On 7/10/2012 10:27 PM, John F Sowa wrote:
> Your question can't be answered in one or two sentences.
>> My initial impression was caused by a revulsion to the underlying
>> assumptions [in Boris Motik's paper]. But I admit that it's not
>> a bad paper of its kind. [For anyone who likes that kind of thing.]
>> I ask if you have anything further to say about these "underlying
>> assumptions". They may go much deeper than the assumption that
>> logics used by the semantic web should be decidable, to the
>> *reasons* someone would have such a belief, i.e., the purpose
>> of these logics and their languages.
> For a brief history of semantic networks, see
> Early networks didn't represent logic very well. Bill Woods (1975)
> wrote a critical article called "What's in a link?" His student,
> Ron Brachman (1979), responded by implementing the Description Logic
> KL-ONE for his PhD dissertation.
> Brachman, Fikes, and Levesque (1983) combined KL-ONE with a first-order
> theorem prover in a hybrid system they called KRYPTON. They called
> the KL-ONE hierarchy and and its classifier the T-Box (terminology box)
> and the FOL statements and theorem prover the A-Box (assertion box).
> The T-Box and A-Box combination was widely adopted in many systems.
> The logic for the A-Box is usually much more expressive than the
> logic for the T-Box. For certain kinds of problems, a theorem prover
> for a typed version of FOL that uses a T-Box with hierarchy of types
> or sorts can run orders of magnitude faster than a theorem prover
> for an untyped version of FOL.
> During the 1980s, the DLs weren't very efficient as classifiers,
> and two schools of thought developed about how to improve efficiency:
> limit the expressive power of the T-box to a version of logic that
> could be computed more efficiently; or use hybrid methods that
> support different reasoning methods for different problems.
> Cyc is the world's largest formal ontology and reasoning system.
> Instead of just two components (T-Box and A-Box) it has multiple
> reasoning methods specialized for a wide variety of problems.
> For any particular problem, the system chooses an appropriate
> method automatically. See
> Fads and fallacies about logic
> The ability to let the system choose the reasoning method
> automatically can be, for many applications, more powerful
> and efficient than just relying on a single method.
>> While thinking that decidability is essential might not *itself*
>> be justly called a "disease", only wrong, there may also be
>> a more deep rooted notion about the relationship between people
>> and machines that would lead to thinking decidability was important,
>> and this fundamental notion that may be finding itself in conflict
>> with what is most practical.
> The simplest explanation is "To a man whose only tool is a hammer,
> all the world is a nail." Computational complexity is a subject
> that every computer scientist should know, at least at a basic level.
> But there are some people for whom decidability is their only tool.
> They repeated the decidability mantra until people who had no idea
> what it means began to believe it.
> Following is a quotation from Bob MacGregor (1991), who developed
> the LOOM and PowerLoom systems. He used the T-Box and A-Box
> combination and advocated a variety of methods:
>> There is a variety of evidence suggesting that a KRS (Knowledge
>> Representation System) with an expressive terminological language
>> (and an incomplete classifier) is a more useful tool than a KRS
>> with a small terminological language (and a complete classifier).
>> In this section, we present arguments in favor of implementing
>> an expressive ("promiscuous") terminological language, and also
>> propose an architecture that may turn out to allow us the best
>> of both worlds.
> A more common term today is 'heterogeneous' instead of 'promiscuous'.
> That is what Marvin Minsky has been recommending for years, and the
> evidence I've seen has convinced me that he's right.
> I have no quarrel with allowing people to choose a tightly constrained
> language such as OWL, if they find it useful for their problem. But
> the heterogeneous systems are much more flexible. That is what Tim B-L
> proposed in 2000:
> Tim B-L:
>> The goal of interoperability between heterogeneous components that we
>> build is one that will test the extent to which the Semantic Web is
>> achieving its promise. The more diverse the systems interoperating,
>> the greater the merit of the Semantic Web.
> See http://www.w3.org/2000/01/sw/DevelopmentProposal
> I never liked the use of XML for representing triples, but Tim also
> mentioned a wide range of other languages that could be supported:
> "Prolog, SHOE, Algernon and KIF". He mentioned triples, but he also
> mentioned relational databases.
> If Tim's view in 2000 had been accepted, I think that we could have
> had a great Semantic Web today. It could have become a powerful
> platform for developing logic-based applications. Instead, all
> that's left is an anemic combination of RDF(S) + OWL + SPARQL.
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