Re: Two-valued logic

"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message <news:bsnp6q$fdn$1_at_news.netins.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..
>
> 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?

At one point, Codd argued for a five (or more!) valued logic, with at least three Martian values used to denote "unknown", "not applicable", or "TBD" attributes. A better way is to split "nullable" fields off into separate tables and harass DBMS vendors to improve join performance. If they would just realize that separate "tables" need not be separate under the hood... Of course, now what does one do about "outer" joins? Better bug the vendors about UNION too while you're at it!

--
Joe Foster <mailto:jlfoster%40znet.com>  DC8s in Spaace: <http://www.xenu.net/>
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