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Home -> Community -> Usenet -> comp.databases.theory -> Re: Two-valued logic

Re: Two-valued logic

From: Marshall Spight <mspight_at_dnai.com>
Date: Mon, 29 Dec 2003 00:22:18 GMT
Message-ID: <_sKHb.502995$275.1414945@attbi_s53>


"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..

I'm not sure I understand. Are you saying that your model includes the empty set? That seems sound if unremarkable.

> 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.

Most of the authors I've come across are critical of SQL nulls.

> 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 one person I respect who defends nulls is Lee Fesperman. He has a web site for his RDBMS product; there are whitepapers there that cover his reasoning.

His website:
http://firstsql.com/

"In Defense of Nulls"
http://firstsql.com/idefend.htm

For myself, I dislike 3VL, since I think it adds tremendous complexity but little expressiveness. The expressiveness it does add would be better dealt with in the type system, and not in the logic system.

Marshall Received on Sun Dec 28 2003 - 18:22:18 CST

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