Cyclical Staff Scheduling Using Constraint Logic Programming

In organizations where duty is around the clock, 7 days a week and every week of the year, timetabling is a very difficult task, juggling between the workload and the constraints to be respected. Our work concerns cyclical timetabling. This is not just duplicating a fixed sequence of assignments, but has to consider fixed annual leave, and various regulations on assignments on successive days. In some cases, the cycle sequence has to be relaxed and cycle length shortened or extended. In other cases, a small change in leave dates is allowed, except in summer. This paper describes the context and the use of work cycles in the real world, proposes an abstract model to take into account the various constraints, and finally show how to implement an effective solution using Constraint Logic Programming (in particular, CHIP V5) to produce timetables of up to 150 people over a yearly horizon.