Marshall wrote:
> Okay, a while back we were talking about writing constraints
> in a language with aspects of the relational calculus, specifically
> the existential and universal quantifiers. The point was made
> that that's unnecessary; the calculus is no more expressive
> than the algebra.
>
> So it ought to be possible to write any constraint from the
> calculus in the algebra.
>
> Well, I'm having a hard time figuring out how to do it. Can
> anyone help?
>
> How does one write a functional dependency in the algebra?
> A foreign key?
>
>
> Marshall
>
I thought that one was easy, if FK is the set of 'foreign key'
attributes and A is the 'referencing table' and using an op like D&D
<AND>, then it's something like A{FK} <AND> B{FK} = A{FK}. (I like this
one because it's particularly easy to implement.)
Received on Sun May 20 2007 - 23:08:41 CDT
