DISA : an interactive scheduler using abstractions

A major challenge in the area of global market economy is to develop new techniques for solving real world scheduling, planning, logistic and resource allocation problems. Indeed, any industrial organisation can only be economically viable by maximising customer services, maintaining efficient, low cost operations and minimising total investment. Significant domains exhibiting these characteristics are manufacturing, distribution logistics, hospital, airline management and manpower management. Effective integration of the tasks planning, scheduling and resource allocation is a key to achieve successful resource management. Distributed systems, such as cooperative distributed problem solvers, have been shown to be a promising approach. They have been introduced in the domains of manpower management and manufacturing where basics of Distributed Artificial Intelligence, such as contract net protocol or global/local planning, have been studied [1]. Following are the more recent of the systems: DAS [2], CORTES [3], ReDs [4] and ADDYMS [5]. All of them use a multi-agent architecture to address the problem of manufacturing scheduling. However, none of these systems link the task of planning, scheduling and resource allocation into one structure in order to provide the necessary communication of problems, solutions and advise between the different processes. In complex distributed problem solving, it is often achieved via a multi-layered structuration corresponding to refinements in problem analysis. In computer vision for instance, it is to consider an image globally to extract some interesting parts and then to focus the system attention on those parts to analyse them in more details. Agents in such architectures then introduce a distribution according to spatial parameters. We propose, for the fields we are interested in, to distributed agents according to temporal parameters, extending the idea of modelling the problem according to a temporal constraint tree, see [4], for the integration of planning, scheduling and secondary resource allocation within a multi-agent architecture. Like DAS, the DISA system (Distributed Interactive Scheduling with Abstractions), described in this paper, use a hierarchical architecture where agents, distributed according to the temporal parameter, are heterogeneous in behaviours and functionnalities, to better address environmental uncertainty. The hierarchy, dependant on problem solving functionality over time rather constraint influence over time, will be presented in the framework of an application dedicated to the scheduling of operations in an hospital.