Re: Constraints and Functional Dependencies

On 24 fév, 21:41, paul c <toledobythe..._at_oohay.ac> wrote:

> I don't know where to look for Cimode's proof but I think what Marshall
> defined is what I call a "reference", which seems more general than
> Codd's original foreign key, ie., doesn't exclude the possibility of the
> reference being a key in the referenced table, if the person who
> declares the reference so desires. I take it that you want to read
> "foreign key" literally and insist that the reference involve a key
> defined for example, the way Marshall defined a key. If I read you
> right, that's okay by me but I think "reference" encompasses "foreign
> key" in a way that never diminishes any table a designer who wants to be
> literal declares at the same as it allows the rest of the table definers
> much more leeway.
I am sorry you can't see it as masterdam does. See alternate formal proposition may help clarify.

You *may* be right on the reference matter. Nevertheless, don't you think that something is missing?

> The term "key" is a bastard in the first place. It seems to have been
> inherited from the times when hardware recognized keys by their physical
> position.
I have always asked myself such question. The context explanation of key is a plausible one. My guess, Codd had to assume at some extent a concept that could embody domain intersect in a coherent manner so that it could be understood better by 70's computing community.

[Snipped] Received on Sun Feb 25 2007 - 12:34:13 CET