From: Jos de Bruijn <debruijn@inf.unibz.it>

Date: Tue, 10 Mar 2009 10:28:57 +0100

Message-ID: <49B632D9.4010606@inf.unibz.it>

To: Dave Reynolds <der@hplb.hpl.hp.com>

CC: RIF <public-rif-wg@w3.org>

Date: Tue, 10 Mar 2009 10:28:57 +0100

Message-ID: <49B632D9.4010606@inf.unibz.it>

To: Dave Reynolds <der@hplb.hpl.hp.com>

CC: RIF <public-rif-wg@w3.org>

Dave Reynolds wrote: > Jos de Bruijn wrote: >> While trying to prove that the RIF Core version of the RDFS embedding I >> came up with [1] is correct, I found out that it is not. In fact, I >> believe it is not possible to embed all RIF-RDFS combinations into RIF >> Core in a straightforward manner. The problem is with rdfs:Resource. >> According to the semantics, every object in the domain is in the class >> extension of rdfs:Resource. This is naturally expressed using the rule >> Forall ?x (?x[rdf:type -> rdfs:Resource]) >> >> However, this rule is not safe. I see three ways of dealing with this >> problem: >> >> 1) disallow using rdfs:Resource in the rules and in RDF triples that are >> not of the form xxx rdf:type rdfs:Resource in the embedding >> >> 2) extending the embedding to define rules for all predicate symbols >> appearing in the rule set, e.g., if ex:p is a binary predicate, we add >> the rules >> Forall ?x ?y (?x[rdf:type -> rdfs:Resource] :- ex:p(?x,?y)) >> Forall ?x ?y (?y[rdf:type -> rdfs:Resource] :- ex:p(?x,?y)) >> >> 3) we drop the requirement of the rules being safe >> >> I would prefer option 1, because option 2 would make the embedding very >> complicated and I guess it is desirable to have the embedding in RIF >> Core (ruling out option 3). > > Something like option (1) seems like the best solution to me. However, > wouldn't you also need permit triples of the form: > > xxx rdfs:subClassOf rdfs:Resource I suppose such triples would not do any harm, so we could allow them. I was not aware, however, that people actually used such statements in practice. Jos > > ? > > Dave -- +43 1 58801 18470 debruijn@inf.unibz.it Jos de Bruijn, http://www.debruijn.net/ ---------------------------------------------- Many would be cowards if they had courage enough. - Thomas FullerReceived on Tuesday, 10 March 2009 09:29:45 UTC

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