# Re: BCNF: superkey or candidate key ?

From: Jan Hidders <hidders_at_gmail.com>

Date: 21 Sep 2006 08:24:08 -0700

Message-ID: <1158852248.305329.131550_at_h48g2000cwc.googlegroups.com>

Date: 21 Sep 2006 08:24:08 -0700

Message-ID: <1158852248.305329.131550_at_h48g2000cwc.googlegroups.com>

masong_at_sbcglobal.net wrote:

> C.J. Date in a recent text defines BCNF in terms of superkey.

*> ... every nontrivial FD A -> B satisfied by R, A is a superkey for R.
**>
**> Previously he (and others) defined it where A had to be a candidate key
**> (which is irreducible).
*

Really? Could you give a reference where Date (or someone else) wrote that? Sometimes you will find definitions that say something like "if every non-trivial left-irreducible FD has a candidate key as its determinant" but I've never seen it without the "left-irreducible" requirement (or the assumption that your set if FDs is irreducible) and that would in fact be incorrect.

So as far as I know the defintions have remained equivalent.

- Jan Hidders