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

Re: semantics status of RDF(S)

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 3 Apr 2001 09:42:09 -0700
Message-Id: <v04210116b6eefbc81947@[]>
To: Sandro Hawke <sandro@w3.org>
Cc: www-rdf-logic@w3.org
>Peter F. Patel-Schneider wrote:
> > There has recently been a discussion on the semantic problems with RDF.
> >
> > I strongly agree with Pat Hayes's characterization of RDF (and RDFS) as
> > based on a fundamentally flawed semantic model
>I agree there's a flaw here.  I'm afraid it may be hard to really
>address it while maintaining the desired quality of RDF as "universal"
>and relatively independent of contentious design issues.

I honestly don't think so. The basic ideas of logical inference have 
been around now for about 2000 years and they still hold good even on 
the Web.

>I'm going to go out on a limb here and propose a solution that I think
>provides solid semantics without being unduly restrictive.  It's
>simple: reduce the RDF model to binary relations stated with
>locally-scoped terms which may be defined directly in English (not
>indirectly as URIs attached to semantics by various standards bodies
>and by application developers).

Not sure I follow this, but English is not a good way to state 
semantic meanings!

>More formally, in prolog syntax, the RDF model would be defined as
>having two relations:
>   binary_relation(subject_term, relation_term, value_term).
>which means that the relationship identified by the relation_term (by
>the mechanism defined below) is truly held between some object
>identified by the subject_term and some object identified by the
>value_term, respectively.
>The definitional grounding for the relation_term and optionally for
>the other terms would be provided by:
>   english_definition(term, "This is English text which defines something").
>This approach allows semantics to be defined with arbitrary precision
>for humans by allowing the inclusion of entire textbooks or legals
>codes if necessary.

But it doesnt provide any model-theoretic semantics, since English 
doesnt have a model theory. The point is not to pin down the meaning 
for English readers, but to provide a mathematically checkable notion 
of valid inference for machines.

>And it allows machine processing via the
>crude-but-effective mechanism of exact matching of strings.

The longer the prose gets, the harder it is to get exact string matching.

> In
>effect, English text strings become the unique-identifiers which
>people are using in RDF today.

I will agree that allowing a broader notion of unique-identifier 
might be handy.

Pat Hayes

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Received on Tuesday, 3 April 2001 13:55:00 UTC

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