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Re: [ontolog-forum] blogic iswc keynote

To: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: sowa@xxxxxxxxxxx
Date: Fri, 25 Dec 2009 13:54:01 -0500 (EST)
Message-id: <74e4ab6e0e17fea0e598195854bb5268.squirrel@xxxxxxxxxxxxxxxxxxxx>


I agree.

> "without negations" literally means without KNOWING EXPLICIT negations.
> Most DBs that get exception cases store them in a table like the one that
> caused the exception. So, in effect, there are tables of TrueS and Tables
> of FalseS - or "fluents" as some logicians like to call them. Therefore,
> negation is in fact modeled where appropriate in current DB practices.

Your note illustrates the point that a relational database
can be used to support various kinds of semantics.

The default way of using SQL is negation as failure:  each
table contains the n-tuples for which a relation is true.
Any n-tuple not listed is assumed to be false.  That is the
so-called closed-world assumption.  If the conditions of
that assumption hold, then negation as failure is the
equivalent of true negation.

But it's possible to use two tables per relation:  one would
contain all the n-tuples for which the relation is known to
to be true, the  other would contain all n-tuples for which
the relation is known to be false, and the truth value of any
n-tuple not in either table would have the truth value unknown.

With an appropriate front end, the RDB would support a three
valued logic:  known true, known false, and unknown.


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