Re: Question about Date & Darwen <OR> operator

Marshall Spight wrote:
> Mikito Harakiri wrote:
> > Assuming domains x in {1,2} and y in {a,b} what is the result of
> >
> > {(x=1)} <OR> {(y=a)}
>
> As I understand it, the result would be:
>
> x y
> ---
> 1 a
> 1 b
> 2 a
>
>
> which is
> { (x, y) | x = 1 or y = a }

>From http://c2.com/cgi/wiki?RelationalAlgebra

a OR b : An extended form of union; if the headings of the operands differ, then "missing" attributes take on all possible values. Thus the result may be very large or even infinite. When the operands have the same heading, then this is the same as a traditional SQL UNION, except that all duplicates are always removed.

This informal description matches the other alternative. What is the formal definition? Received on Sat Sep 03 2005 - 01:18:17 CEST