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@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

Received on Mon Mar 07 2005 - 16:16:51 CST

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