Re: What to call this operator?

Marshall Spight wrote:
> 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?

The outer union operator dates back to Codd "Extending Relational Model to capture more meaning"

See also Galindo-Legaria "Outer joins as disjunctions"

In my opinion this definition of union is less interesting than http://arxiv.org/pdf/cs.DB/0501053 Received on Mon Jun 27 2005 - 18:43:41 CEST