Re: No exceptions?

Bob Badour wrote:
> Jon Heggland wrote:

>> I don't think the confusion is on my part. "Key" (as opposed to
>> "superkey") already implies irreducibility; that's the point of the
>> superkey/key distinction. A "candidate key" is certainly irreducible
>> (due to being a key), but "irreducible key" is redundant.

You are mistaken.

> A definition is like a contract for communication and understanding.
> When you arbitrarily redefine key to mean candidate key, you breech that
> contract and the result of that breech is confusion.

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?

> By redefining key to mean candidate key, one loses the term that means
> key. By redefining superkey to mean proper superkey, one loses the term
> that means superkey.

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.

> Your laziness about typing the full names causes confusion and
> interferes with communication.

Your laziness about providing substantial arguments in favour of your position in this kind of tedious discussion prolongs it unnecessarily.

-- 
Jon