Re: CG: Principles of ontology

Anthony K. Sarris (
Fri, 5 Dec 1997 13:46:49 -0800

At 9:43 AM -0500 12/4/97, Tim Lethbridge wrote:

>I was very happy to read such a clear set of definitions of terms in the
>field of Ontology. However, I have one major comment: No mention was made
>of the types vs instances.

>An ontology contains types.

>This suggests that an ontology *only* contains types, and that all the
>things in the ontology are types. Although this might be a widely-held
>perspective, I would not want to see this entrenched in a definition.
>In my perspective, one must draw a clear distinction when defining the
>term 'ontology' between types and instances. Types are things that can
>have instances -- the ontology is describing a world in which instances of
>its types exist. However, I do not think it is reasonable to say that
>*relations* are types. A relation declares that mappings exist between
>the instances of one type and another -- but the tuples of a relation
>should not be considered a case of instances of a type.
>This is a point that I have had many arguments about, but the easiest way
>to think about it is to use a simple linguistic test:

Oh, good, language games^H^H^H^H^Htests!

>If T is a type and I
>is an instance of it, one should be able to say "I is a T". This would not
>hold if T were a relation and I were a tuple of T. For example imagine Tim
>and John are brothers. The ontology has type 'Person' and relation
>'brother'. However, my assertion is that the *mapping* between Tim and
>John (i.e. the tuple) is not an instance of 'brother', and hence
>'brother', the relation, should not be considered a type. This is because
>I cannot say 'The mapping between Tim and John *is a* relation' -- one can
>say that it is a *tuple* of a relation, but a tuple and a relation are not
>the same thing.

What if we call the relation "Brotherhood", and each of the mappings
between or among the tuples of the relation [from the tuple Tim to the
tuple John and vice versa] constitutes a role that one entity in the
relation plays with respect to one or more other entities in that relation.
John plays the brother role/is a brother of Tim and Tim plays the brother
role/is a brother of John. But there's still this type called "Brotherhood"
that is a relation. It exists eternally in the land where types live.
There's also the particular instance of the brotherhood relation that
exists between Tim and John. It came into existence at the moment [given
one of the two males, John or Tim, already existed and] the second of the
two was born (assuming other criteria such as the same genetic parents or
an equivalent legal surrogate of that condition, such as represented by an
adoption). Technically speaking, when one or the other of Tim or John
dies, that instance of the brotherhood relation won't exist anymore, except
in a historical or hypothetical context.

>People argue with me

I just argued with you. I guess that makes me a person.


Tony Sarris