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 <>.)

on pg 44 they call those characters arrowheads. i like the association with anthropology.

>
> 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>.

in the 'parallel' paragraphs on pg 56 they call it 'union'. they also suggest 'conjoin' and 'disjoin'.
>
> 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.

this field is full of people calling different things by the same names.

   personally, i'm not bothered by 'and' and 'or' or 'relational and', 'relational or'. it's all a force-fit anyway, trying to obtain a single relation result.

>
> Anyone have any other ideas?

multiple relation results!

p Received on Mon Jun 27 2005 - 15:18:25 CEST