Each userGap object has a descriptive name composed by the name of the associated user, the reason of the gap and the gap starting date. Each userGap has also a short descriptive name composed by just the reason of the gap and the gap starting date.

There cannot be two userGap for the same user with the same reason and start date-time - i.e. the combination of the user, the reason and the start date-time is the unique key for userGap.