Implementation of Resource Constraints in ILOG SCHEDULE: A Library for the Development of Constraint-Based Scheduling Systems1

It has been argued that the use of constraint-based techniques and tools enables the implementation of precise, flexible, efficient and extensible scheduling systems: precise and flexible as the system can take into account any constraint expressible in the constraint language; efficient inasmuch as highly optimized constraint propagation procedures are now available; extensible as the consideration of a new type of constraint may require (especially in an object-oriented framework) only an extension to the constraint system or, in the worst case, the implementation of additional decision-making modules (without needs for modification of the existing code). The following paper presents ILOG SCHEDULE, a C++ library enabling the representation of a wide collection of scheduling constraints in terms of "resources" and "activities." ILOG SCHEDULE is based on SOLVER, the generic software tool for object-oriented constraint programming developed and marketed by ILOG. SOLVER variables and constraints can be accessed from SCHEDULE activities and resources. As a result, the user of SCHEDULE can make use of SOLVER to represent specific constraints, and implement and combine the specific problem-solving strategies that are the most appropriate for the scheduling application under consideration. It is hoped — and expected — that object-oriented constraint programming tools like SCHEDULE will enable the industry to make decisive steps toward the implementation of "state of the art," highly flexible, constraint-based scheduling applications. 1 In: Intelligent Systems Engineering, 1994, 3, (2), pp. 55-66.