On Sun, 2015-01-25 at 14:09 +0100, Alban Hertroys wrote:
> >> The theory got me intrigued. google
> >> (http://en.wikipedia.org/wiki/Codd%27s_12_rules) says:
> >> rule 3: "systematic treatment of null values"; hmmm.... this is a little
> >> broader then "support for null". I would think, that:
> >> 1. if a sequence of "update XX set fk_field=null; then delete YY depending
> >> on that FK", for a particular schema definition works ...
> >> 2. so the implementation of FK should support that too ... to be called
> >> "systematic", right?
> >> 3. and the simplest way to do that for the case at hand, within an "on
> >> delete action", is to skip those parts of FK, that are marked as "not
> >> null" within the referring table. That would be a "requirement" for rdbms
> >> implementation that claims compliance with Codd rule nr.3 :)
> >
> > I translated Codd-relationality to English, possibly it’s named differently.
> >
> > Oddly enough, I can’t find any reference to Codd being responsible for this
> > rule anywhere on the internet. What I did find is that the theory I
> > referred to stems from 1970(!), but that’s the closest I got.
>
> My teachers got back to me; a while ago already, to be fair. They were as
> surprised that this can't be found on the internet as I was, but it should be
> possible to find it in printed form. I'd suggest a university library or a
> good technical book store.
>
> Apparently, this particular theory is explained in E.F. Codd: "The relational
> model for database management". There are probably other books that do too.
>
> Unfortunately, I do not own a copy so I can't verify. If anyone who does own
> a copy could confirm or even quote the relevant section, that would be great.
> Better yet, perhaps this should find it's way (back) to the internet? I'm
> still much surprised that Wikipedia didn't have this.
>
> Oh, and perhaps we could get a reference in the PG docs on primary keys and
> NULLs to the theory? Do we have such things in the docs? It sounds like a
> good idea to me, I always find it helpful to know why things are how they
> are. But I don't write the docs so this is just one for the ideas-box.
>
> Cheers,
>
> Alban Hertroys
> --
> If you can't see the forest for the trees,
> cut the trees and you'll find there is no forest.
>
>
>
The following link
http://www.databaseanswers.org/codds_rules.htm
sets out Ted Codd's rules according to C.J. Date.
I don't have a copy of the book so I can't verify the accuracy of what
is published at this link.
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