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

Re: What do the ontologists want

From: pat hayes <phayes@ai.uwf.edu>
Date: Fri, 18 May 2001 14:34:57 -0500
Message-Id: <v0421012cb72b271e2895@[]>
To: Sandro Hawke <sandro@w3.org>
Cc: www-rdf-logic@w3.org
> > Ditch RDF and layer a logic directly on XML?  Just a thought... the problem
> > is that it loses a lot of the work currently being put into the 
>Semantic Web
> > and being described using RDF, unless there's a well-defined 
>migration path.
> > But it would give much more flexible structures and a far simpler way of
> > denoting what has formally defined semantics versus what is simply a data
> > structure.
>I think that's RuleML (http://www.dfki.uni-kl.de/ruleml/).  They're
>trying to build logical expressions of various levels of
>expressiveness on XML.
>It might help explain RDF to say
>  <rdf:Description about="Aristotle">
>     <rdf:type rdf:resource="man" />
>  </rdf:Description>
>means exactly the same thing as
>  <rule>
>    <!-- no premise, this is a ground fact -->
>    <conclusion>
>      <constant>Aristotle</constant>
>      <constant>http://www.w3.org/1999/02/22-rdf-syntax-ns#type</constant>
>      <constant>man</constant>
>    </conclusion>
>  </rule>
>give or take some conventions about string literals, namespaces, and
>ordering of elements in a tuple (and the fact that I'm just guessing
>at RuleML's current syntax -- sorry guys).
> > The alternative appears to be to accept that RDF will be used as a very,
> > very verbose encoding of LISP cons cells; and that some part of those
> > structures might be used to represent something formal, but that a large
> > part will straight data structure, or be glue that could be encoded and
> > processed more easily using a richer syntax.
>Basically yes, but two quibles:
>1.  I think you over-estimate the fraction of the data in the universe
>    that is more than ground facts.

But there are many ground facts that cannot be put into simple 
triples, notably negations. Ground facts can get arbitrarily 
complicated in their syntax in some languages: check out ground DAML, 
for example.

And, while it may be true that the bulk of the total information is 
ground facts, (maybe even ground atoms) if you just count symbols, it 
is often true that these ground facts are only of use because they 
can be processed by a smaller collection of non-ground facts (ie if 
'rules' can be applied to them).

>2.  RDF is not necessarily verbose: the RDF syntax in the current W3C
>    spec is verbose, but other RDF syntaxes are much less so (eg n3,
>    as Jos de Roo pointed out).

I agree: the verbosity arises chiefly from XML rather than RDF 
itself. Has anyone suggested Lexical_XML? 
letter><letter>s</letter> like that. Its a really neat universal 
notation: you can describe it in itself!  (The proof is too long to 
fit in this message, however.)

Pat Hayes

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Received on Friday, 18 May 2001 15:35:03 UTC

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