W3C home > Mailing lists > Public > www-rdf-logic@w3.org > May 2001

Re: What do the ontologists want (what URIs denote)

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 15 May 2001 19:05:22 -0500
Message-Id: <v04210118b7276deb833f@[205.160.76.173]>
To: Dan Connolly <connolly@w3.org>
Cc: Jonathan Borden <jborden@mediaone.net>, www-rdf-logic@w3.org
>pat hayes wrote:
> >
> > >pat hayes wrote:
> > >[...]
> > >
> > > > The relationship between a URL and the
> > > > file it locates is not the same as that between a logical name and
> > > > what it denotes
> > >
> > >Er... huh? To me, the whole premise of rdf-logic is that
> > >the relationship between a URI (URL, if you like) *is*
> > >the same as that between a logical name and what it denotes.
> >
> > I know that is widely accepted as a premis. I also think it is
> > wrong,[later: see next para]  which is one reason why rdf-logic is in
> > such a tangle. It is symptomatic of the general carelessness about
> > use versus mention. The point of a URL in large part is that it
> > provides an electronic route map to the thing it locates. What you
> > get to is something that is readable and from which you might be able
> > to make inferences, right?
>
>Wrong.
>
>What a URI denotes is an abstract resource; you cannot,
>in the general case, directly observe it (i.e. you
>can't "read" it); you can only indirectly observe it
>by, for example, sending HTTP GET messages to it,
>and having it reply with a representation of its state.

Picky, picky. Someone might say that you never REALLY read a paper 
page, either, you just react to the photons that bounce off its 
surface. But thats just a switching-levels kind of argument.

Actually I think I disagree with this characterization. I (my 
computer) send GETs to a computer, and it sends me back a 
representation of its state, but that representation IS the web 
page/file/whatever is at that URL (at the moment I go looking, of 
course). Or at any rate, it is a copy of it.

>If it's a URI of the form NETADDR#NAME ,

Yes, but I was careful to say URL, not URI. Of course if we allow a 
pointer to a file that contains a name, then we will eventually get 
to names. That # sign has a meaning, right? It attaches a URL to a 
logical name. Of course *that* is a logical name, sure. But is the 
relationship between that and its denotation anything like that 
between http://www.coginst.uwf.edu/~phayes and a rather scruffy 
webpage? For example, you can't even send GET messages to most things 
that might be referred to by names.

>you can't
>even send messages to it; you can only send messages
>to NETADDR; then you might learn about what
>NETADDR#NAME denotes by interpreting some statements
>that mention NETADDR#NAME (or more likely, its
>short-form #NAME) in the response message.
>(an agent may, of course, consult any other source
>to find clues about the meaning
>of NETADDR#NAME.)
>
>Just take as an axiom that the relationship between
>a URI and a resource *is* the same as the relationship
>between a logical name and what it denotes. Try it
>on for size for a while.

Well, I have tried that. But what I can't get to fit is doing that at 
the same time as believing that URLs are URIs. If URLs are logical 
names, how in hell is my computer so good at finding their unique 
denotations, when it is so hopeless at finding any others? If I type 
"Neptune" it doesnt fetch me a planet.

Actually, more seriously: it may be that I do not know quite what a 
"resource" is. This term seems central to W3C lore but doesnt seem to 
be defined anywhere. Is there any kind of write-up on what it means? 
In particular, what kind of thing would NOT be a resource?

> > OK, so. Point taken. But then you have to fess up to the fact that
> > the relationship between any kind of machine-processable inferencing
> > and this standard interpretation has to be grounded in some
> > non-logical machinery.
>
>Yes, I've already fessed up to that...

OK, I hadnt read this before. But what I meant was that the reasoners 
that we are all going to build one day will need to be built in some 
non-reasoner way, in the sense that there isnt going to be any 
logical way that they can tell that the intended interpetation is 
being used.

>
>[[[
>The World Wide Web is a universal information space.
>Informally, we discuss the Web as if it were frozen in
>time and identical from all perspectives; we say that
>"the title of http://www.w3.org/xyz is 'One Fine Day'"
>despite the fact that the content---including the
>title---of this resource may change over time, and
>despite the fact that it may be available in French with
>a different title.
>
>To specify the protocols that govern the Web, it is
>essential to realize that in fact, the Web is a sort of
>mass hallucination shared among all the people and
>machines distributed around the globe who accept
>the principles of Web Architecture, much the way
>businesses and consumers accept the principles of an
>economy based on paper currency.

The trouble with this metaphor is that its the *machines* that have 
to be having the mass hallucination in the case of URLs. I could 
write a random URL-generator and go away, and my poor dumb laptop 
would go on getting hits all by itself; but if all the people went 
away, there really wouldnt be any money at all.

>By and large, we
>agree that there is one http://www.w3.org/xyz, even
>though each of us has slightly different experiences
>of it, much like by and large, people in the U.S. have a
>shared concept of the value of a dollar, even though
>in fact each person has a slightly different perspective
>on what they're willing to trade for one. The large
>scale effect is the result of each participant following
>the same principles when they communicate and
>interact with each other.
>
>When I say "the title of http://history.org/1492 is
>'Christopher Columbus goes to America'," all I really
>know is that my machine sent some packets to
>history.org and get back some packets with HTTP and
>HTML syntax that indicate a title of 'Christopher
>Columbus goes to America' (and I only believe that
>because I assume the machines didn't malfunction
>and weren't tampered with). If you follow that
>reference with your machine, you probably expect to
>see the same title even though I don't guarantee it for
>a fact.
>
>But your expectations are not the sort of "2+2=4"
>certainty. Nothing prohibits the history.org
>webmasters from setting up his server to return
>completely random results in response to requests for
>/1492.

Yes, but thats a different point. Truth and certainty arent the same 
thing. Nothing prevents anyone from printing nonsense in a book 
either: so what? That doesnt stop it being true that the book 
contains what it does, or stops other books from containing things 
that are true.

Pat Hayes

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Received on Tuesday, 15 May 2001 20:05:25 UTC

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