Re: Relational Lattice, what is it good for?

Marshall Spight wrote:
> One goes from 3 to 4 by applying the definition of the inner union.
> The two operands are both projected over the intersection of their
> attributes. Because there are seven categories of attributes,
> (depending on which relation(s) they are in) the notation is
> laborious. But it is the simplest one I could think of.

Let see. We start with 3:

(A && B) || (A && C) = { (a,ab,ac,abc,b,bc) |

       (a,ab,ac,abc) in A and (ab,b,bc,abc) in B }  ||

                                      { (a,ab,ac,abc,c,bc) |
                              (a,ab,ac,abc) in A and (c,ac,bc,abc) in C

Formally aplying the inner union definition we have

{(a,ab,ac,abc,bc) | (a,ab,ac,abc,bc) in { (a,ab,ac,abc,b,bc) |
       (a,ab,ac,abc) in A and (ab,b,bc,abc) in B }
or  (a,ab,ac,abc,bc) in { (a,ab,ac,abc,c,bc) |
                              (a,ab,ac,abc) in A and (c,ac,bc,abc) in C

Now I'm lost. How do we simplify the doble nesting of sets? Received on Sat Feb 18 2006 - 19:32:30 CET