Path: utzoo!attcan!uunet!lll-winken!cert!netnews.upenn.edu!grad2.cis.upenn.edu!aaron
From: aaron@grad2.cis.upenn.edu (Aaron Watters)
Newsgroups: comp.databases
Subject: errors and 4-valued logic
Message-ID: <30999@netnews.upenn.edu>
Date: 11 Oct 90 13:48:07 GMT
Sender: news@netnews.upenn.edu
Reply-To: aaron@grad2.cis.upenn.edu.UUCP (Aaron Watters)
Organization: University of Pennsylvania
Lines: 29

In response to my brief account of one variety of 4-valued logic
where I claimed:

`the king of North America is bald' is error.

Chuck Phillips  writes:
:Clairification: A statement requiring the existance of the non-existant to
:be true, is simply false, not an error.  However, a domain violation _is_
:an error.  (e.g. "I am green years old.")
:
:If "king" is an out-of-band attribute, then the statement is an error; if
:"king" is within the defined domain, then the statement is simply:
:false.

Now I'm willing to admit that this may be what the Prophet Codd says, but
I respectfully disagree.

if ``The king of North America is bald'' is false then we infer
that ``The king of North America has hair'' must be true, right?

However neither statement can be meaningfully asserted to be true
because there is no king of North America.  My favorite
version of 4-valued logic resolves this difficulty by calling
both statements `overdefined' or `erroneous.'  I would argue that
treating either statement as having a truth value is 
actually illogical. -aaron.

PS: I also claim that `I am green years old' can reasonably be
treated as false.