Semantic Web KR

From: Harold Boley (
Date: 03/18/03

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    Hi JC Colleagues,
    Peter started today's discussion on using OWL in its favorite (perhaps XML-based)
    syntax and using subClassOf of RDFS for encoding the DL-generated class hierarchy
    in a second document type. Both can be regarded as 'terminological documents'
    (T-Docs, webized T-Boxes).
    As we had discussed earlier (,
    RuleML derivation rules (e.g., webized Horn rules) can then access such an RDFS
    class hierarchy, via urirefs, for variable typing. 
    Similarly to a DL classifier generating an extensional class lattice from a set of
    intensional class definitions, a (bottom-up/forward) rule engine generates instance
    descriptions / facts via derivation rules. Both facts and rules can be regarded as
    'assertional documents' (A-Docs, webized A-Boxes) [although rules may also be viewed
    as separate 'inferentional documents' (I-Docs, webized I-Boxes)].
    A second link between the T-Doc and A-Doc layers is urirefs pointing from constants
    (often URIs) in instance descriptions / facts 'up to' the extensional class lattice,
    e.g. via rdf:type.
    Finally, Benjamin's and Ian's description logic programs explore direct connections
    between derivation rules and intensional class definitions.
    In summary, we get this picture:
        Intensional Class Definitions                 Extensional Class Lattice
        (in OWL, queried by DQL)       --generate-->  (in RDFS)
                  ^                                      ^        ^
                  |                                      |        |
      Description |                                      |        |
                  |        urirefs for typing variables  |        | urirefs for
            Logic |                                      |        | typing constants
                  |     ---------------------------------         |
         Programs |    |                                          |
                  |    |                                          |
                  |    |                                          |
     A-Docs:      v    |                                          |
        Derivation Rules                              Instance Descriptions / Facts
        (in RuleML)       ---------------generate-->  (in OWL, RDF, RuleML, DBs, ...)
    A version of this picture might help us keeping together the different KR communities
    and 'cultures' that have been developing languages for the Semantic Web.

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