# Re: SEM: Layering

```Mike,

I should add my apologies to Pat's for having missed your message

http://lists.w3.org/Archives/Public/www-webont-wg/2002Apr/0200.html

I, too, like it.

I comment on whether <false> is a useful RDF graph, extending the analysis.

I think this message ends up very much in agreement ... (see end of
message).

I start from:

Michael K. Smith:
>We can be pretty sure this relation will not hold.  Consider for example
Pat
>Hayes' OWL:NIL element to terminate OWL lists.  If OWL uses OWL:NIL to
>terminate a list, then RDF with elements beyond an occurrence of OWL:NIL
>would have no interpretation in OWL and we would not expect even a simple
>syntactic round-trip to work.

>Going from the RDF

> x rdf:_1 a
> x rdf:_2 OWL:NIL
> x rdf:_3 b

> to OWL and back will yield

> x rdf:_1 a
> x rdf:_2 OWL:NIL

I had imagined this slightly differently.

I see your first graph as having exactly the same status in OWL as any other

a owl:differentIndividualFrom a .

I think of these as simply false (in OWL). In terms of the mappings T and
TINV this is special. TINV of either of your RDF graph above yields
(owl)false. Then T((owl)false) is (rdf)false. This is the only way of
getting falsity in RDF, by using a layer with the concept of contradiction.

As always false entails everything (both rdf-entails and owl-entails).

I hope for
T(TINV(rs)) entailing rs.

by defn this works in the bad cases (such as the one you picked out).
Taking the RDF triples above to OWL gets to false, going back to RDF is also
false, which entails the place we started from.

In terms of Mike's discussion of:

>SEMANTIC PROPERTY 1.

>  If RDF-ENTAILS(c,d) then OWL-ENTAILs(TINV(c),TINV(d))

and

>SEMANTIC PROPERTY 2.

>  If RDF-ENTAILS(T(a),d) then OWL-ENTAILS(a,TINV(d))

I think my analysis gives practically the same results, although I support
(SP1) & (SP2) rather than just (SP2). The difference is in the cases where
Mike's analysis does not allow (SP1) my analysis says TINV(c) = false, and
(SP1) holds trivially.

It's a different way of looking at it; quite probably not important.

Jeremy
```

Received on Friday, 26 April 2002 05:09:42 UTC