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re: facts of reality, context, possible worlds

From: Richard H. McCullough <rhm@cdepot.net>
Date: Fri, 6 Dec 2002 06:09:17 -0800
Message-ID: <002201c29d31$11848110$bd7ba8c0@rhm8200>
To: "Patrick J. Hayes" <phayes@ai.uwf.edu>
Cc: "RDF-Interest" <www-rdf-interest@w3.org>, "Richard S. Latimer" <latimer1@att.net>
I think our emails are getting too long (8 pages for the last one).  Therefore, I am temporarily ignoring most of the questions in your last email, and focusing on the most important issues.

1. RDF triples and facts of reality
a. I said
I tried to bridge the gap between the RDF document and the KR document by associating RDF "sets of triples" with KR "proposition list" with "facts of reality".
b. You said
I think that association might be mistaken, which may be giving us so much trouble. Certainly one should not identify RDF triples with 'facts of reality'.
c. My response
If RDF triples are not related to the facts of reality, then they have no value for anyone.  The purpose of the Semantic Web is to provide man and machine with easy access to the facts of reality.

2. context
a. I said
You are not getting rid of the context, you are making it explicit.
b. You said
Then it is no longer contextual. If I say 'it is raining' at 3 pm on 5 Dec 2002, then the time of my utterance is part of its context. If I say 'it is raining at 3pm on 5 Dec 2002', then my utterance needs no temporal context, and in fact it would be meaningless to ask what its temporal context was, ie when it was true. As far as time is concerned, it has been removed from the context space: its just simply true or false. Making information explicit *removes* it from the context.
c. My paraphrase of 2b
Context is all relevant knowledge not explicitly given in the statement.
d. the KR alternative
Context is all relevant knowledge, and is explicitly specified in the proposition.  The details of "proposition" are given in [1],]2].  For now, think of a proposition as
    at context { statement }
For this particular example, here is an outline of the context [3],[4] (you can add yourself to the context)
    at view=tabula rasa {
        definition of rain
        definition of fall
        at space=some city, time=3 pm on 5 Dec 2002 {
            rain do fall done

3. possible worlds
a. You said
Of course there IS only one world, but semantics has to be concerned not just with the way the world actually is, but with the ways that it COULD be given what we are able to say about it. It is impossible ever to say enough to pin down the actual world in full detail; and since a reasoner has no access to the actual world other than through sentences of the formal language, it has to as it were survey the possible ways that the world might be, given what is said about it. (You might find Tarski and Quine good authors to read on this topic, they both have the issues very clear. I speak of course as a disciple of theirs ;-))
b. My paraphrase of 3a
The real world is too hard, so we'll deal with imaginary worlds.
c. the KR alternative
It is not necessary to pin down the actual world in full detail.  You can select the appropriate level of detail, depending on your purpose, and express it in KR propositions.

[1] http://rhm.cdepot.net/doc/KRgrammar.txt
[2] http://rhm/cdepot.net/doc/KEtutorial.txt
[3] http://rhm.cdepot.net/kb/tabrasa.ku
[4] http://rhm.cdepot.net/kb/tabrasa.def    
Dick McCullough 
knowledge := man do identify od existent done
knowledge haspart proposition list
Received on Friday, 6 December 2002 09:09:21 UTC

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