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Home -> Community -> Usenet -> comp.databases.theory -> Re: Constraints and Functional Dependencies
mAsterdam wrote:
> A rephrase to (i) could be:
>
> <reference>
> (i a)
> A relation R with attribute a (written as R(a)) having
> a as a reference into S(b)
> is expressed as follows:
>
> forall R(a): exists S(b): a = b
>
> Note that b need not be a ck to S, hence 'into', not 'to'.
> </reference>
Does Marshall's notation S(b) mean that relation S has only one attribute b? If so then b is necessarily a ck (in fact the only key). If S(b) is actually a shorthand notation for S(b,b0...bn) then one can express that b is a ck by:
forall b: exists c0,...cn: forall b0...bn:
S(b,b0...bn): b0 = c0 ... bn = cn
Correct?
Keith - Fraud 6 Received on Sun Feb 25 2007 - 10:23:04 CST