Execution Monitoring and Schedule Revision for O-OSCAR: a Preliminary Report

This paper addresses the problem of maintaining the consistency of a pre-defined schedule during its execution in a real or simulated environment. This issue, referred to as Reactive Scheduling Problem, is known to be inherently difficult due to the usually strict timelines in which the revising procedure is called to react. Schedule revision must be quick, and sometimes solution quality must come as a secondary priority as the execution of the schedule does not allow for time-intensive computations. In this work we present a Schedule Execution Monitor and Control System which seizes upon the O-OSCAR (Object-Oriented SCheduling ARchitecture) scheduling tool, a constraint-based software architecture for the solution of complex scheduling problems. The core solving engine of O-OSCAR is represented by the ISES algorithm (Iterative Sampling Earliest Solutions), a constraint-based method for the solution of the RCPSP/Max problem (Resource Constrained Project Scheduling Problem with Time Windows). We have used the preceeding software architecture as a starting point to develop a Schedule Execution Monitor and Control System, capable of reactively maintaining the consistency of the schedule in spite of possible unexpected events to occur at schedule execution time. This paper describes this new module and the current idea of schedule revision also based on the ISES algorithm.