Re: Web Rule Language - WRL vs SWRL

Jos de Bruijn wrote:
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> Jim Hendler wrote:
> 
> 
>>Jos-
>>that's not quite right as I understand it - to use an example from the
> 
> paper I cited -
> 
>>Given an ontology containing only a single RDF triple:
>><#pat> <#knows> <#jo>.
>>the answer to a query asking if pat knows exactly one person would be
> 
> "no" under
> 
>>RDF's open world semantics, but "yes" under the closed world semantics
> 
> of Datalog.
> 
>>there's no negation explicit here.
> 
> 
> If you would write down the query you mentioned, you would see that
> the query includes negation.
> 
> Fact is that a First-order theory:
> 
> knows(pat,jo)
> 
> entails only the fact:
> 
> knows(pat,jo)
> 
> 
> A Datalog program:
> 
> knows(pat,jo)
> 
> entails only the fact:
> 
> knows(pat,jo)
> 
> 
>>btw, this is not a small issue to me -- without some way to control
> 
> default reasoning (i.e. limit the scope of axioms and facts that are
> considered for a set of queries) there is just no way to link things
> reliably on the Web (and without the linking, why bother with Web).
> 
>>As far as I'm concerned, the minute one assumes there is a mechanism to
> 
> close a graph (and several are floating around), then ontology and rules
> go together just fine and lots of the layering is fixed. On the other
> hand, if a rule can be stated in general that has a negation as failure
> then we have a problem.
> 
>>In the old days, for example my thesis work, we used "ThNOT" in
> 
> langauges like MicroPlanner, NASL, etc. and that was some of the
> earliest work on this stuff. The idea was you could use a rule like this
> 
>>P :- ThNOT Q.
>>to mean P is true if you cannot prove Q. Implicit in this, and many of
> 
> the systems since, was the idea that there existed "A knowledge base"
> which was all the facts that this rule could be used on.
> 
>>On the Web, I would want this to read something like
>>P :- (Thnot Q) given R.
>>where "given R" somehow means with respect to some database, some
> 
> graph, or some other nameable and definable entity.
> 
>>Thus, for example, one could imagine running a query against some graph
> 
> (and note in theory that this could be the identity query, meaning it is
> equal to everything in the graph) and then stating that some set of
> rules is applied with respect to the resulting graph. These rules having
> NAF would be great and good and wonderful. If I applied your rules to a
> different graph, it would be up to me to decide if I wanted to restrict
> things in my graph to control the scope of the application of your rules
> -- this sounds like a powerful and crucial mechanism, and with it a lot
> could be done. Without it, rules on the web seem to me to either be just
> doing logic programming with a consistent syntax (in which case why
> invent all these languages, let's just use Prolog on the Web) or
> pretending the whole Web can be treated like a closed world - and
> that's, in my mind, where the dragons are...
> 
> It indeed seems like a good idea to define scoped default negation. We
> did not address this issue in WRL, but it would be a good topic to
> address for the W3C rules working group (if it's going to be formed).
> 
> 
> Best, Jos

I could not agree more and think that this could be a very useful 
extension of our current framework. Problably most of you need not to be 
pointed to a related thread some time ago on this list, starting with
  http://lists.w3.org/Archives/Public/public-sws-ig/2004Jan/0040.html
although it might be interesting to follow for those who did not...


best,
axel

-- 
Dr. Axel Polleres
Digital Enterprise Research Institute - DERI Innsbruck
Institute of Computer Science, University of Innsbruck
+43-512-507/6486               Axel.Polleres@deri.org
http://homepage.uibk.ac.at/~c703262/

Received on Wednesday, 22 June 2005 22:36:14 UTC