Re: What to call this operator?

Vadim Tropashko wrote:
> Let use capital letters for (database) relation variables. Normally we
> write A(x,y) to denote a relation A with attributes x and y. For empty
> relations A(x), A(y), B(z) let just write them as x,y,z. Let also "<="
> to denote "is subset of". Then
>
> x|><|y <= A(x,y)
>
> or more succinctly
>
> x|><|y <= A
>
> Similar to math nothation let's drop the join symbol, assuming that in
> the absence of the other operators it's implicit between any 2 relation
> variables. There we have
>
> x y <= A
>
> That's right, instead of bracket notation A(x,y) saying that relation A
> has attributes x and y, we can just write "A >= x y" implying that A is
> a superset of join of empty relations x and y.

On a symmetrical note, lets use capital letters X, Y etc to denote an infinite relation each of which is a full domain. Then

A <= X Y Received on Thu Jun 30 2005 - 21:02:09 CEST