Decision approach to workload distribution

Abstract

Abstract. This paper deals with decisions of workload temporal distribution in scheduling discrete and diversified productions. A new way of formulating the scheduling problem is proposed, from which some concepts and tools are presented. The notion of time resource interval objects, TRIs, allows the management of technical (time and resource) aspects at the different levels of a hierarchical structuring of the set of decisions taken in the workshop, from ‘load distribution’ types, to ‘effective realization of the operations’ types. Constraint-based reasoning handles different TRIs corresponding to given kinds of decisions. It helps to highlight the bounds or limits to be respected while deciding, to remain consistent with an initial set of constraints, issued for example from an upper level of decisions. Decisions of load temporal distribution consist in readjustments of some time constraints on a set of planned operations, by taking into account the (or some more detailed) constraints on the resource(s) on which they have been planned, such as finite capacity and/or minimal profitability. The analysis on temporal proximities of the planned operations involves some particular structuring of the time axis into successive time intervals: these structures are associated with sets of temporal bounds, and are called adjacent decompositions of the time axis. Such a decomposition introduces some specific TRIs, associated with load constraints (coming from the planned operations), and resource constraints (coming from limited quantities of resource, or profitability concerns). By respecting the given time and resource constraints, they can ‘exchange’ some quantities of load according to communicating vessels processes. These phenomena have been modelled as bounded flows in a temporal network, and offer new flexible curves of load with finite capacities, to help the decision.