Chris, (01)
>
>On Wed, 2009年10月07日 at 00:05 +0000, Len Yabloko wrote:
>> ...
>> Of course Semantic Web technologies are expanding now into these old
>> territories you have referenced with such detail and accuracy. But one
>> has to be very careful not to confuse semantic modeling with data
>> modeling and data linking with data integration. And, indeed, not to
>> confuse model-theoretic semantics (developed by Tarski for first order
>> logic and claimed by RDF) with various other semantics.
>
>By saying RDF has "claimed" model theoretic semantics, do you mean
>anything more than that it has been provided with a model theoretic
>semantics? That's a good thing, right?
> (02)
Right. And I wish that fact was not given more significance than a small step
forward in the right direction. By "claimed" I meant much broader claims made
subsequently about RDF-based tool's potential to solve semantic
interoperability problems. (03)
>> I believe OWL itself is an attempt to go around the inherent
>> limitations of Semantic Web.
>
>I'm not sure what limitations you have in mind. OWL is an attempt to
>provide a standardized ontology language built upon a logical framework
>in which questions of consistency, validity, etc are decidable. In
>general, such questions are not decidable, and that is certainly a
>limitation, but it predates the Semantic Web by several decades.
> (04)
The limitations are well-known and recognized by creators of Semantic Web.
Here is a good overview
http://www.ibiblio.org/hhalpin/homepage/publications/html/airedux/ (05)
And yes - some of it predates SW. But there are many claims that SW somehow
solves these problems, that somehow using SPARQL is solution to most of data
integration needs. (06)
>> I have been following these forum long enough to have heard all kinds
>> of claims about what is Semantics and many of these claims were tying
>> it directly to FOL, like no other logic or semantics ever existed.
>
>Really? I can't remember anyone ever having made any such claim. I
>frankly doubt whether you could find a single example. What people
>*have* said is that, whatever representational medium you choose, it
>must have a clear model theoretic semantics (regardless of whether it
>happens to be that of classical first-order logic) so that the meanings
>of its primitive logical vocabulary and its basic grammatical constructs
>are well-defined. Without that, questions of consistency and questions
>of whether one thing follows from another are, quite literally,
>nonsense.
> (07)
I don't want to get into this. Let's just say it was my impression. (08)
>I believe this is what Ed had in mind when he wrote:
>
>> >Formal logic is a means of expression, in which the basic elements of
>> >the language have well-defined meanings and a set of well-defined
>> >manipulations retain those meanings, and nothing more.
>
>I think by "well-defined manipulations" Ed means the inference rules of
>a logic -- whose legitimacy is justified by the underlying semantics.
>But, importantly, model theoretic semantics is very limited; it is
>restricted entirely to the assigning meanings to the basic logical
>expressions and telling us how to interpret the grammatical
>constructs of a language in terms of their simpler parts. For
>nonlogical vocabulary, a model theoretic semantics tells us only the
>*kinds* of things signified by each grammatical category: e.g., names
>refer to individual things (whatever those are), predicates refer to
>classes, etc. But *which* things the names of an ontology refer to and
>*which* classes its predicates pick out and exactly which classes a
>given individual belongs to and exactly what logical connections relate
>the classes we're interested in --- all of that is the job of what we
>might call "applied" semantics, a.k.a. ontology. And model theoretic
>semantics is entirely silent on those questions. As Ed put it:
>
>> >As to whether the snark actually is a boojum, classical formal logic
>> >offers only two possible interpretations: it is either true or it is
>> >false, and it cannot be both. And if you make a set of statements
>> >that allow the well-defined manipulations to produce a result of
>> >"true", then it does. That's all there is; there ain't no more.
>> >Formal logic is about "how to think"; it is not about what you think
>> >about.
>
>That is pretty much spot on.
>
>Chris Menzel
>
>
>
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> (09)
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