Re: Constraints and Functional Dependencies

From: Walt <wamitty_at_verizon.net>
Date: Fri, 02 Mar 2007 21:39:16 GMT
Message-ID: <8Q0Gh.27$4u5.5_at_trndny09>


"Keith H Duggar" <duggar_at_alum.mit.edu> wrote in message news:1172420584.795179.172160_at_m58g2000cwm.googlegroups.com...
> 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).

Good point. I assumed that S(b) was the projection of relation S onto the domain of b.
But I didn't verbalize this assumption until I read your post, Keith. It's worth clearing up. Received on Fri Mar 02 2007 - 22:39:16 CET

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