- From: pat hayes <phayes@ai.uwf.edu>
- Date: Wed, 12 Feb 2003 16:26:51 -0600
- To: Seth Russell <seth@robustai.net>
- Cc: www-rdf-comments <www-rdf-comments@w3.org>
>Pat, > >The WG agreed: > > "The group overwhelmingly, unanimously supports that > we should, in principle, focus on addressing the > provenance use-case." [1] > >You said: > > "Well, its (literally) impossible to give a coherent interpretation > of reification which satisfies everyone. We had to choose one, > and we chose the one that seemed to support the existing use > cases that people felt strongly about. " [2] > >So can I assume that the subsequent choices of the WG did in fact >support the provenance use-case? Yes. >Then you say: > > "In the present set-up, the reified triple is required to mean > what it would mean if you de-reified it. It refers to the proposition, > not to the surface syntax. "[3] > >In the light of the above wouldn't it be more accurate to say that >the reified node refers to the stating of the proposition, and not >the proposition itself ? Yes, it would. There are two dimensions here, in fact, which are kind of orthogonal: stating/statement (what the subject of rdf:subject/object et. refer to) de re/de dicto (what the object of the reification vocabulary refers to) We chose the stating/de re combination. What this means, in brief, is this: if I write for example aaa rdf:subject bbb . then aaa refers to a stating (not a statement) and bbb does not refer to the syntactic subject of the triple in the stating, which might be a bnode or a uriref (de dicto)., but rather to whatever that subject refers to (de re). And similarly for rdf:object, etc. The stating choice was largely motivated by the provenance use case, and that is what your citation [1] refers to. The other choice was also based on consideration of use cases, but I do not recall clearly what they were. What this combination allows one to do is to state a relationship between a particular document and some entity which the RDF triples in the document are talking about. This was what was needed for the provenance use case, as I recall. >Now we all know that we cannot substitute in a referentially opaque >context [4]. >I don't follow the reasoning that gets us from there to your statement: > > "In a nutshell, :thinks isn't a relationship between > an agent and an RDF reification, so it can't be an RDF property. "[5] > >Could you elaborate that reasoning for me? Well, the choice of the de re semantics means that it is possible, in effect, to substitute into a reification context. It isn't technically possible in RDF since there is no RDF equality, but if you put together the intended semantics for RDF reification and those of say OWL, then the combination ... aaa rdf:subject bbb . bbb owl:sameIndividualAs ccc . entails aaa rdf:subject ccc . So reifications are not opaque; so they are not strictly a suitable choice for representing an opaque context, such as the object of :thinks: or :believes, etc. However, as I noted in an earlier reply to Tim, there are probably ways to use terms like :thinks in a referentially transparent framework and hack round the rare cases where this might give problems, like the Superman case. Whereas the choice of the de dicto semantics would have made the logic very much more complicated and much harder to use in the 'normal' case where all the agents involved share a common understanding of the names in use. Pat > >[1] http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0263.html >[2] http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0237.html >[3] http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0237.html >[4] http://gncurtis.home.texas.net/illisubs.html >[5] http://lists.w3.org/Archives/Public/www-rdf-comments/2003JanMar/0229.html > > >Seth Russell >http://robustai.net -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes s.pam@ai.uwf.edu for spam
Received on Wednesday, 12 February 2003 17:26:58 UTC