Re: Basic question?What 's the key if there 's no FD(Functional Dependencies)?

From: David Cressey <dcressey_at_verizon.net>
Date: Thu, 02 Nov 2006 12:50:27 GMT
Message-ID: <nQl2h.5889$OK3.1325_at_trndny09>


"paul c" <toledobythesea_at_dbms.yuc> wrote in message news:tOd2h.237313$5R2.133420_at_pd7urf3no...
> Brian Selzer wrote:
> > "paul c" <toledobythesea_at_dbms.yuc> wrote in message
> > news:pic2h.242958$R63.119230_at_pd7urf1no...
> >> Brian Selzer wrote:
> >>> <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???
> >>>>
> >>> A relation with at least one attribute *ALWAYS* has at least one FD.
> >>> Here are some of them for your example:
> >>>
> >>> {ABC} --> A
> >>> {ABC} --> B
> >>> {ABC} --> C
> >>> {ABC} --> {ABC}
> >>>
> >>> Note that all of the FD's are trivial.
> >>>
> >>>
> >> Wouldn't a relation with no attributes also have a trivial FD?
> >>
> >
> > I'm not sure: I've never thought about it. Is {} --> {} trivial?
Probably
> > so.

>

> Alright, I'll risk displaying my ignorance and ask if such a relation
> has exactly one FD, is there a way to count to two? (and thus three,
> four ...)
>

Before I go down this road... have you read up on DEE and DUM?

> p
Received on Thu Nov 02 2006 - 13:50:27 CET

Original text of this message