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Re: Artificial Primary keys

From: Jan Emil Larsen <jel_at_g-it.dk>
Date: Fri, 25 Jan 2002 17:25:13 +0100
Message-ID: <3c5186c2$0$14015$edfadb0f@dspool01.news.tele.dk>

"Bernard Peek" <bap_at_shrdlu.com> skrev i en meddelelse news:ZNUXYIl4cVU8Ew7o_at_shrdlu.com...
> In message <3c505454$0$89112$edfadb0f_at_dspool01.news.tele.dk>, Jan Emil
> Larsen <jel_at_g-it.dk> writes
> >
> >"Bernard Peek" <bap_at_shrdlu.com> skrev i en meddelelse
> >news:1RWc$oFw4BU8Ew$$@shrdlu.com...
> >> In message <3c4f3e5e$0$13976$edfadb0f_at_dspool01.news.tele.dk>, Jan Emil
> >> Larsen <jel_at_g-it.dk> writes
> >>
> >> >A key should be imutable, and should therefore be without information
in
> >it
> >> >self.
> >>
> >> The first is true but the second doesn't follow from it.
> >
> >That is right. It goes the other way round: If it has information in it
self,
> >it may change.
> >No-information in the key is a measure to secure immutability.
>
> No, that's still not right. Immutability is important but artificial
> keys are not the only way to get it. If you have a natural key that
> truly identifies one and only one thing then it is immutable. If it
> changes then either it wasn't a real key or someone recorded the wrong
> value.

Yes, it IS right :-)
If the key holds information, the key will (must) change if that information changes.
If the key do not hold information, then nothing force it to change.

Identifying one and only on thing isn't enough to keep the key immutable. "Things" may change, eg. Name or even SSN, but they identify at any time only one "thing".

Or could you give an example - that is: of a natural key that holds information, but is immutable? Received on Fri Jan 25 2002 - 10:25:13 CST

Original text of this message

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