Re: Relational lattice

From: Vadim Tropashko <vadimtro_invalid_at_yahoo.com>
Date: 14 Mar 2005 16:10:35 -0800
Message-ID: <1110845435.238466.181810@z14g2000cwz.googlegroups.com>

Vadim Tropashko wrote:
> How about small counter example?
>
> Consider
>
> R=
>
> x y
> - -
> 1 2
> 2 2
> 2 3
> 3 3
>
> I suggest that
>
> X = X12 join X34 join X56

"join" here is merely a Cartesian Product. (ASCII constraint: Can't use "x" for the product as it can be confused with the variable. "*" sign for the cartesian product is goofy.)

> where
>
> X12=
>
> x y
> - -

typo:

x1 x2
-- --

> 1 2
> 2 2
> 2 3
> 3 3
> 3 2
>
> X34=
>
> x y
> - -

typo:

x3 x4
-- --

> 1 2
> 2 2
> 2 3
> 3 3
> 3 2
> 1 3
>
> X56=
>
> x y
> - -

typo:

x5 x6
-- --

> 1 3
>
> is a solution that meets conditions 1-4. (The fact that x5=1 and x6=3
> is the only pair is especially handy when checking the above
> conditions).
Received on Mon Mar 14 2005 - 18:10:35 CST