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 - 06:26:42 CDT
