>George:
>
>> Natural keys, anyone?
>
>Yes.
>(1) A DOT code is a 9-digit string identifying the occupation. The first few digits are significant to identify the categories.
>(2) The 2-letter postal abbreviation for state can be used as PK for a USState table. It carries some meaning because you can print this abbreviation to identify the state on a letter and the USPS knows what its signification.
>
>Many lookup tables can use natural keys as PKs if the natural key values are almost set in stone.
>
Daniel,

They'd better be, otherwise...As Jim Booth and Steve Sawyer pointed out in their "Effective Techniques..." book, not everything that we assume to be guaranteed to be unique are. The example they used is Social Security Numbers. There have been instances of duplicates among living persons.