- From: pat hayes <phayes@ai.uwf.edu>
- Date: Tue, 3 Jul 2001 10:22:27 -0700
- To: jos.deroo.jd@belgium.agfa.com
- Cc: w3c-rdfcore-wg@w3.org
>that query thing is an interesting idea! >when we try to unify 2 anonymous nodes it is actually >like a query of one node against the other node >(the latter node looking like an in-line set of statements) >so the former one is existentially quantified >whereas the latter one is universally quantified >(and subjects match immediately (we use null's for them)) >and so everybody is right Well, you had better make sure that your unifications are all one-way. It is OK to instantiate an U-variable to an E-variable, but not the other way around. Pat Hayes >-- >Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/ > > > > > >Frank Manola <fmanola@mitre.org>@w3.org on 2001-06-29 07:19:07 PM > >Please respond to fmanola@mitre.org > >Sent by: w3c-rdfcore-wg-request@w3.org > > >To: Dan Connolly <connolly@w3.org> >cc: pat hayes <phayes@ai.uwf.edu>, w3c-rdfcore-wg@w3.org >Subject: Re: log:forSome/#rdfms-identity-anon-resources > >Dan Connolly wrote: > > > > Frank Manola wrote: > > > Dan Connolly wrote: > > [...] > > > > [[[ > > > > 4. A person is between a rock and a hard place. > > > > [...] > > > > > > > > Following is the KIF representation: > > > > > > > > (exists ((?x person) (?y rock) (?z place) (?w hard)) > > > > (and (betw ?y ?z ?x) (attr ?z ?w))) > > > > ]]] > > > > > > > > -- Conceptual Graph Examples > > > > http://www.bestweb.net/~sowa/cg/cgexampw.htm#Ex_4 > > > > Thu, 22 Mar 2001 01:45:12 GMT > > > > linked from http://www.bestweb.net/~sowa/cg/ > > > > linked from http://www.w3.org/DesignIssues/CG#[2] > > > > > > Yes, that was the interpretation I'd been assuming as well (see my > > > message > > > http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Jun/0326.html) > > > > Ah... good... then we're agreed, on the essential point. > >I'm not quite sure about that (as usual, the devil is in the details), >so I'm going to follow up a bit on your bookseller example. This may be >where my apology about barging in should really have come, since I think >I'm now bringing the discussion back to the point where Pat replied to >your bookseller example (I'll try to use different words though!) > > > > > [...] > > > > > So I don't understand how queries come into > > > this. > > > > Then never mind; somebody was convinced by the bookseller > > scenario about the need for existentials in RDF, so I thought > > I'd try it here. But I don't need the WG to agree with > > the bookseller/query scenario; only with the interpretation > > of triples as (exists (?a1 ?a2 ...) (and (p1 s1 ?a1) ...) ). > > > >The need for existentials is one thing; how they are interpreted is >another. Take your example: > > > In detail: let's suppose you're buying a book. > > You transmit, to the bookseller, a description > > of the book you want to buy; roughly, > > "it's by Barnsley and it's called > > Fractals Everywhere. I want it in > > hardback, tomorrow." > > > > Formally, in n-triples: > > > > ---8<--- > > _:g0 <http://purl.org/dc/elements/1.1/title> "Fractals Everywhere" . > > _:g0 <http://purl.org/dc/elements/1.1/creator> "Barnsley" . > > _:g0 <http://booksellers.example/vocab#binding> > > <http://booksellers.example/vocab#hardback> . > > _:g0 <http://booksellers.example/vocab#shipping> > > <http://booksellers.example/vocab#nextDay> . > > ---8<--- > >The problem is that in the interpretation of RDF triples we've been >discussing, if I ran across these n-triples on the Web, I should >interpret them, not as a request, but as an assertion that "there is a >book, which I'm calling -:g0, by Barnsley, with title "Fractals >Everywhere", in hardback, with shipping "nextDay" " (ignore for now >whether it makes any sense to talk about shipping in this context). If >I used Sergey's URI generation algorithm on this RDF, I'd substitute ><http://skolem.example#432oj34oij2o3ijo23j> for _:g0, so the assertion >would now be: "there is a book, which I'm calling ><http://skolem.example#432oj34oij2o3ijo23j>, by Barnsley, with title >"Fractals Everywhere", in hardback, with shipping "nextDay"; but the >essence of the assertion would be the same, only the name I'm now using >to refer to the book has been changed. > >The issue of context (or query vs. assertion) comes up in your example >when you send that RDF to the bookseller. If the interpretation of the >RDF as an assertion continues to hold, this would simply be a statement >to the bookseller that "there is a book...", to which the bookseller >might reply "that's nice" or "so what?". In this interpretation, it >doesn't much matter whether, in what you send to the bookseller, you >refer to the book locally as _:g0 or ><http://skolem.example#432oj34oij2o3ijo23j>. > >If the RDF is to mean a statement of requirements (a query), then the >interpretation is at least slightly different, and may be more >substantially different. The slightly different interpretation could be >something like "there is a book, which I'm calling _:g0, by Barnsley, >with title "Fractals Everywhere", in hardback, with shipping "nextDay" >", do you have one that matches? Changing _:g0 to the Skolem doesn't >change the essence of this situation; in this case the interpretation >of the RDF would be "there is a book, which I'm calling ><http://skolem.example#432oj34oij2o3ijo23j>, by Barnsley, ..." do you >have one that matches? The bookseller may have a book that *s/he* calls ><http://booksRus.example/inv2001-06-25#item342323> that matches the rest >of the description, and the problem is to decide whether > ><http://booksRus.example/inv2001-06-25#item342323> is the same book as >_:g0 on the one hand, or <http://skolem.example#432oj34oij2o3ijo23j> on >the other. > >[The situation is the same in a purer logic notation: the request might >say "there exists a book x, ..." and the bookseller's "fact base" might >say "there exists a book y, ..." and the problem would be matching x and >y; even if the bookseller's assertion was also "there exists a book x, >..." you would be unwise to assume that your x and the bookseller's x >were necessarily the same, without doing the rest of the feature >comparison, since the variable names come from different >namespaces/contexts.] > >In the more substantially different interpretation, you're not really >making an assertion about the existence of the book on your side at all, >you're asking the question "*is there* is a book, by Barnsley, with >title "Fractals Everywhere", in hardback, with shipping "nextDay"? [and, >if so, bind its identifier to _:g0]. Here, you really are interpreting >_:g0 explicitly as a true variable, rather than a local name, and asking >some process to determine bindings for it. And I would say this isn't >quite the same as saying that _:g0 is an existentially quantified >variable in a logical assertion. > >In either case, you want what you're calling the book to be interpreted >differently in a query, because there you need to indicate which parts >of the description of the book are purely local/arbitrary and need not >match exactly, and which parts are essential descriptions of the book >you want. I.e., in the case of the query, you want to distinguish "what >I call the book" (which may differ between the requestor and the >bookseller, and thus need not match) from the title, author, etc., which >must match to satisfy the request (and a true variable, rather than a >local name, is a much more explicit way to indicate that). The reason I >think queries complicate the situation is that the additional meaning >you have in mind for the existentials in queries is beyond the strictly >logical interpretation of existentials in assertions. > >--Frank > >-- >Frank Manola The MITRE Corporation >202 Burlington Road, MS A345 Bedford, MA 01730-1420 >mailto:fmanola@mitre.org voice: 781-271-8147 FAX: 781-271-8752 --------------------------------------------------------------------- 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, 3 July 2001 13:25:34 UTC