From: Peter F. Patel-Schneider (pfps@research.bell-labs.com)
Date: 11/30/01
From: Pat Hayes <phayes@ai.uwf.edu> Subject: Re: Can one layer a DAML+OIL model theory on top of RDF? Date: Thu, 29 Nov 2001 18:28:18 -0600 [...] > >I don't think that it is possible to create a DAML+OIL model theory that is > >both 1/ based on the RDF graph abstract syntax and 2/ compatible with the > >new RDF model theory. > > OK, I see your point. But this problem has nothing particularly to do > with the MT itself, right? It would probably be true with *any* MT > for RDF, since it arises from DAML's use of rdf:parseType to encode > DAML syntax. There is no way that any semantics for RDF can > accomodate in a principled way any ad-hoc use of RDF structures to > encode meanings, any more than a semantics for LISP can encode the > meanings of everything implemented in LISP. Yes, but parseType is not involved. Think of parseType as a macro, so the real surface syntax is a list. However, this list is just triples, and these triples are given interpretation in the RDF model theory. > > I say this because the triples generated by > >DAML+OIL logical constructs add extra stuff to models and this extra stuff > >gets in the way of entailment. (This is similar to the case argued a while > ago concerning arbitrary booleans in RDF.) > > We can patch this by invoking the distinction between asserted and > nonasserted triples. Possibly. However, I am opposed to any use whatsoever of this mechanism. > However, I think that if this is seen as a problem, then the real > cure is to be found by modifying DAML+OIL rather than by modifying > RDF. As the DAML reference says, 'DAML+OIL exploits the rdf:parseType > attribute to *extend the syntax for RDF* '(my emphasis). No model > theory can be expected to track extensions to the syntax. In this > sense, DAML+OIL is not an extension to RDF: it is a different > language implemented in RDF. It would be better to just stop trying > to implement it in RDF, and let it be its own language which is a > genuine *extension* of RDF. Yes, but, again, parseType does not play here. My view is that DAML+OIL is a different language from RDF. As such it should have its own syntax. However, I also think that DAML+OIL should include RDF as a sublanguage. [...] > >For example, the last two examples would result in no (new) RDF classes. > >Their semantics would only be employed by enclosing class definitions, > >resulting in the appropriate extension for the class, and not in extraneous > >relationships in the RDF model theory. > > See above comments on nonasserted triples. > > > > >As I see it there are really (only) two possibilities: > > > >1/ Keep the RDF graph (i.e., triple) abstract syntax and use a > > separate semantic treatment, because of the issues above. This is the > > route currently taken by DAML+OIL. However, it is *not* compatible > > with the RDF model theory. > > > >2/ Keep the essence of the RDF model theory, but go directly from a > > different (tree-based) abstract syntax (such as an XML data model) to > > the model theory. > > > >In my view, the second approach is better. > > Yes, I tend to agree. Note however that this could be done, I think, > in a way that preserves XML-RDF meanings, ie the same MT would work > for RDF and DAML from within XML. > > Alternatively, perhaps we could modify DAML to be a more rational > extension of RDF, rather than using the barbaric daml:collection > trick, which I think everyone felt was only a stop-gap, right? I also think that this would be done. That is a model theory for DAML+OIL can be developed that is an extension of the RDF model theory. Moreover, the XML syntax for DAML+OIL can include RDF/XML both as a sublanguage (i.e., RDF/XML syntax is valid in this language) and as a sublogic (i.e., the DAML+OIL model theory on this sublanguage is the same as the RDF model theory). (I'm not sure which of the two paragraphs above this satisifes.) > Pat peter
This archive was generated by hypermail 2.1.4 : 04/02/02 EST