Re: No exceptions?

> > Candidate key, superkey and proper superkey all have different precise
> > meanings and all of them are keys.
>
> You are mistaken.

He's not mistaken in the eyes of all those who believe one should abide by the definitions given by the original inventor of the model. Of all current relational writers, Date is the one who is closest to being that "authentic source". Admittedly, his ideas are no longer exactly the same as what Codd's ideas were in the seventies (e.g. he dropped the notion of "primary key"). But I regard the fact that the ideas have evolved as a good thing rather than a bad one.

> I keep five database textbooks in my office: Date, Elmasri/Navathe,
> Garcia-Molina/Ullman/Widom, Ramakrishnan/Gehrke, and Riccardi. All of
> them agree with me: a key is an irreducible superkey. Granted, two of
> them say that "key" is short for "candidate key", but that does not
> invalidate my position; one says that "candidate key" is what you call a
> key when a relation has more than one; and the others don't use the term
> at all, afaict. All agree that a proper superkey is not a key.
>
> Whose "contract" should I abide by? Yours, or theirs?

Check out Date. I believe you'll find Bob's statements are in line with Date's. And Date is the one who is closest to being the "authentic source" for the relational model.

> Please back up your statements that I am redefining anything. The terms
> "key", "superkey" and "proper superkey" are sufficient. The term
> "candidate key" is obviously disputed, and it is unnecessary as well.

If one agrees to abide by Date's definitions, then I believe your statements indeed constitute redefinition. If you don't agree to go by Date's definitions, then don't argue with anyone who does. Received on Mon Jul 03 2006 - 12:14:08 CEST