Re: RL notation

On Feb 7, 1:10 pm, Marshall <marshall.spi..._at_gmail.com> wrote:
> I'm not even absolutely sure there are two different
> equalities, though. Maybe there is just the one equality,
> and we define the relational comparison with it. Vice versa
> also works. But we need *something* besides just the
> two lattice operators or we can't compare relations.

I'm not so concerned about syntactic sugar as conceptual flaws. Can we have just one more constant: Universal Equality Relation (denoted as E)? Then x=y is defined E projected to attributes x and y. What abouy incompatible domains, though? If x and z are incompatible, we can't define E projected to x,z as empty. We have to (somewhat counter intuitively) to define x=z as a cartesian product of the domains!

So we have 5 constants: 00, 01, 10, 11 and E -- sounds too many. Although, 10 and 01 are the least intersting elements of RL, so it is really only 00, 11 and E that matter.

> Yes, there is some concern about relation variables
> and attribute names appearing at the same lexical
> level in expressions, but my tendency is to believe the
> brevity is worth the risk...

Again, syntactic sugar doesn't bother me much. I'd suggest operating RL expressions in completely attribute free fascion. Whenever there is an expression and there is a relation with some specific constraints (e.g. having attribute x, or being empty), then it could be rewritten in more general way without these constraints. In principle generality should lead to simplicity.... Received on Thu Feb 07 2008 - 23:04:24 CET