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Re: [ontolog-forum] Executable English and Logic (Was: accounting inteop

To: "John F. Sowa" <sowa@xxxxxxxxxxx>
Cc: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
From: Pat Hayes <phayes@xxxxxxx>
Date: Sun, 11 May 2008 08:51:33 -0500
Message-id: <p06230906c44ca9074707@[192.168.1.2]>
At 10:26 PM -0400 5/10/08, John F. Sowa wrote:
>Adrian,
>
>  > Unfortunately, classical logic assigns a meaning to negation
>  > that differs from the way databases are actually used.
>
>That is true.  There are four widely used options:
>
>   1. The closed-world assumption (CWA) in which any ground clause
>      (n-tuple of constants) not asserted to be true is assumed
>      to be false.  This is typical of airline reservations:  if
>      your reservation is not in the DB, you don't have one.
>
>   2. The open-world assumption (OWA) in which any ground clause
>      not asserted to be true has an unknown truth value.  This
>      is typical of most databases generated from observations.
>      Anything not observed is not known to be true or false.
>
>   3. Three-valued logic (TVL) in which some ground clauses are
>      asserted to be true, others are asserted to be false, and
>      any others have an unknown truth value.
>
>   4. The whatever assumption (WA) in which anything not asserted
>      to be true may be false, unknown, or whatever.  This is the
>      widely used method of code-and-debug until you get tired
>      or the deadline has passed.
>
>
>  > Unfortunately, classical logic assigns a meaning to negation
>  > that differs from the way databases are actually used.
>
>Classical negation corresponds to the CWA.    (01)

I think you mean the OWA.    (02)

Pat
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