Decision-aid in job shop scheduling: A knowledge based approach

This paper deals with operation scheduling on machines in a job shop. The jobs which consist of a set of related operations are supposed to be constrained by limit times (earliest starting times and due dates). The approach aims at generating restrictions on local scheduling decisions by only considering limit times and resource availability constraints (constraint based analysis). This is achieved through an inference process which is defined from generic knowledge arising in scheduling problems : limit times associated with each operation, logical sequencing conditions between operations, inference rules relating to limit times and sequencing conditions. A software implementation in PROLOG of a constraint-based analysis module is presented. Such a module may be used either in a static way in order to generate a plan over a certain horizon or in a dynamic way in order to help in making real time decisions. In this last case it can be held to act the part of a flexible planning function.