RE: Slides "RuleML Meets RDF" for today's Joint Committee telecon and RDF's bNodes

From: pat hayes (phayes@ai.uwf.edu)
Date: 11/11/02

  • Next message: Mike Dean: "Joint Committee telecon tomorrow 12 November"
    >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:danbri@w3.org]
    >Sent: November 5, 2002 4:54 PM
    >To: Boley, Harold
    >Cc: 'joint-committee@daml.org'
    >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>>
    >>
    
    
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