Re: pro- foreign key propaganda?

From: David Cressey <>
Date: Tue, 20 May 2008 10:21:56 GMT
Message-ID: <8DxYj.2918$pk1.637_at_trndny07>

"paul c" <toledobysea_at_ac.ooyah> wrote in message news:o1nYj.152086$Cj7.54265_at_pd7urf2no...
> David Cressey wrote:
> ...
> > Well, as you've said more than once, the concept of primary key doesn't
> > exist at the RDM level of abstraction. ...
> Maybe not "primary key" but the idea of a key is certainly inherent in
> the RDM assuming you will admit 'rename' plus the original operators
> natural join, select and project, to it.

Absolutely. In the previous comments in this thread, the term "candidate key" was used.
You can shorten that to simply, "key", if you like. No problem. The word "candidate" was introduced into the terminology with the idea that the primary key would be selected among the candidate keys. What I think I've learned in c.d.t. in years gone by is that the selection of one candidate key to be the primary key is not inherent in Relational modeling. IIRC, I learned it from Bob's writings.

> (Heh, the first time I saw that "aref" tag in HTML, I thought "good for
> them, they've lifted a useful idea of Codd's from twenty years ago and
> generalized it to a mere reference"! Then I realized there was no "aref
> constraint", so the author doesn't have an inherent way to make the html
> stick. The bind is so late that only the user knows - weird!)

I don't know "aref". That's a new one on me.

But don't get me started on HTML. I think that it was a wonderful thing for a physicist to come up with a way of propagating information over the internet without being blocked by format incompatibilities. But I also think that HTML was the ultimate perpetration of an uncontrolled graph of "hrefs" and pages. It has all the problems of a graph DBMS, and then some. Received on Tue May 20 2008 - 12:21:56 CEST

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