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Re: How does RDF/OWL formalism relate to meanings?

From: Dan Brickley <danbri@w3.org>
Date: Sat, 10 Apr 2004 00:45:30 -0400
To: Pat Hayes <phayes@ihmc.us>
Cc: Dan Connolly <connolly@w3.org>, public-sw-meaning@w3c.org
Message-ID: <20040410044529.GA8718@homer.w3.org>

* Pat Hayes <phayes@ihmc.us> [2004-04-09 23:19-0500]
> >I think I get it now...
> >
> >On Fri, 2004-04-09 at 16:19, Pat Hayes wrote:
> >I just scanned
> >the document, and nowhere does it say "each URI denotes a unique
> >resource"... at least not using the word "unique". I'll have
> >to re-read your message to public-webarch-comments, where
> >you excerpt lots of text that bothers you.
> >
> >I'm only aware of 1 at this point:
> >We still have "A URI must be assigned to a resource in order for agents
> >to be able to refer to the resource" which overstates the case since
> >you can refer to things using owl:InverseFunctionalProperty expressions
> >but without giving them URIs.
> >
> Maybe this could be (perhaps later in the document) modified or 
> expanded to something like
> "SW formalisms such as OWL provide ways to refer to resources 
> indirectly by describing their properties. This extends the reach of 
> the Web, by making it possible to refer to resources which do not 
> have a URI assigned to them but are suitably related to resources 
> identified by URIs."

Yes, I like this direction. We should be careful also to allow the 
possibility that the reference-by-description can be done with 
Literal-valued properties, as well as URI-valued properties (and for
that matter, bNode-valued properties, if such scenarios can plausibly be
concocted). Literal-valued properties are very useful for this, I think.
<c:Company c:nasdaqCode="MSFT" c:name="Microsoft"/> and suchlike can be
useful packets of information, without using URIs for anything beyond
the terms in the ontology. 

So I would change ending of your last sentence towards something like:
"...are suitably related to resources that are themselves 
unambiguously identified through appropriate descriptions or URIs"
(too wordy to actually use, but in that vein ok?)

> maybe with a disclaimer about this being relatively new and not fully 
> explored technology yet, or some such. 

Yes, I believe (in light of the 3-4 year FOAF experiment) that such a
disclaimer is appropriate. When we started FOAF there was no class 
owl:InverseFunctionalProperty. Now we have it, but I am not 100%
convinced the semantics it has (due to the approach we took to
formalising RDF and OWL) capture entirely what we need for
reference-by-description. Specifically, OWL allows that the
property/value pair might match different individuals in different 
interpretations, and guarantees "at most one"-ness only with regard to 
a single interpretation. In FOAF, I say that properties such as
foaf:mbox and foaf:homepage are "Static inverse functional properties",
as a (not yet formalised) way of claiming that they cannot take
different values at different times. If you believe "a1 foaf:homepage
d2", you should not be prepared to believe a2 foaf:homepage d2" at a
later date. I don't believe these issues are fully explored yet, so am
wary of sending an "OWL solves this once and for all" message.

>					That would both qualify the 
> overstatement appropriately, and also acknowledge that 'descriptive' 
> reference does ultimately depend on some kind of external anchoring 
> and can't be done *just* by describing things.

> >
> >>   You can't have it both ways. If the Web is essentially a trade in
> >> descriptions, then unique URI reference is achievable only by some
> >> external technique of rigid designation, many URIs are not unique
> >> identifiers, and most 'resources' are not uniquely designated or
> >> identified. Which is fine and fits OWL/RDF.
> >
> >Yes, quite.
> >
> >>  Or, if URIs really are required to be unique designators, ie names,
> >> then there needs to be some principled way to baptize resources with
> >> URIs.  Which would  be fine also.  And it would be fine to have some
> >> URIs one way and others the other way, as long as we could tell which
> >> was which for most purposes (which I think is close to the actual
> >> situation, in fact).  But right now we seem to have a reality which is
> >> descriptive, or a mixture, and a rhetoric which is insistently
> >> nominal, and they don't fit together. Which is not fine.
> >
> >Hmm... I guess I think of the architecture as being ideally nominal,
> >but practically descriptive.

That is a nice way of putting it. BTW the recent RDF-in-XHTML progress
raises prospect of reference-by-description at the level of hypertext
markup in human readable documents. This would/will/could be fantastic
for data merging and aggregation applications. Instead of writing:
<p>I went to the <a href="http://w3cfood.example.com/">W3C canteen</a>
for a delicious meal</p>, you'd write some expression (I forget the
syntax) that makes it clear that the prose fragment has as its
primaryTopic a "Restaurant" that has a homepage of [...] and maybe a
phoneNumber of [...]. Same for movie reviews etc. With some UI support
(eg. in weblogging tools) we could get quite a lot more clarity of
meaning in hypertext prose.

Note that this still works regardless of any worrying about formal OWL 
and reference-by-description issues. Our discussions there correspond
only to the distinction between saying "a" and "the", which I hope could
be clarified through annotating the properties/classes involved, without
change to instance data aspects of the problem.

Received on Saturday, 10 April 2004 00:45:30 GMT

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