Search Strategies for Scheduling Problems with Optional Activities

Scheduling problems typically deal with activity sequencing and resource allocation while the problem of activity selection is assumed to be resolved before scheduling. To increase flexibility of scheduling systems in complex environments, it is possible to include activity selection, for example decisions about alternative process routes, in the scheduling problem. This could be realized by assuming optional activities in the problem specification. Constraint-based scheduling seems to be a good underlying technology to model problems both with traditional scheduling decisions such as activity sequencing and resource allocation, and with planning-like decisions such as selection among alternative activities. The paper studies search strategies for solving scheduling problems with optional activities – the search procedure assumes both sequencing decisions and selection among alternative activities.