Interaction between reactive and deliberative tasks for on-line decision-making

To get actual autonomous engines or systems, it is necessary to equip them with on-line decision-making mechanisms: computation of decisions that fit the current situation, performed in parallel with real execution. However, such a computation introduces a contradiction between requirements on the quality of the decision and on the time at which it will be delivered. This contradiction is all the stronger as decisionmaking may require intensive computing whose duration is not very well controlled. The solutions that are proposed in the literature to overcome this contradiction are often unsatisfactory, either from the point of view of the quality requirements, or from the one of the temporal requirements, most of the time from the one of the organisation and validation of the whole decision-making mechanism. In this paper, we propose a generic schema for the interaction between reactive and deliberative tasks for on-line decisionmaking. The basis of this schema is a control of decisionmaking by reactive tasks, which may call for anytime deliberative tasks. We show an implementation of this schema using the synchronous Esterel language for the programming of the reactive tasks and the Java language for the programming of the deliberative ones. The proposed schema is illustrated on an example of on-line management of observation tasks performed by an Earth detection and observation satellite. We conclude with a synthesis of the advantages of the proposed