Re: Constraints and Functional Dependencies
Date: Sat, 24 Feb 2007 20:47:55 GMT
"Marshall" <marshall.spight_at_gmail.com> wrote in message
> I hope no one will mind too much if I take a break from our
> usual sort of discussion and talk about database theory for
> a bit. I feel like free associating about functional dependencies.
> I like to consider a system under which there is only one type
> of constraint: a formula of first-order logic. That is to say,
> there are no uniqueness constraints, foreign keys, primary keys,
> etc., except as such can be expressed as FOL formulas.
> In a data management context, there is some value to restricting
> what we can quantify over as being only attributes of declared
> relations (whether variables or constants.) So, we can't express
> the "no-upper-bound" property of the natural numbers; they aren't
> a database table so we can't quantify over them.
> With such a system, a relation R with attribute a (which I will
> write as R(a)) having a as a foreign key into S(b) is expressed
> as follows:
> forall R(a): exists S(b): a = b
Nitpicking response: the above not only expresses the foreign key concept,
but also referential integrity.
I don't want to make a mountain out of a mole hill here. I just want to reach consensus, if possible, before considering the rest of your discussion. Received on Sat Feb 24 2007 - 21:47:55 CET