> here (I believe Barbara Paltiel was one) have said that primary keys should > only be used for their uniqueness, and should be generated by > incrementation or random methods. I didn't understand their reasons, and I > didn't want to ASSUME, though I'm free to SUPPOSE, that I'm smarter than > everybody else. I thought the general idea was that generated key is used when no natural primary key appears... but maybe that's just my personal default. Besides, defaults may be obvious in some cases, but when we talk design, there are no defaults - we must define them first. In your case, this came out as a natural primary key, so inventing a generated one would, IMO, be superfluous. Now when I saw the logic of your natural keys, I remember I've been doing things like that - for example, a walker's key derived from address, having consecutive addresses on streets left side listed ascending and the right side descending (gas meter readouts). There were others, too, but, curiously enough, all I can remember are legacy data. I mean, data from legacy software, done in Cobol or Clipper.