Re: Functional Dependencies?

From: paul c <toledobythesea_at_oohay.ac>
Date: Sun, 02 Oct 2005 23:22:43 GMT
Message-ID: <7ZZ%e.58734$tl2.33476@pd7tw3no>

Jonathan Leffler wrote:
> paul c wrote:
>

>> I presume this is the same as saying that the attribute set, {}, is a 
>> key.

>
>
> Yes. Which, as others have said, indicates that there is at most one
> row in the relation - and, further, that there are no other FDs because
> any other FD necessarily has the empty set as a subset of the LHS
> (determinant) of the putative FD.
>

>> I wonder if the FD {X} -> {} means anything?

>
>
> Not really; it is a trivial FD since the RHS is a subset of the LHS of
> the FD.
>

thanks Jonathan - i owe you two now.

pc Received on Sun Oct 02 2005 - 18:22:43 CDT