Re: What to call this operator?

Mikito Harakiri wrote:
> "subset of" is generalized to be applicable to any pair of
> database relations.

There are couple minor but cute comments about the "is subset of" relation.

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. Received on Thu Jun 30 2005 - 18:53:50 CEST