- From: <jos.deroo.jd@belgium.agfa.com>
- Date: Fri, 15 Jun 2001 22:59:16 +0100
- To: bwm@hplb.hpl.hp.com
- Cc: Jan.Grant@bristol.ac.uk, w3c-rdfcore-wg@w3.org
Hi Brian, Great, I really find this interesting too! I think there are 3 kinds of variables [1] free variables [2] existentially quantified variables [3] universally quantified variables and I think the misunderstanding is that anonymous resources are (sometimes) 'treated' as [1] whereas I think they should always be treated as [2]. If somebody writes the following .nt _:a <uriref1> <uriref2>. and says that this is a statement, then (s)he is basically talking a free variable (somewhere floating around in triple space) I think this is wrong because there is no quantification: the floating thing should be existentially quantified and I think the best way to do that is to *point* to it. That can be simply done with a statement *using* that term e.g. <uriref3> <uriref4> _:a. or it can be done with <scope-uri> <the-log-forSome-uri> _:a. I have recently experimented with implicit scoping, but I think this is not a scalable approach. If we have terms existentially quantified, then I think that a lot can be done with such terms, but that's another topic... -- Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/ Brian McBride <bwm@hplb.hpl.hp.com> on 06/15/2001 07:46:30 PM To: jos.deroo.jd@belgium.agfa.com cc: Jan.Grant@bristol.ac.uk, w3c-rdfcore-wg@w3.org Subject: Re: log:forSome (Was: Model-specific identity for anon resources, and its representation: A new issue? Hi Jos, With regard to the recent discussion with Jan, I think there might be some miscommunication. What I think than Jan is saying is that, given the model: <http://descr1> <http:/prop> _:anon . <http://descr2> <http:/prop> _:anon . it is not possible to express this exactly in the RDF/XML syntax. The reason is that the only way this can be done is to assign an ID or a URI to the anonymous resource. That 'resource' then ceases to be anonymous. In effect, it is no longer a variable. Try translating the above n-triple example to RDF/XML and you will see what I mean. Reading your message again, maybe I get an inkling of what you are saying. We are talking here about what is an anonymous resource. We have been saying that it is an existentially qualified variable. I have been understanding that to mean that it denotes some specific resource with certain properties, i.e. _:anon <rdf:type> <rdf:Class> . says there is some specific resource, _:anon, which has type class. Is that what you would call a 'constant'? Ah. This is beginning to make sense to me. If it were a constant, then you wouldn't mind at all that a URI had been assigned to it. That would not change its nature. I think you may be saying that what I thought of as a variable is not really a variable. It does not bind to multiple values. Instead it represents a single value (constant) though I don't know what the value is. Hmmm. Now consider: 5+x=1 Is x a variable? No. Its an unknown, until I solve the equation. Have we been calling anon resources variables, when we should have called them unknowns? If what I previously thought of as a variable, is not really a variable, how would you explain what a variable is, without having to refer to concepts defined in a logic layer above rdfcore? This is really very interesting. Have a good weekend. Brian jos.deroo.jd@belgium.agfa.com wrote: > > > > I think/hack that both anonymous *terms* can be *unified* > > > which is NOT the same as equality > > > > Then your hack only seems to works when we can unify anonymous > > terms, or they have some sort of UniqueProperty attached. How do > > we solve the general case? > > There was some related discussion in the telecon > this afternoon, and I was kind of unable to explain > my point...(I'm really hopeless in that respect) > > The thing about anonymous nodes is that they > are ***variables*** > if they would be constants, we would be able > to identify them with ***URI constants*** > Now they are actually existentially quantified > variables, something like: there exists an _:a > or (using existing vocab): this log:forSome _:a > So I think we should say that *explicitly* > is the testresults (and in the model theory) > (the general case?) > > -- > Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/
Received on Friday, 15 June 2001 17:01:44 UTC