# Re: Two-valued logic

Date: Tue, 30 Dec 2003 07:25:51 GMT

Message-ID: <3M9Ib.11648$lo3.1065_at_newsread2.news.pas.earthlink.net>

> I work with a model that uses a two-valued logic. A NULL value under this

*> scenario can be handled logically as a null set value. With this model, a
**> NULL then = a NULL because a null set equals a null set..
*

Is your use of the indefinite article ('a two-valued logic') significant - that is, does the model you work with use one of a number of possible two-valued logics, but by implication not the familiar Boolean (Aristotelean) logic? (I'm just nit-picking, unless the answer is that 'a' is significant - but then I'm very puzzled!)

> My impression from reading Date and others is that the three-valued logic of

*> SQL that is proliferated in RDBMS's does not have a lot of fans. However, I
**> don't know if that is really the case or if I just happen to be reading the
**> pro-two-valued logic folks.
*

> Who is out there that will still defend three-valued logic within databases

*> and suggest that it is a better strategy than using a two-valued approach?
*

> Would it be accurate to state that most database theorists agree that a

*> two-valued logic provides significant benefits?
*

The proponents of 3-valued logic argue that the performance benefits claimed for 2-valued logic over 3-valued logic are over-stated. I've not done the experimentation to justify that. The clarity of 2-valued logic is better than 3-valued logic. The rules (and things like tautologies) are more familiar, so people would probably make fewer mistakes using a 2-valued logic. And when an empty set is appropriate as the 'unknown' answer, using an empty set instead of a third logic value would be a lot more sensible.

-- Jonathan Leffler #include <disclaimer.h> Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com Guardian of DBD::Informix v2003.04 -- http://dbi.perl.org/Received on Tue Dec 30 2003 - 08:25:51 CET