Handling contingency in temporal constraint networks: from consistency to controllabilities 论文

摘要

Temporal Constraint Networks (TCN) allow to express minimal and maximal durations between time-points. Though being used in many research areas, this model disregards the contingent nature of some constraints, whose effective duration cannot be decided by the system but is provided by the external world. We propose an extension of TCN based on the definition of the Simple Temporal Problem under Uncertainty (STPU) in which the classical network consistency property must be redefined in terms of controllability: intuitively, we would like to say that a network is controllable iff it is consistent in any situation (i.e. any assignment of the whole set of contingent intervals) that may arise in the external world. Three levels of controllability must be distinguished, namely the Strong, the Weak and the Dynamic ones. This paper provides a full characterization of those properties and their usefulness in practice, and proposes algorithms for checking them. Complexity issues an...