- From: Dan Connolly <connolly@w3.org>
- Date: Fri, 02 Feb 2001 15:30:47 -0600
- To: pat hayes <phayes@ai.uwf.edu>
- CC: Miles Sabin <MSabin@interx.com>, 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. > 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. 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. -- Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Friday, 2 February 2001 16:31:05 UTC