Simple Temporal Networks (STNs) allow minimum and maximum distance constraints between time-points to be represented. They are often used when tackling planning and scheduling problems that involve temporal aspects. This paper is a summary of the journal article "Time-dependent Simple Temporal Networks: Properties and Algorithms" published in RAIRO - Operations Research. This journal article introduces an extension of STN called Time-dependent STN (TSTN), which covers temporal constraints for which the temporal distance required between two time-points is not necessarily constant. Such constraints are useful to model time-dependent scheduling problems, in which the duration of an activity may depend on its starting time. The paper introduces the TSTN framework, its properties, resolution techniques, as well as examples of applications.

Earth observation satellites are space sensors which acquire data, compress and record it on board, and then download it to the ground. Because of the use of more and more sophisticated compression algorithms, the amount of data resulting from an acquisition is more and more unpredictable. In such conditions, planning satellite data download activities offline on the ground is more and more problematic. In this paper, we report the results of a work aiming at evaluating the positive impact of planning downloads onboard when the amount of data produced by each acquisition is known. The data download problem to be solved on board is an assignment and scheduling problem with unsharable resources, precedence constraints, time-dependent minimum durations, and a complex optimization criterion. The generic InCELL library is used to model constraints and criterion, to check non temporal constraints, to propagate temporal constraints, and to evaluate the criterion. On top of this library, greedy and local search algorithms have been designed to produce download plans with limited time and computing resources available on board.

This paper presents a generic anytime forward-search constraint-based algorithm for solving planning problems expressed in the CNT framework (Constraint Network on Timelines). It is generic because it allows many kinds of search to be covered, from complete tree search to greedy search. It is anytime because some parameter settings, together with domain-specific knowledge, allow high quality plans to be produced very quickly and to be further improved. It is forward because it systematically considers the decisions to be made in a chronological order. It is finally constraint-based because it is built on top of the CNT framework which is an extension of the CSP framework able to model discrete event dynamic systems and because it is implemented on top of the Choco constraint programming tool from which it inherits all the constraint handling machinery. Experimental comparisons are made in terms of quality profile with other domain-dependent and domain-independent planners.