An Algorithm for Checking the Dynamic Controllability of a Conditional Simple Temporal Network with Uncertainty - Revisited

Abstract

A Simple Temporal Network with Uncertainty (STNU) is a framework for representing and reasoning about temporal problems involving actions whose durations are bounded but uncontrollable. A dynamically controllable STNU is one for which there exists a strategy for executing its time-points that guarantees that all of the temporal constraints in the network will be satisfied no matter how the uncontrollable durations turn out. A Conditional Simple Temporal Network with Uncertainty (CSTNU) augments an STNU to include observation nodes, the execution of which incrementally and dynamically determines the set of constraints that must be satisfied. Previously, we generalized the notion of dynamic controllability to cover CSTNUs and presented a sound algorithm for determining whether arbitrary CSTNUs are dynamically controllable. That algorithm extends edge-generation/constraint-propagation rules from an existing DC-checking algorithm for STNUs with new rules required to deal with the observation nodes. This paper revisits that algorithm, modifying some of its rules to cover more cases, while preserving the soundness of the algorithm.