>Folks,
>
>I completely support Pat's discussion of closed worlds
>and open worlds. This is not a "debate", but a discussion
>of how to handle two kinds of databases, both of which
>are important for various applications:
>
> 1. Open worlds, such as information derived from
> observation, in which the absence of an entry
> does not imply its negation.
>
> 2. Closed worlds, such as information derived from
> an exhaustive enumeration or a declaration by fiat;
> i.e., anyone whose reservation has not been entered
> in the database does not have a reservation.
>
>Both kinds arise in many applications, and both must
>be supported. I also agree with Pat that the term
>"negation as failure" is misleading and that "negation
>by inference" is a better term.
>
>Once you adopt that term, you can begin to ask what
>kinds of inferences should be supported. Failure
>to prove (or observe) is a common basis for the
>inference, but there can be more subtle variations.
>
>For example, the fact that I haven't observed an
>elephant in my living room allows me to infer with
>high probability that no elephant is lurking there.
>But my failure to observe any bacteria in the living
>room does not imply their absence. (01)
Right. There is a fascinating line of research,
BTW, on inferences which people make intuitively,
seem to be surprisingly reliable, and seem to
have the general form "If x were y, I would know
about it; I havn't heard of x; therefore x isn't
y" This enables for example German students to
make reliable guesses about which American cities
are larger than others. I first heard of this in
the work of Gerd Gigerenzer on 'bounded
rationality'. See
http://en.wikipedia.org/wiki/Recognition_heuristic (02)
What I find fascinating is that this seems to
depend on there being just the right amount of
generally available public information, a lot but
not all of it. It wouldn't have worked in a
medieval society and it might not work in the
future for the opposite reason: people will all
know too much. (03)
>
>Having thrown in this bit of support, I'd like to make
>a brief comment on our argument about models and reality:
>
> 1. Pat prefers to identify the model with the thing
> that is modeled, except in circumstances when the
> thing modeled may not exist or may be difficult
> to observe in sufficient detail. (04)
That isn't how I would put it myself :-) (05)
> 2. I prefer to make a distinction between the two in
> all cases, but allow the option of saying that they
> may sometimes be identical or at least isomorphic. (06)
I will agree that an interpretation need not
*always* be made up of real stuff, as it were. In
fact it is easy to show that this is false: if an
ontology has any satisfying interpretations at
all, then it has a Herbrand interpretation
entirely made of symbols. My only point was that
it is *possible* to interpret ontologies directly
against the actual world (and this is often a
useful thing to do, if only as part of a thought
experiment.) (07)
>
>This reduces the debate to a question of relative importance
>or frequency.
>
>But there is one important reason for making the distinction
>between the model and the thing modeled: it allows the
>possibility of discussing and comparing different models and
>deciding which one(s) have a better correspondence with
>reality. (08)
Oh, sure. But here you are using "model" in what
I called the model-2 sense, right, rather than
the Tarskian sense used in "model theory". Then
this becomes the Korzybskian slogan that the map
is not the territory: which is true, of course. (09)
Pat (010)
>
>John
>
>
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