notes from today's JC telecon on rules roadmap and explicit equality and semantics

From: Benjamin Grosof (bgrosof@MIT.EDU)
Date: 06/24/03

  • Next message: Mike Dean: "rule test cases"
    Hi folks,
    Here are my notes from today's JC telecon:  whose topics were rules roadmap 
    and explicit equality and semantics.
    In-line'd below, and attached too for convenience.
    % notes from JC telecon 6/24/03
    % by Benjamin Grosof
    agenda planned:
    - update and status check on roadmap for V1
    - discussion on explicit equality in relation to semantics
    Michael Dean
    Benjamin Grosof
    Ian Horrocks
    Sandro Hawke
    Said Tabet
    Ora Lassila
    Stefan Decker
    Peter Patel-Schneider
    Gerd Wagner
    o Update and status check on roadmap:
    Benj:  let's try to move into a mode wrt roadmap with more definite schedules
    and make some decisions, e.g., decide on timing for syntax, semantics,
    use cases and requirements.
    Mike:  Yes.  I have some suggestions, will post them.
            Also would like to get back to requirements and use cases.
    Benj:  suggestion:  please integrate your suggestions into the earlier roadmap
    document that I posted in 3 versions, and with your earlier
    roadmap suggestions posting from that time.
    Mike:  OK, will plan to do that.
    Ian: does it make sense to move to a full set of documents
    (cf. WebOnt's set) immediately, or do some intermediate form that we can
    get some feedback on.  E.g., would like to see a single strawman document
    on it, with roughing out of syntax, semantics, how it relates to OWL.
    Benj: how about we begin by merging, with a bit more coherence, the
    RuleML V0.8 Horn LP XML DTD and abstract syntax, and Horn LP semantics
    draft, that we already have, and add a bit on the story of how it relates
    to OWL
    Action item:
    Benj and Said volunteer to do a draft of that,
    have it ready for discussion at the 7/8 JC telecon (2 weeks from now)
    o explicit equality
    Benj initial presentation (verbal):
    motivation:  overcome limitation of Unique Names Axiom (UNA) in
    Herbrand models only, esp. once we later introduce ability to
    specify negation and default reasoning
    -- to specify selective default distinctness
    - ex.:  specify joe and joseph are equal, or two URI's are equal,
    but all other names (e.g., fred, sue)
    are distinct (not-equal) from these and from each other
    it (say, the predicate ee) can be axiomatized via:
    - ee is transitive and symmetric
    - there's substitutivity of equals, for every predicate and logical function:
       . need to state this as set of axioms (i.e., overall axiom schema(s))
    need to dig up logic literature on how this is axiomatized for FOL and LP
    MIke:  similar to sameIndividualAs in OWL
    Ian:  can implicitly specify equality in OWL, e.g., via
    equivalence of cardinality-1 classes
    [There was then some more discussion]
    Benj:  summarizing where we are after that discussion:
    no one has raised any obstacle to the plausibility of the following story:
    - we can introduce explicit equality into the Horn LP rule language,
    and it will pretty much correspond semantically to equality in OWL-DL
    - and then we can extend that to default distinctness, when negation-as-failure
    / defaults are introduced later into the rule language
    - but we need to do our homework to dig up relevant theoretical results
    from the logical KR literature
    Sandro:  wrt possible objections to least Herbrand model semantics for
    Horn case:  a use case that distinguishes it from behavior of Horn FOL
    Ian: are we designing (1) a rule extension to OWL/DAML+OIL (say OWL-DL)
    or designing (2) a
    rule language that is compatible/overlapping with OWL/DAML+OIL?
    Benj: (2).  OWL-DL goes way beyond Horn.  For (1), what we know how to
    do from fundamental previous research is simply to move to FOL.  For
    (2), tho', can view it as an extension of roughly the Description
    Logic Programs or Description Horn Logic subset of OWL.  There are
    lots of use cases for (2), more than for (1).  (1) requires
    fundamental new research if it's anything other than FOL.
    Sandro:  would like to be clearer wrt even the distinction between
    (1) and (2).
    Mike:  objectives for a rules language that some have articulated include:
    - can we have a complex OWL class as RDF type, within a rule system?
    - can we kind of fill in the gaps in OWL-DL, e.g., property chaining?
    Ian: i.e., some hoping from us to get "a better OWL", tho' that may
    not be very realistic
    Benj:  can approach this as follows:
    - permit rules in Horn FOL or Horn LP as well as ontology axioms in OWL-DL,
    then do inferencing in FOL or LP, then bring some of the conclusions from that
    back into OWL-DL
    - problem is that this is not well understood at a fundamental reasoning level
    Ian: e.g., should be straightforward to translate (OWL-)DL into a FOL
    theorem-prover, e.g., TPTP, e.g., using the CADE conference's competition's
    standard syntax
    - in preliminary experiments, a FOL theorem-prover can be reasonably efficient
    on DL axioms/tasks
    Benj:  then query it for DL expressions as queries,
    or to test overall consistency/satisfiability
    Stefan and all:  but this is not decidable
    Ora:  would like developers when getting rules too
    to still have a choice about using OWL-Lite or OWL-DL
    Mike:  how about we consider the computational processing model?
    Ian:  i.e., "how would we build one"
    Mike:  also, some test cases would help
    Peter:  it will definitely help to get a written proposal document on
    Ian:  don't want to have two different semantics, e.g., one LP and one FOL
    for next week, discussion of requirements and test cases
    - Mike volunteers to collect some
    for two weeks from now:
    discuss strawman document that Benjamin and Said will be drafting
    (others very welcome to help them!)
    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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