Re: A real world example

Bob Badour wrote:
> anithsen_at_gmail.com wrote:
>
> > "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> > news:MNCDg.8096$9T3.560_at_newssvr25.news.prodigy.net...
> >
> >>"Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> >>news:fqmDg.39802$pu3.533163_at_ursa-nb00s0.nbnet.nb.ca...
> >>
> >>[snip]
> >>
> >>
> >>>A natural key is simply a familiar surrogate. Nothing more. Nothing less.
> >>
> >>I disagree. A the value of a surrogate (at least according to Codd, and
> >>also Date, if I recall correctly) should permanently identify something.
>
> Cite? The value of a candidate key is it permanently identifies
> something; hence, the importance of stability as a design criterion.
> That is as true for natural keys as for surrogates.
>
>
> > The only way one can have an attribute whose values never change is by
> > violating information principle.
>
> How so? I agree that hiding an attribute violates the information
> principle, but I don't see how precluding changes does.
>

Ah.. data independence, not information principle. My bad.

I was thinking of the facilities in some SQL products like version timestamps, row ids etc. used as column values, but non-updateable purely due to its dependence to the physical model.

[snipped]

--
Anith