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

RE: semantics status of RDF(S)

From: Danny Ayers <danny@panlanka.net>
Date: Mon, 2 Apr 2001 22:43:42 +0600
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: <www-rdf-logic@w3.org>
Are you in essence saying that for two parties to be able to communicate
successfully that their statements must ultimately refer back to a common
set of axiomatic definitions? and that RDF(S) should contain these but
I can see in the two examples you give how this might be feasible - in the
first case by providing a formal definition of negation within the schema or
at a URI, and including 'our version equivalentTo that one' somewhere in the
system. The second case seems a matter of dodgy wording ;-) But how much of
an ultimate reference can RDF(S) represent? Surely there will always be
things that are not formalised within RDF(S), so do you a) continually
extend it to encompass these things as they arise, or b) use 3rd party
extensions as required. Ok, so what's in RDF(S) now might need tightening
up, but surely that will get done before too long, in advance of which
what's wrong with using other formalisms, if necessary your own proprietry

<- Sure, anything can be represented in triples.  However, suppose that you
<- and I both want to represent negation in triples.  You use
<- reified statements
<- and the resource http://foo.bar.net/negation#not.  I decide to use an
<- s-expression encoding (i.e., represent statements as lists) and
<- http://research.buu.com/sexpr#negation.  We both provide a
<- decent semantics
<- for the triples we care about.  We both now have represented negation (or
<- quantification, or whatever).
<- However, our meaning does not come from the triples, and certainly is not
<- related to the meaning that RDF gives to triples.  It instead comes from
<- the semantics that we have provided and the encoding of this
<- meaning in the
<- triples.  Further, there is no way that we can directly use the
<- triples to
<- pass meaningful information back and forth between us.   The presence
<- of RDF and RDF(S) does not provide any help either.  The only way out of
<- this impass is if we understand the other formalism's encoding
<- and can undo
<- that encoding.
<- The situation can be even worse if we both actually meaningfully used RDF
<- and RDF(S) as part of our schemes due to the lack of a firm semantics for
<- RDF and RDF(S).  For example, suppose that I decided to use distributive
<- referents and alternatives to represent disjunction.  I might feel so
<- justified because of the statement ``An application using a
<- property whose
<- value is an Alternative collection is aware that it can choose any one of
<- the items in the list as appropriate.''  However, suppose that
<- you decided
<- that distributive referents didn't work this way on Alternative
<- collections
<- because of the statement ``Using a distributive referent on a
<- container is
<- the same as making all the statements about each of the members
<- separately.''
<- Now you might happily read RDF that I produced, and think that you
<- understood it.  However, you are turning all my disjunctions into
<- conjunctions, which will undoubtably result in problems.
<- Peter F. Patel-Schneider
<- Bell Labs Research
Received on Monday, 2 April 2001 12:47:03 UTC

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