Re: Question about Date & Darwen <OR> operator

VC wrote:
> "Marshall Spight" <marshall.spight_at_gmail.com> wrote in message
> >
> > I would propose something like
> >
> > Given
> > A:(a:Ta,ab:Tab)
> > B:(b:Tb,ab:Tab)
>
> I am not sure I understand the notation. Could you clarify what '(a:Ta,
> ab:Tab)' is ?

I try to use the 'x:T' form exclusively to mean 'x has type T.' Above I'm trying to say, "A has the type: set of (set of attributes a with type(s) Ta, and set of attributes ab with types Tab.)"

Ordinarily I wouldn't find it necessary to bring the types in, but in this case we need to name Ta and Tb specifically because <OR> has us doing a cross product with the entire set of values of the type.

> > A <OR> B = { (a,ab,b) |
> > ((a,ab) in A cross product Tb)
> > union
> > ((b,ab) in B cross product Ta)
> > }
>
> Regardless of what Ta, Tb stand for, I object to the (a, aab) notation
> which denotes an ordered pair. Since a tuple is a set of (A,T,v) triples,
> should not it be {a, ab} ?

The more I think about it, the more I agree that it should be {}.

Marshall Received on Sun Sep 04 2005 - 16:30:05 CEST