Re: Basic question?What 's the key if there 's no FD(Functional Dependencies)?
From: David Cressey <dcressey_at_verizon.net>
Date: Fri, 03 Nov 2006 12:05:53 GMT
Message-ID: <BgG2h.5563$WB4.5398_at_trndny04>
Date: Fri, 03 Nov 2006 12:05:53 GMT
Message-ID: <BgG2h.5563$WB4.5398_at_trndny04>
<saturnlee_at_yahoo.com> wrote in message
news:1162158876.794350.29460_at_f16g2000cwb.googlegroups.com...
> I have a basic question.
> Suppose there are 3 attributes: A,B and C.
> And there are no FD(trivial and non trivial )
>
> What 's the key for it? ABC or nothing???
>
Returning to the basic question.....
You can't avoid the trivial FDs. ABC ---> A; ABC ---> B; ABC ----> C; For that matter, ABC ---> AB.
Moving on. If ABC is a key and ABC is not a superkey, then ABC is the key.
If ABC is not a key, then "it" is not a relation. It doesn't matter whether you are talking math or data modeling. Received on Fri Nov 03 2006 - 13:05:53 CET