Re: Relational lattice

From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Tue, 15 Mar 2005 19:52:03 GMT
Message-ID: <D1HZd.38493$ue7.3246150@phobos.telenet-ops.be>

Vadim Tropashko wrote:

> Vadim Tropashko wrote:
> 

>>How about small counter example?

Oh, that would be splendid. :-)

>>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).

Hmm, your relation doesn't satisfy the second part of condition 2 because X12 <> R.

• Jan Hidders

Received on Tue Mar 15 2005 - 13:52:03 CST