Implicit shift scheduling with multiple breaks and work stretch duration restrictions

This paper considers a shift scheduling problem that includes different forms of flexibility in terms of shift starting times, break lengths and break placement. Two particular forms are studied: fractionable breaks and work stretch duration restrictions. For some instances the use of fractionable breaks results in considerable labor savings. In addition, imposing work stretch duration restrictions is a very convenient approach to place multiple breaks within a shift. In this context, we show the merits of using so-called forward and backward constraints to model work stretch duration restrictions. We also introduce a new formulation of the forward and backward constraints and demonstrate that it considerably reduces the density of the constraint matrix of both models.