From: pat hayes <phayes@ai.uwf.edu>

Date: Mon, 5 Feb 2001 23:30:56 -0600

Message-Id: <v04210125b6a53a914746@[205.160.76.246]>

To: Dan Connolly <connolly@w3.org>

Cc: www-rdf-logic@w3.org

Date: Mon, 5 Feb 2001 23:30:56 -0600

Message-Id: <v04210125b6a53a914746@[205.160.76.246]>

To: Dan Connolly <connolly@w3.org>

Cc: www-rdf-logic@w3.org

>pat hayes wrote: >[...] > > >4. RDF models can contain at most countably many statements: > > > becauce they're subsets of, >[...] > > > > Yes, you are right to infer that. However, your question raises > > another, related, issue: according to several members of the group > > which developed RDF, the 'graph model' of a set of RDF triplets is > > intended itself to be *the* model (in the sense from model theory) of > > those triplets. > >Really? can you cite a source for that? I'd like to correct it. > >The use of the term "model" in the RDF spec has >nothing to do with model theory, as far as I know. > >I think it was you, Pat, that explained that >what the RDF specs call a model is usually called >an abstract syntax in logic literature. Yes, I did, and when I had done so I got a phone call from Guha and an email from Ora (as I recall from memory: sorry if I am making the wrong attribution here) telling me why I was wrong, and that the right way to think about it was as I described above, ie that the graph model is, indeed, a model in the sense of model theory. It seemed kind of crazy to me also, but I wasnt there when this was decided, so I took it as authoritative (and gave up trying to make a model theory for RDF, since it already had one: a damn silly one, but then....) > > It follows that all RDF models of any RDF ontology > > (that could be stored on any web page, at any rate) must be not only > > countable, but finite. Now, since the finite-model restriction is not > > expressible in first-order (or any complete semi-decideable) logic, > > this would appear to indicate that RDF must have a semantics which > > has no semidecision procedure (and hence no proof procedure.) > >I'm just sort of teaching myself all this model theory stuff >as I go, but as far as I understand it, the semantics >of RDF are just like the semantics of first-order logic, >where the only terms are URIs (constant symbols) and >existentially quantified variables, and the only formulas are >ground propositions, conjuctions, and existentially quantified >formulas. > >At least, that's one logic, and it's sort of implicitly >in the RDF 1.0 spec. Yes, that is what I would have guessed from the spec; it is kind of what it suggests. I was trying to do was put reification into the model theory as well, which is trickier. Maybe I should get back to that task. >Things get more interesting when you start using the >RDF model/abstract-syntax with extensions to that >logic with stuff like =, not, KIF's wtr, lambda, etc. Er, yes, they would. Rather in the way that a pavement gets more interesting when the St Patricks Day parade walks on it. Pat --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola, FL 32501 (850)202 4440 fax phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayesReceived on Tuesday, 6 February 2001 00:28:04 GMT

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