# Re: BCNF: superkey or candidate key ?

From: Bob Badour <bbadour_at_pei.sympatico.ca>

Date: Mon, 25 Sep 2006 11:26:42 GMT

Message-ID: <S1PRg.38577$9u.330670_at_ursa-nb00s0.nbnet.nb.ca>

> Of course, those are the standard definitions, but you claimed that you

Date: Mon, 25 Sep 2006 11:26:42 GMT

Message-ID: <S1PRg.38577$9u.330670_at_ursa-nb00s0.nbnet.nb.ca>

Jan Hidders wrote:

> 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.*If A is a candidate key, then a functional dependency of the form B -> X would hold where B is any superkey of A. Would it not? Received on Mon Sep 25 2006 - 13:26:42 CEST