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Home -> Community -> Usenet -> comp.databases.theory -> Re: Relational lattice
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