Re: constraints in algebra instead of calculus

On Jun 18, 5:48 pm, paul c <toledobythe..._at_oohay.ac> wrote:
> These are the ways I can think of to express the constraint:
>
> 1. COUNT(R{A}) = COUNT(R)
> 2. ( R <AND> (R RENAME A as a, B as b) ) WHERE A = a & B != b IS EMPTY
> (using a grab-bag syntax, possibly inviting correction umpteen + 3)
> 3. the elaborate one using GROUP that Jon H corrected
> 4. something like R GROUP {ALL BUT} as c <AND> constraint{c} IS TRUE/NOT
> EMPTY (where constraint has one tuple for each legal R value and c is
> an rva)

5.

R <AND> (R RENAME B as B') )
IS
R WHERE B = B' where the "IS" symbol is relational equality. Relational equality (aka "IS") provides a succinct way to say that the symmetric difference of the relations

R <AND> (R RENAME B as B') )

and

R WHERE B = B' is empty. Received on Mon Jun 18 2007 - 20:23:26 CDT