Dear Chris, (01)
Could I attempt a slight precisification? I suggest: (02)
A formal ontology is a set of sentences in a formal langauge. (03)
I think an ontology covers a wider range of things, and the
addition of "formal" clarifies what we are really talking
about. (04)
Regards (05)
Matthew West
Reference Data Architecture and Standards Manager
Shell International Petroleum Company Limited
Shell Centre, London SE1 7NA, United Kingdom (06)
Tel: +44 20 7934 4490 Mobile: +44 7796 336538
Email: matthew.west@xxxxxxxxx
http://www.shell.com
http://www.matthew-west.org.uk/ (07)
> -----Original Message-----
> From: ontac-dev-bounces@xxxxxxxxxxxxxx
> [mailto:ontac-dev-bounces@xxxxxxxxxxxxxx]On Behalf Of Chris Menzel
> Sent: 19 January 2006 19:04
> To: John F. Sowa
> Cc: ONTAC Taxonomy-Ontology Development Discussion
> Subject: Re: [ontac-dev] What is "An Ontology"?
>
>
> On Thu, Jan 19, 2006 at 02:13:50AM -0500, John Sowa wrote:
> > I generally agree with Chris on technical issues,
>
> Ah, your wisdom knows no bounds, John! ;-)
>
> > but there are many unresolved practical issues about how to develop
> > and use the technology.
>
> Sure 'nuff.
>
> > So I'll add more qualifications and comments to some of the
> points in
> > this thread:
> >
> > CM> I prefer a nice, simple definition:
> > >
> > > An ontology is a set of sentences in a formal language.
> >
> > Yes, but. That says what it is, but it doesn't explain why anybody
> > would want one or what they'd do with it. I would therefore add the
> > following clause:
> >
> > "that is designed to characterize the entities of interest in some
> > domain for the purpose of representing, storing, and communicating
> > information about them and performing deductions and
> computations with
> > that information."
>
> I'm afraid I have to disagree if you want to include this in the
> *definition* of an ontology, as it turns a notion that is clear and
> precise into one that is fuzzy and indeterminate. On my proposed
> definition, there is always a definite answer, at least in
> principle, to
> the question: Is this an ontology? With your proposed emendation,
> before we can determine whether something is an ontology, we need to
> figure out what it was designed for, and the hopelessly intentional
> "designed for" relation is inherently neither precise nor determinate.
> Hence, with your emendation, it will often be the case that
> there is no
> definite answer to the question of whether something counts as an
> ontology.
>
> However, your point is well taken; I simply think it has to
> do with the
> important, but orthogonal, issues of quality and evaluation, not with
> the more formal matter of *definition*. Thus, I think your point is
> best made in accompanying *documentation*, wherein the simple
> definition would be glossed immediately with:
>
> Typically, ontologies are designed to characterize the entities of
> interest in some domain for the purpose of representing,
> storing, and
> communicating information about them and performing deductions and
> computations with that information.
>
> > >> What is the scope of an ontology?
> > >
> > CM> I don't know what "scope" means.
> >
> > I would say that it characterizes some domain of interest for some
> > purpose, such as developing and supporting applications that can
> > successfully use a significant amount of detailed information about
> > the entities in that domain.
>
> Sure thing -- good documentation! :-)
>
> > >> Do they change over time?
> > >
> > CM> No. Though of course one can trace change through an
> > > evolving series of ontologies.
> >
> > That is like asking whether a program changes over time. The answer
> > may be "no", but version 1.0 is typically replaced by v. 1.1, 1.2,
> > ..., 2.0, 2.1,....
>
> Just so, exactly my point.
>
> > >> How big is an ontology? How small can it be?
> >
> > I agree with Chris that the size is somewhere between 0 and
> infinity,
> > but for reasonable estimates, we should look at Cyc, which
> had about 2
> > million axioms about 2 years ago, and may have acquired a few more
> > since then. Most current ontologies are much smaller, but future
> > versions are likely to be as big or bigger.
>
> Right. I was giving the theoretical upper and lower bounds.
>
> > I agree with Chris that an ontology is a theory, not a lattice. But
> > it is possible to relate all the theories expressed in a particular
> > version of logic in a lattice. Each node of the lattice would be a
> > particular theory, and the theories could be related as
> > generalizations, specializations, siblings, or distant
> cousins in the
> > lattice. For more info about those issues, see
> >
> > http://www.jfsowa.com/logic/theories.htm
>
> Right, but theories are deductively closed on this approach,
> and I don't
> think we should identify ontologies with theories in that
> sense, as, for
> one thing, you can't distinguish between equivalent
> ontologies that use
> different axioms.
>
> Frankly John, I don't see the point of talking about the "lattice of
> theories" for a given language anyway. I think sometimes your talk of
> the lattice suggests that it is itself something might be usefully
> apprehended and studied. In general, however, there are uncountably
> many theories in such a lattice, so we will never be able even to
> apprehend one as an object of study except for the most technical and
> abstract purposes. Typically, all that's *really* useful to
> us are the
> possible logical relations that can hold between two *given* theories:
> equivalence, subsumption, compatibility, inconsistency,
> inconsistent but
> containing equivalent subtheories, etc. These relations of
> course would
> all be "pictured" by the lattice, but, again, typically, we'll never
> study the lattice per se, only specific nodes of interest and the
> particular logical relations they bear to one another.
>
> So I guess my point is that, for the most part, I don't think anything
> particularly useful is to be gained by talking about the lattice of
> theories for a given language in the context of ontological
> engineering,
> and that indeed it might engender more confusion than clarity.
>
> -chris
>
> --
>
> Christopher Menzel # http://cmenzel.org
> Philosophy, Texas A&M University # cmenzel@xxxxxxxx
> College Station, TX 77843-4237 # 979.845.5660
>
>
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