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Re: Constraints and Functional Dependencies

From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 24 Feb 2007 14:41:36 GMT
Message-ID: <A8YDh.1112123$1T2.302035@pd7urf2no>


Marshall wrote:
> ...
> 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
>
> So we can express foreign keys this way.
> ...

I presume that if S had other attributes besides b, this definition would mean that b doesn't need to be a so-called primary key? (That would be okay with me.)

p Received on Sat Feb 24 2007 - 08:41:36 CST

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