Towards Mixed Planning and Scheduling

The conventional wisdom and practice is that planning and scheduling tasks are solved separately using different methods and approaches. However, recent development in industrial planning and scheduling demands for mixing both tasks to allow modelling of wider class of problems. The purpose of this paper is to present a framework for mixing planning and scheduling tasks within single system. We analyse traditional views of planning and scheduling and we highlight the drawbacks of separating both tasks when applied to modelling complex process environments. We give some real-life examples where the mixed approach helps to model the problems and we propose a generic framework for such mixture. We also argue for using constraint programming as underlying solving technology and, finally, we describe some constraint models based on the proposed framework. Although, we concentrate on planning and scheduling in complex process environments we believe that the results contribute to both planning and scheduling communities in general.