Re: What to call this operator?

"Marshall Spight" <marshall.spight_at_gmail.com> wrote in message news:1119842835.425835.266500_at_f14g2000cwb.googlegroups.com...
> In chapter 4 or The Third Manifesto, D&D define a "new relational
> algebra."
> This algebra includes two operations named "<AND>" and "<OR>". (They
> use some weird triangle characters which I'm approximating with <>.)
>
> Given relations S and T, having sets of attributes a (only in S),
> b (in both S and T) and c (only in T), they define:
>
> <AND> as { (a, b, c) | (a, b) in S, (b, c) in T }
>
> <OR> as { (a, b, c) | (a, b) in S, c unconstrained UNION
> (a, b, c) | (b, c) in T, a unconstrained }
>
> "unconstrained" means that all values from the domain are present.
>
> They go on to point out that <AND> is the natural join, but they
> don't give a name to <OR>.
>
> Does anyone have a good idea for what it should be called?
> I don't like "or" because it's ambiguous with the boolean
> operator. "<OR>" isn't great for syntactic reasons. "Disjunction"
> is cumbersome. I'd like to hear something analogous to "join."
> What about "meet", does that work? It's the usual counterpart to
> "join" but I don't know enough math to decide if it's appropriate.
>
> Anyone have any other ideas?
>
>
> Marshall
>

With apologies to Humberto Eco, you could call it a "rose".

But seriously, I'm unable to figure out from the formal description what it is. more importantly, I'm unable to figure out what it is FOR. Not that there's anything wrong with your formal description. It's just my own unfamiliarity with it that causes problems.

How does <OR> differ from "full outer join"?

Is the "unconstrained" construct just another way of introducing NULLs (for unknown values), without using that dreaded term?

What is the value of <OR> MINUS <AND> ???

What would <OR> be useful for?

Sorry to answer a question with so many questions, but it's the best I can do, for now. Received on Mon Jun 27 2005 - 18:01:44 CEST