> but with the added benefit that for the common case, you don't need any additional lookups. You only need to lookup CPR changes if you don't find the CPR that

> but with the added benefit that for the common case, you don't need any additional lookups. You only need to lookup CPR changes if you don't find the CPR that the user gave you Doing the CPR lookup ONLY when you don't find a record is really, really stupid. All you need is one bad cache, one database update that go rolled back and suddenly you've lost all recent updates the the user and will only see the bad record with no indication you've failed. Trying to use force changeable data into being a 'natural key' means that the number of edge cases you have to predict, write around and test for is going to rise significantly for no real benefit.