Re: Relational Lattice, what is it good for?

Marshall Spight wrote:
> > Alternatively, you have to use existential qualifier, as Jon written in
> > the old exchange.
>
> I only vaguely recall this exchange, and I seem to remember that
> I didn't understand it at the time.

A(x,y) || B(y,z) = { y | exists x A(x,y) or exists z B(y,z) }

> > This step [4-5] is not obvious. Again, careful manipulation would involve
> > projection.
>
> I don't understand the problem. This step relies only on the
> distributivity of the boolean algebra; note that the operands of the
> boolean operators ("and", "or") in the expressions are syntactically
> unchanged between steps 4 and 5. I assumed I could rely on
> boolean distributivity; was that an unjustified assumption?

Oops, I'm sorry I meant 3->4. Received on Sat Feb 18 2006 - 10:42:59 CST