# Re: BCNF: superkey or candidate key ?

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)."

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

- Jan Hidders