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Home -> Community -> Usenet -> comp.databases.theory -> Re: Artificial Primary keys

Re: Artificial Primary keys

From: Jan Emil Larsen <jel_at_g-it.dk>
Date: Mon, 28 Jan 2002 14:35:01 +0100
Message-ID: <a33k29$16uu$1@news.net.uni-c.dk>


Forgot one thing:

"Bernard Peek" <bap_at_shrdlu.com> skrev i en meddelelse news:V4YEVzEOOIV8Ewhm_at_shrdlu.com...

> >Or could you give an example - that is: of a natural key that holds
> >information, but is immutable?
>
> I quoted one a few days ago, a natural key that uniquely identifies a
> person. If you have the precise location and time that someone is born
> you can uniquely identify them. Once they have been born the data is
> immutable.

By using such a key we agree that this key will contain information. I was saying that a key should not carry information, as it then would not be immutable.
We agree that it should be immutable. You think that it is immutable because "it is a natural key, that identifies one and only one thing", and does could not mutate.

In theory, your "time and place of birth"-key is indeed immutable and identifying - or almost so: by the laws of physics you adhere to, you must give a frame of reference to specify time and place in coordinates (as you can only represent simple attributes). In principle the frame of reference could be changed, eg. by a geodesic new measurement or change of conventions. This is purely speculation, but I assume your example is too.

I practice, if "time and place" by an error was recorded wrongly, you would have to change the key - not because then person became another person, but due to an error. Errors happens.

By using a surrogate key you would NEWER end in such a situation. And why is that: because it is a key that carries NO information, and thus NEVER has to be changed. Received on Mon Jan 28 2002 - 07:35:01 CST

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