Re: Fabian Pascal and RDBMS deficiencies in fully implementing the relational model

On Thursday 2006-06-08 15:14, David Fetter wrote:
> On Thu, Jun 08, 2006 at 05:21:07AM -0700, dananrg@yahoo.com wrote:

> on bag theory[1] and 3-value logic[2].  Until they come up with a
> testable system, or Hell freezes over, whichever comes first, Pascal's
> book will make a good companion on your shelf to books on
> Phlogiston[3] theory, or a decent doorstop, whichever you prefer.

I have encountered at least two commercial database products that declared
every column "NOT NULL".  I have always assumed that this was defensive,
preventing stupid programmer mistakes.

I recall reading somewhere that Codd proposed multiple flavors of nullity.
Are there theoretical proposals for databases with logical systems having
more than three values?