The devil's advocate cases: 1. When duplication occurs and goes unnoticed because the natural key isn't being used, and then perhaps the problem is "corrected"

The devil's advocate cases: 1. When duplication occurs and goes unnoticed because the natural key isn't being used, and then perhaps the problem is "corrected" by an administrator in a way that doesn't make sense. For example, someone sets up an account with an street address A, then forgets they had it and sets up an account with street address B. They call and complain that they can't find an old order, or whatever, and the duplication is discovered. The administrator later clobbers one of the addresses but both are in use. A natural key (behaviorally speaking) may have presented the duplication, assuming address isn't part of the natural key. This can be satisfied by uniqueness constraints, etc. 2. When you are browsing the database, you see a bunch of synthetic keys and have to perform various joins to be able to see the relevant data. The synthetic keys make joins easier to write, but make may make ad-hoc queries more time-consuming and difficult.