which make use of the RDF
> > URIs, Web architecture is (or it seems that way from the
> > specific best practices in AWWW) primary concerned with the
> > consumption of information resources to meet a different
> > goal: a user browsing a page, or a web crawler browsing pages
> > to create indices for subsequent searching.
>
> Hmmm.... I'll think about that. There is a particular artiefact, AWWW, a
> document which is an expression of a set of principles and best
> practices that we could agree on (at the time). However, there is the
> much larger conceptual artifact of "The Architecture of the Web". Whilst
> AWWW speaks mostly of what it calls "information resources" the scope of
> what URIs can (and I'll use the word here risking a blast from Pat)
> identify (by which I mean 'refer-to') is unconstrained by AWWW.

Yes, they are certainly unconstrained, since it essentially describes
a 'resource' as something which is consistent with arbitrary
referents.  It is not so much the constraint (or lack thereof) that
bothers me but when attempts are made to make authoritative claims (or
suggest that such claims can be 'found' - hence the load on the
transport level and the original point of relevancy for ISSUE-58 )
about the nature of referents independent of a formal inference
mechanism.

> > By the context of its use.
> > http://metacognition.info/profile/webwho.xrdf#chime is the
> > URI I've 'minted' to represent me.
>
> ok...
>
> > When used as a link in an
> > HTML document, it is simply a (typed) link to my FOAF
> > document.
>
> Hmmm... less ok... assuming that you are serving as
> "application/rdf+xml" the by virtue of the RDF media type definition
> that is still a reference to you, the person, rather than a bit of text
> in an RDF/XML representation of a graph - or more accurately it is a
> reference to a/the thing in an intepretation which statisfies the
> assertions made in the graph (which in all probability is you).

Point well taken, my example was poorly-formed and the media-type
gives you enough information to essentially 'blur' the distinction.

> FWIW: I believe that "unique denotation of URI" is an intention the
> design of Web Architecture; I am equally aware that such a position
> denies "context of use" as a means to disambiguate the referrents of
> referring expressions. I am equally aware that in general the context in
> which a referring expression occurs can be significant. I have never
> been able to square that circle - though the closest I have come is to
> regard the web as one big context and referrents of references made
> using URI as invariant within that (large) context.

That is a very difficult circle to square, yes.  However, abstracting
the web as one big context works against interpretation - since
something more sophisticated (i.e., KR) is needed for this.  I would
suggest that if the context is significant *precisely* because it
gives a (mostly) unambiguous path to determining the nature of
referents  then its usage should not be denied.

> It seems like a
> design choice in the design of Web Architecture - it is I think the
> place where the constraints of the Web apply to the semantic web.

Hmm.. /me will need to sleep on that one =)

-- Chimezie
Received on Friday, 7 September 2007 16:04:53 UTC

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