Re: Question about Date & Darwen <OR> operator

VC wrote:
> Can anyone give at least an informal definition of what <OR> and <AND> are
> since the formal one (as quoted ) appear rather nonsensical ? Without such
> definition any discussion is nonsensical too.

Informal definition is rather easy.

Let x be domain of values {a_1, a_2, ...} y be domain of values {b_1, b_2, ...}
z be domain of values {c_1, c_2, ...}

Consider the cartesian product space
P={a_1, a_2, ...}x{b_1, b_2, ...}x{c_1, c_2, ...}

Then, relations R_1(x,y) and R_1(y,z) both are cylindric sets in P. (Cylindric sets are geometric objects which are invariant under projection). R_1(x,y) <AND> R_1(y,z) is the formal intersection of the cylindric sets, and R_1(x,y) <OR> R_1(y,z) is their union. Received on Wed Sep 07 2005 - 00:55:56 CEST