W3C home > Mailing lists > Public > www-rdf-logic@w3.org > June 2003

Re: reference needed (URIs and what they refer to)

From: Dan Connolly <connolly@w3.org>
Date: 04 Jun 2003 23:19:35 -0500
To: Lynn Andrea Stein <las@olin.edu>
Cc: Sandro Hawke <sandro@w3.org>, www-rdf-logic <www-rdf-logic@w3.org>
Message-Id: <1054786775.21350.1150.camel@dirk.dm93.org>

On Wed, 2003-06-04 at 16:15, Lynn Andrea Stein wrote:
> > Resent-From: www-rdf-logic@w3.org
> > From: Sandro Hawke <sandro@w3.org>
> > Date: Wed Jun 4, 2003  3:12:53  PM US/Eastern
> > To: www-rdf-logic <www-rdf-logic@w3.org>
> > Subject: Re: reference needed
> >
> >> but what if we're using
> >> an inferencing engine to reason about RDF statements? Would the engine
> >> treat all occurrences of SlashURIs as referring to the thing itself,
> >
> > All URIs in RDF refer to things themselves.  Those things themselves
> > might be web pages.
> But the URI (e.g., http://www.w3.org/Consortium/) construed in RDF (or 
> RDFS or OWL)  can't simultaneously refer to
> 1) the bits returned by http get on that particular page
> 2) whatever happens to be the current description of the W3C
> let alone
> 3) the Consortium itself
> etc.

Try looking at it as referring to an agent/object/doodad
that responds to GET requests with content bits.

Perhaps this analogy helps:

In programs, identifiers refer to variables, which
have values. In the web, URIs refer to resources
which have representations.

This is illustrated by the 1st whiteboard diagram from
the TAG Irvine minutes:

(the diagrams after the 1st one were explorations
into levels of detail where there's much less

The 26 March web architecture draft tries to explain
it; the TAG is leaning toward starting with
a simpler scenario before introducing the
fragment identifier stuff. And we're likely to include
a figure. But perhaps it helps explain... or perhaps
the readers here can help the TAG tell the story...

> In particular, if the bits returned are different tomorrow, 
> interpretation (1) says either the URI still refers to the old bits OR 
> the reference relation has changed -- the URI maps onto a different 
> thing tomorrow

so don't look at it that way.

>  -- while (2) says that the reference relation has 
> remained the same while the referenced object has (internally) changed 
> (its representation).

yes, that's pretty much the idea... most HTTP URIs that
don't have #s in them work that way; certainly
http://www.w3.org/Consortium/ does.

> So, while I agree completely that
> >
> > I think the RDF Model Theory is very clear that URIs (aka URIRefs)
> > function in RDF just like constant symbols in classical logic.  No
> > dereferencing is involved in knowing that each URI acts (within an
> > interpretation) as a name for something in the domain of discourse.
> >
> I've never been quite clear on which the (some)thing(in the domain of 
> discourse) is that the URIRef names.  I suppose that I can use it 
> however I want, but only at the risk of diluting the U -- universality 
> -- in the URI.  And of course all three of (1) the bits returned (2) 
> the (changing) current description and (3) the Consortium are things 
> and so properly nameable by URIs....the question is just *which* URI 
> (or *which* thing).

Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 5 June 2003 00:19:08 UTC

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