"David Cressey" wrote in message
news:%9lnj.5893$cm6.4751@trndny05...

When it is managed by other people, it is subject to mismanagement.
Changing values that ought to be immutable is one of many ways that
natural
keys can be mismanaged.

As I said before, I prefer to use natural keys where ever possible. If
that's not possible due to mismanagement of the natural keys, I'll use
synthetic keys.

I think you may be asking too much of a natural key. I always took "stable"
to mean *almost* never changes ratherer than meaning absolutely immutable
(which I take to mean "intrinsically incapable of changing"). But whatever
one thinks it should mean, one always has to accommodate the possibility
that a key value will be mis-typed during manual entry by a user, and
therefore that it will have to be corrected. Mismanagement is, as you
rightly say, a fact of life.

But that's not usually a sufficiently good reason to introduce a synthetic
key. I have found it possible to tolerate quite a lot of updates to
supposedly stable keys using ON UPDATE CASCADE, with imperceptible
response-time costs. (One can of course measure the costs, but that's not
what counts.) A key would have to be really unstable to justify using a
synthetic key IMO.

Roy