Re: A simplistic definition of "ontology"
phayes@ai.uiuc.edu (Pat Hayes)
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Date: Tue, 10 Oct 1995 12:54:19 -0600
To: "Nicola Guarino" <guarino@ladseb.pd.cnr.it>, "Eduard Hovy" <hovy@isi.edu>,
srkb@cs.umbc.edu, "Pat Hayes" <phayes@cs.uiuc.edu>
From: phayes@ai.uiuc.edu (Pat Hayes)
Subject: Re: A simplistic definition of "ontology"
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At 3:50 PM 10/10/95 +0100, Nicola Guarino wrote:
...
>
>Thinking better at the difference between the two positions, I don't see a
>BIG tension between Michael Gruninger's definition of a "glossary-ontology":
>
>>a coherent characterisation of a domain with the terms and their
>>inter-relationships carefully considered and defined.
>
>and the more logical definition I have proposed. Maybe I have being
>stressing too much the use of logic in my previous messages, but the crucial
>point, in my opinion, is not so much the use of logic, but the ability to
>discriminate somehow among external (real-world) "models".
But this kind of a definition seems to exactly fit a logical theory. Thats
what logical axioms ARE: characterisations of the domain(s) which are their
models by describing ways of discriminating between classes of models.
(What better a characterisation could you have?!). Your use of words like
"external (real-world)" begs an important question for KR. We begin the
whole enterprise by trying to write down knowledge about this real world.
The logical axioms purport to be a way of capturing it: but if their
meaning can only be explained by referring back to our intutitions, then
nothing has been achieved. (Here is a universal Ontology: it has the single
symbol P in it, which means whatever you intend it to mean, from time to
time.)
....
>Pat Hayes writes:
>
>> What one 'has in mind' is presumably expressed
>>there in some mental representation. Now, how do we know that this
>>mentalese representation in fact has unique models? .....
>Notice that, in the examples above, I am speaking (and thinking) of
>*concrete things* (configurations of pixels or blocks) these are the models
>(better, the states of affairs) I have "in mind"...
If you have a block literally "in" mind you need brain surgery. Our
thoughts consist of manipulations to mental symbols (in 'mentalese'), and
these symbols *denote* pixels and blocks.
But this is a philosophical byway, probably best not pursued here.
>
>A final comment regarding something I have not understood in Pat's words:
>
.....
>>>"An ontology is a *partial* specification of the intended *possible* models
>>>of a logical language"
>>>
>>
>>But then what else is that logical language itself?
>
>Sorry Pat, I am not able to see your point, could you expand a little bit?
Axioms written in a language with a semantic theory can be usefuly regarded
as restrictions on the set of models: the smaller the set of axioms, the
larger the set of possible interpretations. Now, how can we axiomatically
characterise the set of *all possible* models? Clearly, in the limit, its
characterised by the empty theory, ie by having no axioms at all, ie by the
semantic rules of the language itself. For example, we can usefuly regard
the inference rules of FOL as conventions which describe the set of
intended possible models: those rules 'fix' the meaning of the logical
symbols in a way that precisely conforms to the intended interpretation.
Since many interpretations are possible, this specification is correctly
described as *partial*,ie it doesnt specify a unique interpretation.
.... an ontology, on
>the other side, is a particular set of proper axioms used to restrict the
>models of the language in order to avoid (some of) the non-intended ones.
>
OK with me: but THAT definition of ontology is explicitly rejected by the
'glossary' perspective. Which is where we came in.
Pat
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