On Monday 12 February 2007 14:46, Pat Hayes wrote:
> >On Feb 12, 2007, at 12:12 PM, Pat Hayes wrote:
> >>> You're right that import statements should not be considered part of
> >>> an ontology. I agree it's the imported axioms that are part of the
> >>> ontology.
> >>
> >> Wait. Of course the imports statements are part
> >> of the ontology. What are you guys talking about?
> >
> >*If* ontologies are logical theories
>
> Well, if "theory" has to mean deductively closed,
> then I would say no, they are not. That is, an
> ontology to me means a set of sentences (usually
> finite, usually not deductively closed) in an
> ontology language. Which is, roughly, a formalism
> with a model theory. (01)
I agree it seems to accord better with the way the term "ontology" is used to
think of an ontology (or at least the purely logical part of an ontology) as
the *axioms* of a logical theory, rather than as axiom+consequences (though
I'm not sure it matters much. (02)
> >, then it seems to me that this
> >confuses a mechanism for saying what (some of) the axioms of an
> >ontology are with the ontology.
>
> Why do you call this "confuses"? The assertion of
> what some of the axioms are can be part of the
> theory. You seem to be insisting on a 'levels'
> distinction here which I fail to see the reason
> for (and plenty of reasons to reject.) BTW, Cyc
> has been doing this for years. (03)
Come on, Pat, no one suggested it can't be done. Here's why I said the two
are being confused. Intuitively, an ontology is about a certain domain, say,
faculty and admin at TAMU. The relevant objects, properties and relations in
that domain are indicated by the names in one's ontology language. If one of
the names is now a URL pointing to your ontology at IHMC, then, on this
intuitive understanding of what an ontology is, your ontology at IHMC becomes
part of the *subject matter* of my faculty and admin ontology. That seems
wrong; conceptually, at any rate, I think we *should* distinguish statements
expressing genuine domain knowledge with statements concerning the location
of relevant domain knowledge. So, while I am most certainly not "insisting"
on it, I am indeed suggesting that there is an important conceptual
distinction to be made here between "object-level" statements concerning the
entities, types, and relations of interest in the ontology
and "meta"-statements about the ontology itself, notably statements about
where certain object-level statement can be found on the web. (04)
But really, we're simply involved in a quibble here. The important (?) thing
is to have a consistent understanding of what an formal ontology is. (05)
> >Suppose I'm writing my ontology for
> >TAMU faculty and admin again, and you've got a nice higher-level
> >ontology for universities over there at IHMC. My statement "import
> >(reiterate, endorse, whatever) Pat's university ontology" is not part
> >of my ontology
>
> YES IT IS. Check out the specs. In both OWL and
> CL , the imports is a *sentence*, and the
> truth-recursions apply to it like any other
> sentence. (06)
Well hang on now; the issue isn't whether imports has a respectable model
theoretic semantics. *No one* has questioned that, least of all me. The
issue is what a formal ontology is -- and "ontology" is not to be found in
the CL spec (except somewhat extraneously in Appendix C), which IIRC was a
conscious decision on our part. Granted, OWL has an explicit definition of
what counts as an *OWL* ontology, but that won't do across the board, so
there is some question as to whether it is worth trying to identify a general
notion that works for any representational context. (07)
> >I'm not dogmatically wedded to the idea that formal ontologies are
> >logical theories of some ilk, but if you're right, and my import
> >statement is literally part of my ontology, then formal ontologies
> >are not (in general) logical theories,
>
> Well, it depends on what you count as a logic, I
> guess. Is CL a logic? Because CL has importing
> with a full model theory, (08)
Well, I certainly don't want to quibble about that either. FWIW, in general,
I do tend to think language+model theory is sufficient for calling something
a logic (CL in particular I think of as a Web logic, a logic for a new
generation, if you will ;-), but I have to admit I was thinking of logic in a
traditional first-order way in my comments in this thread. (09)
> cf. section 6.3 in the ISO final draft
>
> http://cl.tamu.edu/docs/cl/24707-31-Dec-2006.pdf
>
> See also lines E17 and E20 in the semantics table
> in 6.2. As I put quite a lot of work into
> getting this (I hope) right, I guess I am rather
> unwilling to admit that it is broken or
> irrelevant. (010)
None of this is to the point, Pat, as "ontology" is not defined in CL. (For
the record, though, I think you got the stuff on importation exactly
right. ;-) (011)
> >and we'd better get clear
> >about the connection between the former and the latter. You seem to
> >be favoring the idea that ontologies are rather more concrete than
> >I'd been thinking. Do you think it would be better to say that a
> >logical theory is only one of several components of an ontology?
>
> See above. Whatever we decide should be the
> definition of "ontology" (God alone knows why we
> need a definition, but...), it had better be the
> case that the 10,000 or so existing OWL
> ontologies turn out to be ontologies by our
> definition. (012)
I would have to agree with that. (013)
> Now, *they* are collections of
> assertions in OWL (or maybe the XML documents
> which encode those assertions, or the RDF graphs
> which encode..., etc.; choose your favorite
> encoding level). These are finite entities and
> their sentences satisfy semantic constraints
> which fully determine their meanings. And the
> 'imports' sentences that they contain are part of
> them, just as much as any other sentences. (014)
Well, I still have the concerns I first expressed above, that this is mixing
things together conceptually that should be distinguished. (015)
-chris (016)
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