From: pat hayes ([email protected])
Date: 11/11/02
>Dan, > >in the telecon the same issue was brought up. Currently RuleML doesn't have >a >particular representation for RDF's bNodes. We briefly discussed using >anonymous logical variables, empty or gensymed URIs, or an explicit >(builtin) >element. > >Looking at the RDF Model Theory edited by Pat, we are still open to various >possibilities for "simply indicating the existence of a thing, without >using, >or saying anything about, the name of that thing" >(http://www.w3.org/TR/rdf-mt/#unlabel). > >It now is clear to me that anonymous logical variables are no solution, >since >they are universally, not existentially, interpreted in facts. Doesnt that depend on the logic you are using? >For example, > >"bNode001 has creator Ora Lassila" > >cannot be represented as the Prolog fact ("_" indicates an anonymous Prolog >variable) > >has-creator(_,"Ora Lassila"). > >or the RuleML fact ("<var/>" indicates an anonymous RuleML variable) > ><fact> > <_head> > <atom> > <_opr> > <rel >href="http://dublincore.org/documents/dces/index.shtml.rdf#Creator"/> > </_opr> > <var/> > <ind>Ora Lassila</ind> > </atom> > </_head> ></fact> > >because it would mean that Ora created everything, e.g. making queries like > >has-creator("http://www.w3.org/People/DanBri","Ora Lassila"). > >or > ><query> > <_body> > <atom> > <_opr> > <rel >href="http://dublincore.org/documents/dces/index.shtml.rdf#Creator"/> > </_opr> > <ind href="http://www.w3.org/People/DanBri"/> > <ind>Ora Lassila</ind> > </atom> > </_body> ></query> > >wrongly succeed. > >I now think RDF's bNodes are more akin to some of the many uses of null >values in >relational databases or, perhaps, closer to RDF, in object-relational >databases. >A quick Google search revealed a related remark in "Topic Maps and RDF" >(http://www.isotopicmaps.org/pipermail/sc34wg3/2002-August/000495.html). > >Null values are absent from Prolog, but in Dagstuhl discussions with Jens >Dietrich >(http://www.jbdietrich.de/about.html) we thought they would be important in >RuleML >anyway (he is working on RuleML extensions for relational databases). Harold, please, calm yourself. They are just existential variables. Logic has had them since about 1878. > >So, to leave open the thing created we could assert >("<ind/>" would indicate a RuleML null value of type 'individual') > ><fact> > <_head> > <atom> > <_opr> > <rel >href="http://dublincore.org/documents/dces/index.shtml.rdf#Creator"/> > </_opr> > <ind/> > <ind>Ora Lassila</ind> > </atom> > </_head> ></fact> > >Yet, this would not give us the local existential scope of RDF's bNodes. >We hope our analysis of the RDF Model Theory will lead to a good solution >for >RuleML bNodes as well. > >Perhaps we should also have a closer look at eigenvariables in Lambda-Prolog >(http://www.cse.psu.edu/~dale/lProlog/). >Maybe we can even learn something here from the discussion of the "line of >identity" >in Charles Sanders Peirce's Existential Graphs >(http://users.bestweb.net/~sowa/peirce/ms514.htm). Lets not get crazy here. There isn't anything very deep or mysterious about existential quantifiers. Pat > >Ultimately, we may need explicit (existential) quantifiers for glueing >together >a conjunction (or a rulebase) of facts. > >Harold > > >-----Original Message----- >From: Dan Brickley [mailto:[email protected]] >Sent: November 5, 2002 4:54 PM >To: Boley, Harold >Cc: '[email protected]' >Subject: Re: Slides "RuleML Meets RDF" for today's Joint Committee >telecon > > > >Harold, > >One question re: > "RDF triples become special binary facts where the relation and >first > argument must be urirefs, and the second argument can be urirefs or > literals" > >Does RuleML have any particular representation for RDF's bNode (aka >'anonymous' or un-named resource) construction? > >Dan > >On Tue, 5 Nov 2002, Boley, Harold wrote: > >> Hi folks, >> >> attached are the slides "RuleML Meets RDF" for today's Joint > > Committee telecon. >> >> Please, if possible, have them in PPT 2000 presentation mode >> so I can go over them in the 30 minutes allocated by Mike. >> >> Harold >> >> >> >> <<ruleml-rdf.ppt>> >> -- --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell [email protected] http://www.coginst.uwf.edu/~phayes [email protected] for spam
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