Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

Marshall Spight wrote:
> I've never seen
> a definition of RT that mentions programs; it's always been about
> the return values of a function. I realize that one may consider
> a function to be a program, but I believe in this case the distinction
> is useful.

The informal RT definitions (that we used) talk about *the result* (not just the return value) which would be for, say, the 'print' function a pair of <return_value, state_of_the_world>. The next run would produce <the_same_return_value, another_state_of_the_world>. Interestingly, the next run may produce <a_different_return_value, the_same_state_of_the_world> if the printer is broken ! So, you see, even if we abandon the notion of state (a wrong decision, of course) and use your narrow definition (just the return value), the function might still produce different results that depend not only upon the arguments but also on the outside world behaviour.

Incidentally, in functional program, the entire program is nothing more but a function definition (not surprisingly) which includes (or not) other function definitions that comprise/compose the whole program(main function).

vc Received on Mon Jun 27 2005 - 20:41:38 CEST