Re: What are the differences between the terms, CANDIDATE KEY, PRIMARY KEY, SUPER KEY, COMPOSITE KEY?

Marshall Spight wrote:
> Mikito Harakiri wrote:
> >
> > There is no formal distinction between them. Therefore, let's speak of
> > unique key or just a key. Formally, a key is a functional dependence
> > from a set of attributes to the whole relation header.
>
> This is nice and simple, but it slightly bothers me that in most cases,
> this describes an FD that has attributes on both the left and right
> side of the arrow. (Not that there is anything wrong with that, but
> perhaps there is some value to excluding the trivial depedencies?)

I think you have it backwards. A trivial FD is

header -> any set of attributes

not

a set of attributes -> header Received on Fri Feb 24 2006 - 19:44:29 CET