Re: Principle of Orthogonal Design(B

On Feb 7, 1:54 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> "JOG" <j..._at_cs.nott.ac.uk> wrote in message
>
> news:c8bd75c2-5a4b-4456-8646-4ed912cc578b_at_i29g2000prf.googlegroups.com...
>
> > On Feb 7, 11:21 am, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> >> [snip]
> >> A join is not a constraint, is it?
>
> > Now that's a very interesting question. Let me be polemic and say I
> > think it is.
>
> Interesting indeed. So, for example, the join of relations
>
> P {A, B, C} and
> Q{D, E, F, G}
>
> yields a relation with the heading,
>
> {A, B, C, D, E, F, G}.
>
> Can you explain what is constrained by P JOIN Q?

The resulting set of tuples, lets call it R is. So again, your example in set builder notation:
R = { {A:a,...,G:g) | (A:a,B:b,C:c) $B":(B P $B"J(B (D:d,E:e,F:f,G:g) $B":(B Q }

Here we're constraining a possibly infinite set of tuples, just as if we were constraining a set of numbers, S, to come from the naturals and to be less than ten we'd have:
S = { x | x $B":(B P $B"J(B x < 10 }

Course, I guess the perspective I'm throwing about above wouldn't make any sense to proponents of there being a separate "header" entity, which I think is D&D's line (as opposed to Pascal's say). Any thoughts? Received on Thu Feb 07 2008 - 16:47:11 CET