Re: "Armstrong's axioms" augmentation - help plz
From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Mon, 07 Mar 2005 22:16:51 GMT
Message-ID: <np4Xd.32216$ub7.3221532_at_phobos.telenet-ops.be>
Date: Mon, 07 Mar 2005 22:16:51 GMT
Message-ID: <np4Xd.32216$ub7.3221532_at_phobos.telenet-ops.be>
love boat via DBMonster.com wrote:
> I understand the Augmentation rule:
> { X -> Y } |= XZ -> YZ
>
> but I don't understand why the rule can also be stated as:
>
> { X -> Y } |= XZ -> Y
>
> Why is this?
It cannot. If you replace the first rule with the second you will not derive all FDs that hold.
- Jan Hidders