Martin:

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I read here also that state abbreviation makes a good natural key
because it isn't expected to change. FALSE! As you know, USA is
not the only place where people use bussiness apps, and this is a
total lack of vision. Different countrys have different codign
standard for cities, counties, and such, and in many of them those
change from time to time -somewhere even monthly 8-).

Being in a global market (in southamerica is better for you to try
to reach other countries because one's own is ussually a small market
or at many times a though one), we qucickly discovered that natural
keys doesn't endure very much.
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A total lack of vision??? You seem to be the one making the assumption that all applications must handle address data from foreign country. Some applications by their nature can only be used in the locale it was written for because the context is not, has not, and very likely will never exist for any other locale. Preparing for all possibilities is nice but it is certainly not always practical.

By the way, I generally agree with Walter on the natural key issue except that I don’t use composite keys for my own personal reasons. I have been doing this stuff for over 10 years and none of the natural key selections I have made have have suffered any data change...

Daniel