From: Jim Hendler <hendler@cs.umd.edu>

Date: Mon, 1 Apr 2002 16:09:15 -0500

Message-Id: <p05101506b8ce7979a0b1@[10.0.1.4]>

To: www-rdf-logic@w3.org

Cc: sowa@bestweb.net

Date: Mon, 1 Apr 2002 16:09:15 -0500

Message-Id: <p05101506b8ce7979a0b1@[10.0.1.4]>

To: www-rdf-logic@w3.org

Cc: sowa@bestweb.net

Quotes from a message from John Sowa: > > Without logic, a knowledge representation is vague, with no criteria > for determining whether statements are redundant or contradictory. > Without ontology, the terms and symbols are ill-defined, confused, > and confusing. And without computable models, the logic and ontology > cannot be implemented in computer programs. Knowledge representation > is the application of logic and ontology to the task of constructing > computable models for some domain. while this is true, it doesn't mean the logic must be explicit in the language, just that their must be a formal model underlying the language -- thus, if I say X is in class Y and Y is in class Z. There could be an underlying model that entails the belief that X is in class Z, without my needing to be able to express the transitivity rule directly in the surface language. > >I agree with the following comments by Bill Andersen: > >BA> So, how well has the schema done for us? Not well. And it CAN'T do >> better -- its syntax and semantics don't have enough power. Of >> course one could try to encode all of this somehow in some arcane >> syntax that someone is going to have to interpret as doing what logics > > already do. The RDF and RDF-Schema efforts are just such encodings. Nonsense (who taught this guy Andersen's AI classes??? :->)! When you write classical logic with all the usual symbols it is meaningless scrawling on a piece of paper until we have the social agreement about how the symbols map to mathematical concepts. Similarly <ImplicationRule> <Antecedent> x </Antecedent> <Consequent> y </consequent> </ImplicationRule> is not something to "interpret what logics already do" but a means of encoding a particular bit of logic, assuming a social agreement as to what the meaning of this RDF is with respect to some mathematical model of entailment. > >I also agree with the following: > >BA> That said, WE SHOULD NOT fool ourselves that any of these quick fix >> tools (RDF(/S), XML(/S), DAML) are going to solve the real problems >> of (applied) ontology, let alone the two relatively easy ones I >> mentioned above. The long range solution to problems of data and >> information system integration depend on their solution. > >I would add that such XML-based tools can be used to encode a suitable >ontology, but only *after* some suitable logic-based tools are used to >define it. My major complaint about much of the work on the semantic >web is that people have drawn their diagrams to show that logic is built >on top of XML and RDF. I would turn those diagrams upside-down to show >that a suitable logic-based methodology is necessary *before* you can >begin to use RDF effectively. > But John, you yourself know that there is a clear difference between the encoding and the logic - so how can you make such a ridiculous claim. Of course there must be an underlying logic -- but that logic doesn't need to be expressible on the web to be useful -- the underlying logic below DAML+OIL, for example, can be expressed in KIF (see the axiomatic semantics [1] ) or Model Theory (see the semantic model [2]) The confusion is that the term "logic" on the layercake diagram doesn't mean "there exists a logic" it means "there is a formal logic, expressible on the web, embedded properly in web architecture (i.e. URIs and the like), and able to passed between web entities via proper protocols. These things are different than the need for a logic per se -- those are a dime a dozen and easily found in about 2000 years of literature -- heck your own books describe numerous of them -- just none that could be called a "web logic" at this point. cheers Jim H. [1] http://www.ksl.stanford.edu/people/dlm/daml-semantics/abstract-axiomatic-semantics.html [2] http://www.daml.org/2001/03/model-theoretic-semantics.html -- Professor James Hendler hendler@cs.umd.edu Director, Semantic Web and Agent Technologies 301-405-2696 Maryland Information and Network Dynamics Lab. 301-405-6707 (Fax) AV Williams Building, Univ of Maryland College Park, MD 20742 http://www.cs.umd.edu/users/hendlerReceived on Monday, 1 April 2002 16:09:18 UTC

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