Unified Information and Control Flow in Hierarchical Task Networks

Abstract

Much recent planning research has focused on two related issues. First, there has been a strong interest in information-gathering (or "sensing", or "knowledge- producing") actions. Second, there has been an investigation of plans with sophisticated control structures, such as conditional branches and loops. But the combination of these two lines of research poses a representational problem: plans with information-gathering actions that can be executed more than once can have complex information-flow and control-flow relationships. In this paper, we present a framework for the representation and execution of hierarchical plans with information producing actions, conditional branches, periodic actions, and loops. Our framework subsumes several techniques found in the recent literature.