Unified 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 "knowledgeproducing") 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 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.