Re: what are keys and surrogates?

From: vldm10 <vldm10_at_yahoo.com>
Date: Mon, 14 Jan 2008 13:11:35 -0800 (PST)

On Jan 14, 2:51 pm, "David Cressey" <cresse..._at_verizon.net> wrote:
> "vldm10" <vld..._at_yahoo.com> wrote in message
>
> news:8c40c81a-2278-4727-b3ae-158cdc87e8e2_at_q77g2000hsh.googlegroups.com...> On Jan 13, 4:41 pm, "David Cressey" <cresse..._at_verizon.net> wrote:
> > > "David BL" <davi..._at_iinet.net.au> wrote in message
>
>
>
>
> > > > This however doesn't change the fact that most authors define a
> > > > (mathematical) relation as a set of ordered tuples, which means a
> > > > function is not a relation (assuming, as most do, that a function has
> > > > a defined domain and codomain).
>
> > > I don't understand how the conclusion follow from the premise.
>
> > I am afraid that you don't understand above conclusion because you
> > don't understand what function is.
>
> What makes you think that?

Definition1 A function from A to B is a rule that assigns, to each member of set A, exactly one member of set B.

Is this good or bad definition for a function? If you thing that this is good definition for a function then please explain why this is good definition, else please explain why it is not good definition.