notes from today's JC telecon 2/10/04

From: Benjamin Grosof (
Date: 02/10/04

  • Next message: Sandro Hawke: "reifying variables"
    % notes from JC telecon 2/10/04
    % by Benjamin Grosof
    Mike Dean
    Benjamin Grosof
    Sandro Hawke
    Ian Horrocks
    Peter Patel-Schneider
    Deborah McGuinness
    Drew McDermott
    Gerd Wagner
    Harold Boley
    Said Tabet
    Pat Hayes (joined late)
    o news:  OWL and RDF have become official W3C recommendations
    Sandro: the doc's are pretty much frozen, but in addition there is a
    process to collect errata and filter for which corrections are
    "normative" -- look near top of the top-level pages
    o Drew McDermott:  introducing DRS (see also his recent posting to sws-ig list)
    similar to the OWL Rules language, slightly different motivations and
    design decisions, thus hope they can evolve to converge.
    conjunctions are a class, and so on
    a regular formula is an object
    "disguises" atomic formulas or triples
    latest version can have SWRL near bottom-level in this regard
    DRS gives explicit quantifiers, unlike SWRL which has implicit outer
    universal quantifier
    invented it to represent planning, cf. PDDL
    students have extended it to use it for ontology translation
    Said Q: what would you like to see different/new in SWRL?
    Drew A:  liked the SWRL having an explicit class for variables, so changed
    to use that, can declare types, would like less tie to Prolog syntax
    wrt the above issue of implicit outer universal quanitifier,
    e.g., to have quantifiers or lambda binders for variables.
    E.g., in OWL-S sometimes preconditions have existentials.
    Benj:  the plan all along for future RuleML directions was to have
    explicit quantifiers, converged hopefully with SCL/FOL syntax,
    including to handle Lloyd-Topor kind of expressiveness in LP's,
    e.g., existential subexpressions in body or universal subexpressions
    in the head.
    Drew:  fine, agree with doing that, view the version omitting explicit
    quantifiers as simply shorthand for the version with explicit quantifiers.
    Benj:  so we could summarize by saying the time has come soon to put
    in explicit quantifiers.
    Ian:  yes, often find myself putting in explicit quantifiers to understand
    what SWRL rules say.
    (some discussion of planning and decision procedures and complexity)
    Ian:  we don't have a good fast procedure even for OWL-DL, much less SWRL
    of course one can use a generic FOL theorem-prover
    Benj:  so applications may want to avoid using too much OWL expressiveness
    in combination with rules
    Sandro:  what about putting OWL into a rule system?
    Ian:  see work by Raphael Volz where he did some experimental implementation
    including using DLP cf. WWW-2003 paper
    plus skolemizing and axiomatizing equality.
    He found quite a lot of what's in the DAML ontology library is in
    this expressive class, but much of this is legacy stuff from much simpler
    Benj:  as suggested in the DLP paper, those experiments
    show that use of rule system techniques can be advantageous in particular when
    there are large numbers of instance facts
    Ian:  if the non-instance ontology axioms don't change too often
    Harold Q:  are binary predicates -- which can map more easily/directly to
    RDF -- distinguished in DRS (syntactically) from n-ary predicates?
    Drew A:  not really;  could use type declarations to distinguish them
    (some discussion of dark triples;
    Drew:  just reify atomic formulas not everything)
    Sandro Q:  handling of variable declarations is a bit tricky in SWRL too,
    wrt interactions with general semantics of RDF
    Drew:  pretty much assume that you have an entire document and you can't
    take any subset of it -- don't like the RDF design spirit that wants to be
    able to take any subset of it and make sense of that
    Prof. Benjamin Grosof
    Web Technologies for E-Commerce, Business Policies, E-Contracting, Rules, 
    XML, Agents, Semantic Web Services
    MIT Sloan School of Management, Information Technology group or

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