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   Re: [xml-dev] Semantic Web and First Order Logic

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Bullard, Claude L (Len) wrote:

> Is it true or false that the semantic web
> limits the use of First Order Logic?

There is no single answer to that question.

As has been noted there are good reasons to restrict the formalism used to
model a problem, particularly that such restrictions, when properly made,
can greatly increase the speed of computations. The Web Ontology WG has
spent a great deal of time discussing such issues.

We've come up with 3 sublanguages of OWL, OWL Lite, OWL DL and OWL Full.


OWL Lite is the easiest to implement and guarantees the best worst case
reasoning performance.
OWL DL is a bit more complex to implement but guarentees that reasoning,
basically, can be performed in finite time.
OWL Full (which allows classes to be treated as individuals and hence is
'second orderish') makes no such guarentees on decidability nor
completeness -- though future work may allow this).

To be clear, RDF and RDF Schema are fairly unconstrained in what one can say
about what, and semantic extensions, such as N3/CWM are not necessarily
'first order'. For this reason, I wouldn't say that it has been decided in
any way shape or form that the Semantic Web need correspond directly to
First Order Logic (whatever the correspondance between a concept such as the
SW and a formalism such as FOL is intended to mean).




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