A Novel Parsing-based Approach for Verification of Hierarchical Plans

Hierarchical Task Networks were proposed as a method to describe plans by decomposition of tasks to subtasks until primitive tasks, actions, are obtained. Valid plans - sequences of actions - must adhere both to causal dependencies between the actions and to the structure given by the decomposition of the goal task. Plan verification aims at finding if a given plan is valid, that is, if it is causally consistent and it can be obtained by decomposition of some task. The paper describes a novel parsing-based approach for hierarchical plan verification that is orders of magnitude faster than existing methods.