- From: Pat Hayes <phayes@ai.uwf.edu>
- Date: Tue, 6 Nov 2001 17:35:03 -0600
- To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
- Cc: Dan Connolly <connolly@w3.org>, w3c-rdfcore-wg@w3.org
>From: Pat Hayes <phayes@ai.uwf.edu> >Subject: Re: closing semantic issues >Date: Mon, 5 Nov 2001 12:13:46 -0600 > >[...] > >> > In particular, rdf:Bag is not a bag >> >at all, but instead is much more like a sequence. >> >> Right, and that is exactly how the M&S so describes it, by insisting >> that :_1, :_2 and so on apply to *all* containers. It would be easy >> to change the MT to describe a different notion than rdf:Bag, but >> then it would not in fact describe RDF. >> >> > If rdf is going to have >> >something called rdf:Bag, then its *RDF* semantics should conform to the >> >intended meaning of bags! >> >> Its model theory should conform to its intended meaning, but if that >> intended meaning is not in conformity with a broader notion of 'bag', >> then don't blame the model theory. What you are complaining about >> here is an issue in how RDF should treat containers, but its not a >> model theory issue. > >I'm not blaming the model theory at all here. However, I am blaming the >``theory'' of rdf:Bag as expressed in M&S. > >Let me restate my objection then: > >If RDF is going to have something called rdf:Bag, then its *RDF* semantics >should conform to the generally-accepted meaning of bags, and not to some >other meaning. I disagree. rdf:Bag is a class, is all. RDF is no more obliged to say precisely what it means than it is for any other class. >If the RDF semantics of this thing do not conform to the >generally-accepted meaning of bags then it should be given a different >name. My understanding of the situation was that the labelings rdf:Seq and rdf:Bag were intended to say simply that there were two classes of containers. All containers in RDF are treated alike, and are accessed in the same way *in RDF*. But something else, something outside RDF, might want to be told that one container should be thought of as bag-like, while another container, otherwise indistinguishable from it, should be treated as sequence-like. (There aren't any set-like ones, for some reason.) However, seen from within RDF, these are all simply containers. However, it seems that both you and Dan Connolly have decided that to call something a bag should mean that it really is a bag in RDF, in effect giving RDF some genuine datastructures. I take back what I said about it being easy to do, by the way. In fact, I don't see any way to do this in RDF. I don't think bags even make sense in a state-free language without recursion. We would have to have a non-numerically-indexed membership property for bags, :_inbag, say, so that to say that eg:bag contains a1 and a2 once would be saying eg:bag :_inbag a1 . eg:bag :_inbag a2 . However, there seems then to be no way to distinguish a bag from a set, since there is no way to say that a bag has two copies of something in it. It won't do to write the same triple twice; such a graph would be equivalent to the tidy version where you only said it once. If we were talking about programming, then the distinction would be between putting something into a bag once and putting it in twice, which makes sense; but we have no notion of 'put' in RDF. 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/~phayes
Received on Tuesday, 6 November 2001 18:35:11 UTC