An HTN Planner That can Reason About Time

Abstract

In this paper we present a formalism for explicitly representing time in HTN planning. Actions can have durations and intermediate effects in this formalism. Methods can specify qualitative and quantitative temporal constraints on decompositions. Based on this formalism we defined a planning algorithm TimeLine that can produce concurrently executable plans in the presence of numeric state variables. We state and prove the soundness of the algorithm. We also present the experimental results of the TimeLine implementation that shows the feasibility of our approach. UMIACS-TR-2002-105