W3C home > Mailing lists > Public > www-rdf-interest@w3.org > August 2002

'shared meaning' landgrab?

From: Dan Brickley <danbri@w3.org>
Date: Fri, 23 Aug 2002 17:26:34 -0400 (EDT)
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
cc: <seth@robustai.net>, <sean@mysterylights.com>, <www-rdf-interest@w3.org>
Message-ID: <Pine.LNX.4.30.0208231643030.22101-100000@tux.w3.org>

Hi Peter,

On Fri, 23 Aug 2002, Peter F. Patel-Schneider wrote:

> From: "Seth Russell" <seth@robustai.net>
> Subject: Re: A Rough Guide to Notation3
> Date: Fri, 23 Aug 2002 10:03:15 -0700
> > From: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
> [...]
> > > This is a matter of some contention.  In fact, I would argue that one of
> > > the main problems with the Semantic Web vision is precisely this view that
> > > the Semantic Web is tied to simple labeled directed graphs.

I share your concern that people may be expecting far too much of our
(intentionally) simplistic triple-based data format. But I'm happy having SW
"tied to" triples in the sense that much (most?) application instance data can be
couched in those terms without excessive contortion. I'm far less
enthusiastic about FOL-carried-thru-triples, but I expect the exchange of
FOL to be a niche interest on the Web for a while yet. Hmm... At this
point commentators often invite a comparison of the uptake of RDBMS vs  more
general KR / logic programming techniques in the industry at large...
I'm not sure that we should be intimidated by this history, but it does
perhaps establish that something as simple-minded as RDF 1.0 graphs could
prove a useful stepping stone.

> > Why?  Strangely enough  I happen to believe it is the current obsession with
> > applying formal logic to language that is one of the main problems with the
> > Semantic Web.  Imho, the Semantic Web is about communication and finding
> > whatever we are looking for.  I have yet to see a single application of
> > formal logic that has furthered that goal.

> Well, how are you going to ascribe a common meaning to the graphs you are
> sending around?

This was the main point I wanted to engage with, and the reason for the
change in Subject: line... I believe comments such as yours re 'common
meaning' to be over-enthusiastic marketing for a technical approach which
strangely enough *avoids* engaging with many of the challenges of 'common
meaning'. The proposed Model Theoretic formalisations of RDF, OWL etc only
scratch the surface of this problem. It is imho simply incorrect to
suggest that the RDF/OWL formalisations fix a 'common meaning' for such
content. They are a powerful tool, but not only address limited aspects of
the problem.

A Model Theory for (Semantic)Web content shows us how to stick to
truth-preserving operations on Web documents/messages with propositional
content, ie. those XML documents that are candidates for being true or
false (in some interpretation). But the MT approach is, by design, silent
on the imho more interesting part of the puzzle. Namely, the problem of
fixing the shared propositional content of these RDF/XML documents, such
that scattered parties throughout the Web can use them to communicate. The
MT specs alone can't fix the content of the RDF/XML, ie. determine the
claims they make about the world.

From http://www.w3.org/TR/rdf-mt/ "Since the exact nature of the things in
the universe is irrelevant, it is convenient to use the nodes of the graph
themselves as their own denotations."

MTs are happy with such trickery, since they only care that there are
satisfying interpetations, and not whether the symbol->world mapping
corresponds to the "common meaning" that people have in mind when encoding
claims in RDF/XML.

So it strikes me that you're making something of an unwarranted land-grab
on the term 'shared meaning'. I agree that MTs may help us detect and
repair miscommunications, but it seems too strong to claim that
formalisations in the MT tradition are enough to fix a common 'shared
meaning' for RDF/XML documents. Other ingredients come into play here,
notably the URI specifications. Unlike MTs, the URI spec does address this
aspect of the shared meaning problem, since it is concerned with
establishing machinery by which can write down names for things in an
agreed syntax and with common (if tangled, poorly articulated) rules about
the mapping between symbol and world.

> > > >    It *is* all about the graph !
> > >
> > > Why should the Semantic Web be restricted to such a limited mechanism?
> >
> > Well I do not view it as a limited mechanism.  I have a long standing
> > challenge, seeAlso (knowledge representation),  that says that I can
> > represent anything that can be expressed in any language with labeled
> > directed graphs.  To this day nobody has met that challenge to my
> > satisfaction.
> Well, how do you *represent* - and here I mean represent, not encode - the
> following first-order sentence using *only* labeled directed graphs?

I'm just about happy with 'encode'. FOL-in-RDF is like FOL-in-JPEG as far
as naive RDF (and JPEG) tools are concerned.  They just don't see the big
picture of the claims being carried through the RDF.

This 'encode' vs 'represent' is the crux of  the problem, it seems... do
you have a preferred definition of these concepts?


Received on Friday, 23 August 2002 17:26:38 UTC

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