Uniied Information and Control Flow in Hierarchical Task Networks

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, 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 represen-tational problem: plans with information-gathering actions that can be executed more than once can have complex information-ow and control-ow 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.