Re: ?? Functional Dependency Question ??

From: Walter Mitty <>
Date: Sat, 18 Oct 2008 13:06:30 GMT
Message-ID: <qblKk.1902$>

<> wrote in message
> Hi all,
> I'm reading Elmasri & Navathe's "Fundamentals of Database Systems, 4th
> ed.". The authors discuss how, given a set if FDs, additional FDs can
> be inferred. The authors provide six "Inference Rules". At one point
> the authors say this:
> "Although X->A and X->B implies X->AB by the union rule stated above,
> X->A, and Y->B does *not* imply that XY->AB."
> I'm not seeing this. It seems to me that X->A, and Y->B *DOES* imply
> that XY->AB.
> I'm sure I'm wrong but I'm not seeing it. Can someone explain?
> Thanks

If I understand it right, XY does not imply X and Y. Received on Sat Oct 18 2008 - 15:06:30 CEST

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