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