Re: Thinking about MINUS

J M Davitt wrote:
[...]
> All this "boolean operations on sets" has me scratching my head. There
> is, underneath it all, the presumption that one really means "is an
> element of," right?

Yes, I think so

> I mean, what could the meaning of "NOT (strawberry
> OR apple) AND grape" be?
>

NOT is analog to COMPLEMENT, and I think it should be:

NOT ( {strawberry} OR {apple} ) AND {grape} => COMPLEMENT ( {strawberry} UNION {apple} ) INTERSECT {grape} => { x1, ..., xn, grape} INTERSECT {grape} => {grape}

[...]

>
> Sure, we can think of JOIN as an analog to AND and UNION as an analog to
> OR, but they are very different operations.
>

Both structures discussed are boolean algebras, so they are indeed very analog. I prefer to think of AND as INTERSECT, but perhaps it is possible to use JOIN instead. Another well known boolean algebra is Z2 under addition and multiplication.

/Lennart

[...] Received on Sun Jan 07 2007 - 17:18:28 CET