Planning and Acting While the Clock Ticks

Standard temporal planning assumes that planning takes place offline and thenexecution starts at time 0. Recently, situated temporal planning wasintroduced, where planning starts at time 0 and execution occurs after planningterminates. Situated temporal planning reflects a more realistic scenario wheretime passes during planning. However, in situated temporal planning a completeplan must be generated before any action is executed. In some problems withtime pressure, timing is too tight to complete planning before the first actionmust be executed. For example, an autonomous car that has a truck backingtowards it should probably move out of the way now and plan how to get to itsdestination later. In this paper, we propose a new problem setting: concurrentplanning and execution, in which actions can be dispatched (executed) beforeplanning terminates. Unlike previous work on planning and execution, we musthandle wall clock deadlines that affect action applicability and goalachievement (as in situated planning) while also supporting dispatching actionsbefore a complete plan has been found. We extend previous work on metareasoningfor situated temporal planning to develop an algorithm for this new setting.Our empirical evaluation shows that when there is strong time pressure, ourapproach outperforms situated temporal planning.