Re: "Armstrong's axioms" augmentation - help plz
From: paul c <toledobythesea_at_oohay.moc>
Date: Tue, 08 Mar 2005 03:41:07 GMT
Message-ID: <n99Xd.599930$Xk.252349_at_pd7tw3no>
>
>
> It cannot. If you replace the first rule with the second you will not
> derive all FDs that hold.
>
> -- Jan Hidders
Date: Tue, 08 Mar 2005 03:41:07 GMT
Message-ID: <n99Xd.599930$Xk.252349_at_pd7tw3no>
Jan Hidders wrote:
> 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
The first 'rule' is X -> Y, and so is the second! What's the difference?
p Received on Tue Mar 08 2005 - 04:41:07 CET