Re: Codd's Information Principle

From: paul c <>
Date: Tue, 03 Nov 2009 22:55:49 GMT
Message-ID: <Vx2Im.50410$Db2.43141_at_edtnps83>

Bob Badour wrote:

> In logic, a relation is the extension of a predicate, and a predicate is
> the characteristic function of a relation. When talking about relational
> databases, sometimes one has to be clear about the internal predicate
> and the external predicate. At any given time, one will generally find
> fewer tuples in any relation variable than the internal predicate would
> allow because some parts of the predicate are not amenable to
> calculating or to expressing algebraically.
> ...

Do you mean certain negations and disjunctions aren't amenable, such as the predicate "it is not the case that the temperature T in city C is T degrees"?

(Thanks for the precision, still pondering the rest.) Received on Tue Nov 03 2009 - 23:55:49 CET

Original text of this message