Re: dumb terminology question: candidate key

Jonathan Leffler wrote:
> Marshall Spight wrote:
> > Does anyone have any insight or information on the origin
> > of the term "candidate key"?
>
> In the bad old days - say 1990 - the perceived rules of the RM were that
> every relation had one primary key. Unfortunately, some relations had a
> number of unique keys - think of a table of chemical elements, where
> atomic number, symbol and name are each possible keys (that is,
> candidate keys) - so if you selected one key as the primary key (which
> one), the others were alternative (or was it alternate) keys. There was
> also the entity integrity rule that said that primary keys could not
> allow nulls - but alternative keys could (but an alternative key that
> allowed nulls was no longer a candidate key and hence not really an
> alternative key after all; what a tangled web nulls weave!) The
> collection of unique keys were all candidate keys - one was selected as
> the primary, and the rest became alternatives.

I see. So the thing it's a candidate for is being the primary key.

Wow.

> Then the primacy of primary keys was called into question; normalization
> theory didn't deal with primary keys, only with candidate keys. So
> primary keys lost some of their significance, and the term that was left
> was candidate keys.

Now that we know better, I propose that we drop the term "candidate" from "candidate key" and leave just "key." I say this with all the naive optimism of youth. (A good trick at my age.)

Marshall Received on Fri Jul 15 2005 - 09:57:11 CEST