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Re: Entailment / Datalog Complete, Sound, Terminating / English Reasoning

From: Drew McDermott <drew.mcdermott@yale.edu>
Date: Fri, 23 May 2003 16:43:47 -0400 (EDT)
Message-Id: <200305232043.h4NKhl028581@pantheon-po02.its.yale.edu>
To: www-rdf-logic@w3.org


   At 22:12 22/05/03 -0400, Adrian Walker wrote:
   >I was surprised to learn that RDF reasoning appears to be very restricted, 
   >as in:
   >
   >  "...a more complex fact is expressed in RDF using a conjunction 
   > (logical-AND) of simple binary relationships. RDF does not provide means 
   > to express negation (NOT) or disjunction (OR). The expressive power of 
   > RDF corresponds to the existential-conjunctive (EC) subset of first order 
   > logic"   [http://www.w3.org/TR/rdf-concepts/]
   >
   >Surely, for RDF to function as useful service-finding glue in the Semantic 
   >Web, it should at least support discovery of resources by being able to 
   >walk arbitrary depth first- and second-order hierarchies/ontologies ?

   [Graham Klyne replied:]

   I think the strength of RDF 
   here is that it's agnostic enough about reasoning methods to be used with 
   any or all of these -- it lets us exchange information, but doesn't tell us 
   how to "think".

This is a strange statement.  RDF (and its accessories, such as OWL)
were specifically designed to impose strict limitations on what can be
said and what kind of reasoning can be done.  The general philosophy
was to make it impossible for an undecidable reasoning task to be
posed.  Adrian is quite right that large groups of people who want to
do things outside the RDF mold are forced to operate in a nonstandard
or quasistandard world.  Check the recent traffic on www-ws@w3.org
(the web-services mailing list) for examples of the contortions
required to make DAML-S approximate legal RDF.

   [Graham again (I've reordered these two snippets of his message):]

   There is work in progress to address the other capabilities you 
   seek:  informally, there's CWM and a number of other software developments 
   that use RDF.

CWM does not just use RDF.  It _extends_ RDF.  To use that extension
yourself, you have to use CWM; the official version of RDF is not to
be extended in that way in the foreseeable future.  It's a lot like
Microsoft keeping to itself certain features of the operating system
API so that only Microsoft people can take advantage of them ;)

-- 
                                             -- Drew McDermott
Received on Friday, 23 May 2003 16:43:52 GMT

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