Re: Functional Dependencies?

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.

-- 
Jonathan Leffler                   #include <disclaimer.h>
Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com
Guardian of DBD::Informix v2005.02 -- http://dbi.perl.org/