Re: The BOOLEAN data type - What is really Boolean and what is not?

> > Since three valued logic is not Boolean ( there are a number of
> > different ways the logic operations can be written ( for 3VL-AND and
> > 3VL-OR and 3VL-NOT )), you have to decide on the particular operations
> > that you will allow and how the results will be calculated. Therefore,
> > the normal Boolean operations of AND and OR and NOT cannot and do not
> > work with three value domains.
>
> I am not sure I understand you.

You cannot define operators AND and OR on a 3-element set in such a way that all axioms of Boolean algebra are satisfied. Try to fill-out those two tables in such a way that axioms hold:

+ T F N

T ? ? ?
F ? ? ?
N ? ? ?

• T F N T ? ? ? F ? ? ? N ? ? ?

T=True F=False N=Null(or whatever) +=OR *=AND

Hint: The problem will be the existence of the inverse element...

--
Regards,
Damjan S. Vujnovic

University of Belgrade
School of Electrical Engineering
Department of Computer Engineering & Informatics
Belgrade, Serbia

http://galeb.etf.bg.ac.yu/~damjan/