Re: BCNF: superkey or candidate key ?

From: Jan Hidders <hidders_at_gmail.com>
Date: 25 Sep 2006 02:09:30 -0700
Message-ID: <1159175370.783323.316310_at_e3g2000cwe.googlegroups.com>


masong_at_sbcglobal.net wrote:
> "Database In Depth", C.J. Date, May 2005, p.140:
> Relvar R is in BCNF if and only if, for every nontrivial FD A -> B satisfied
> by R, A is a superkey for R.
>
> "Database Modeling and Design", 4th Ed., Torey/Lightstone/Nadeau, Sep 2005,
> p.115:
> A table R is in Boyce-Codd normal form (BCNF) if for every nontrivial FD X
> -> A, X is a superkey.
>
> "Fundamentals of Database Systems", 5th Ed., Elmasri/Navathe, May 2006,
> p.368:
> A relation schema R is in BCNF if whenever a nontrivial functional
> dependency X -> A holds in R, then X is a superkey of R.

Of course, those are the standard definitions, but you claimed that you had seen one that said:

"Previously he (and others) defined it where A had to be a candidate key
(which is irreducible)."

So a definition like: A relation schema R is in BCNF if whenever a nontrivial functional
dependency A -> X holds in R, then A is a candidate key of R.

That would not be equivalent to the standard definitions, so I wondered where you had seen such a definition.

  • Jan Hidders
Received on Mon Sep 25 2006 - 11:09:30 CEST

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