Re: Foreign keys

On 2008-01-14 21:18:57 -0500, "Evan Keel" <evankeel_at_sbcglobal.net> said:

> Always a physical issue. Never a theory issue.Agree?

Foreign keys are functional dependencies across two relations.

More specifically, let

        R1(K1, A1, B1)
be a relation with attribute sets K1, A1 and B1 where K1 is R1's primary key and B1 is a foreign key to the relation

        R2(K2, A2)
where K2 is R2's primary key and A2 is the set of its remaining attributes.

Then the foreign key B1 represents the functional dependency

        B1 --> A2,
which is the functional dependency across two relation I mentioned in the first sentence.

Furthermore, through transitivity by the functional dependency K1 --> B1, the foreign key also represents the inter-relational functional dependency

        K1 --> A2.

Am I correct to say this?

-- 

-kira