HTN planning for information processing tasks

Abstract

This paper discusses the problem of integrated planning and execution for tasks that involve the consumption, production and alteration of relational information. Unlike information retrieval problems, the information processing domain requires explicit modelling of the changing information state of the domain and how the validity of resources changes as actions are performed. A solution to this problem is presented in the form of a specialised hierarchical task network planning model. A distinction is made between the information processing effects of an action (modelled in terms of constraints relating the domain information before and after the action) and the actions' preconditions and effects which are expressed in terms of required, produced and invalidated resources. The information flow between tasks is explicitly represented in methods and plans, including any required information-combining operations such as selection and union.

The paper presents the semantics of this model and discusses implementation issues arising from the extension of an existing HTN planner (SHOP) to support this model of planning.