Integrating Off-line and On-line Scheduling Approaches

Solving a scheduling problem consists in finding an initial solution able to model all the complex constraints that relate the problem activities. Moreover, the solving process should be necessarily considered as propaedeutic for the next phase of any schedule’s life: its execution in the real world. The inherent unpredictability of real working environments poses serious difficulties to which the scheduling community normally responds by (1) introducing methodologies that tend to increase schedule robustness (off-line phase, proactive approach), and by (2) developing fast-reaction techniques to be employed during schedule execution (on-line phase, reactive approach). In the previous edition of this workshop we presented a benchmark generator for the reactive scheduling problem. This problem consists in monitoring the execution of a schedule and repairing it every time it is deemed necessary. The main motivation behind our previous work came out from the recognized lack (hence the necessity) of benchmark sets for this specific problem. In this paper we provide an empirical study based on the same benchmark generator which focuses on the mutual interactions among a set of off-line and on-line constraint-based scheduling approaches. We devise a set of closed loop execution management algorithms, and compare their behavior within an experimental framework which allows to directly assess the consequences of each chosen strategy combination, through simulated schedule executions. A number of interesting results are described that open new perspectives for future work based on this integrated schema.