[RDF+OWL] Problem with coreifying RDFS entailment embedding

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).

Best, Jos
-- 
+43 1 58801 18470        debruijn@inf.unibz.it

Jos de Bruijn,        http://www.debruijn.net/
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Received on Tuesday, 3 March 2009 16:03:18 UTC