# Re: what are keys and surrogates?

Date: Mon, 14 Jan 2008 09:39:58 -0800 (PST)

Message-ID: <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

*>
**> news:b05f3396-4c1f-4710-8d27-d4940b7e689f_at_e10g2000prf.googlegroups.com...
**>
**> > 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. As the function is basic thing in mathematics and computer science, let me give you the simplified schema for a function, so that you can get an intuitive picture about the function:

|-------------| --- x ---- >| f-maschine | ------ f(x) ----- > |-------------|

Where x is input in the "f-machine" and f(x) is output. Received on Mon Jan 14 2008 - 18:39:58 CET