Re: [Person-ontology] D7 - Which languages are better than OWL?
Pat and Gian Piero,
The recent messages seem to be flying past one another without
making contact. I'd like to comment on some of the issues:
PH> What do you mean by a n-ary *situation* ? The situation
> being described has no intrinsic 'arity' (a point made many years
> ago by, I believe, Strawson), because one can go on adding
> qualifiers endlessly (he did it... at midnight... in the kitchen...
> last week... with a knife... silently... rapidly...). In fact,
> this has been used as an argument (to me, convincing) for the
> naturalness of the binary case-based representation over the use
> of n-ary relations.
GPZ> ... a dynamic situation like that represented by "Mary has given
> a book to Bill", you must introduce a predicate in the form of GIVE,
> MOVE or whatever, and take into account the fact that "Mary",
> "book-1" and Bill" - apart from being instances of ordinary concepts
> in a standard ontology - are also characterized by given logical
> relationships with this predicate.
Two points: First, linguists who talk about case roles distinguish
obligatory roles from optional roles. Second, the word "situation"
is notoriously difficult to define. In 1983, Barwise & Perry tried
to make situations the foundation for their theory of semantics.
For a few years, there was a strong current of activity dedicated
to that approach. But it came to grief over one serious problem:
Nobody was ever able to define the central term 'situation'.
In his 1991 book on situation theory, Keith Devlin wrote
"Situations... include, but are not equal to any of simply
connected regions of space-time, highly disconnected space-time
regions, contexts of utterance (whatever that turns out to mean
in precise terms), collections of background conditions for a
constraint, and so on."
After further discussion, Devlin admitted that they cannot be defined:
"Situations are just that: situations. They are abstract objects
introduced so that we can handle issues of context, background,
and so on."
John McCarthy faced a similar problem in trying to define contexts.
He finally gave up, in the same way as Devlin: he treated contexts
as undefined abstract objects.
For Devlin, situations are undefinable objects whose purpose is to
simplify the problems of reasoning about contexts. For McCarthy,
contexts are undefinable objects whose purpose is to simplify the
problems of reasoning about situations. The central issue in both
of those statements is the word 'purpose'.
That, in short, is the fundamental reason for the failure of
situation semantics: you can't derive propositional attitudes
from objective statements about what exists. Philosophers made
a similar statement about value judgments: "You can't derive
'ought' from 'is'." That point is true of every attitude.
Agents who have attitudes are the sources of attitudes. Among them
are values, purposes, intentions, etc. Consider the following two
descriptions of the same event:
Mary held a book. Bill took it.
Mary gave a book to Bill.
No observation can determine whether one statement is more accurate
or appropriate than the other. Their physical implications are
identical. But there are differences in attitudes: The first
sentence is neutral about ownership and the intentions of the
two agents. But the second sentence implies that Mary had a
right to the book, which she voluntarily transfered to Bill.
I agree with Pat (and Strawson) that it is possible to add any
number of qualifiers to any description of anything. But in any
statement that describes the attitudes (intentions, purposes, etc.)
of the agents, a certain combination of relations is obligatory
to the description. When those relations are omitted, the
attitudes of the participants are no longer adequately described.
And by the way, that is indeed a Peircean point. If Barwise,
Perry, and Devlin had read Peirce, they might have developed
a more successful theory.
John