PASSAT: A User-centric Planning Framework Karen L. Myers 1 W. Mabry Tyson 1 Michael J. Wolverton 1 Peter A. Jarvis 1 Thomas J. Lee 1 Marie desJardins 2 1 Artificial Intelligence Center SRI International 333 Ravenswood Avenue Menlo Park, California 94025 {myers,tyson,mjw,jarvis,tomlee}@ai.sri.com 2 University of Maryland, Baltimore County Dept. of CS and EE 1000 Hilltop Circle Baltimore, MD 21250 mariedj@cs.umbc.edu Abstract We describe a plan-authoring system called PASSAT (Plan- Authoring System based on Sketches, Advice, and Templates) that combines interactive tools for constructing plans with a suite of automated and mixed-initiative capabilities designed to complement human planning skills. PASSAT is organized around a library of predefined templates that encode task networks describing standard operating procedures and previous cases. Users can select from these templates to apply during plan development, with the system providing various forms of automated assistance. A mixed-initiative plan sketch facility helps users refine outlines for plans to complete solutions, by detecting problems and proposing possible fixes. An advice capability enables user specification of high-level guidelines for plans that the system helps to enforce. Finally, PASSAT includes process facilitation mechanisms designed to help a user track and manage outstanding planning tasks and information requirements, as a means of improving the efficiency and effectiveness of the planning process. PASSAT is designed for applications for which a core of planning knowledge can be captured in predefined action models but where significant user control of the planning process is required. Introduction AI planning technology provides powerful tools for solving problems that require the coordination of actions in the pursuit of specified goals. To date, however, there has been limited success in transitioning this technology to significant applications in the commercial, military, or space sectors. A major obstacle to technology transfer lies with the lack of control available to potential users of planning systems. AI planning systems have traditionally been designed to operate as black boxes: they take a description of a domain and a set of goals and automatically synthesize a plan for achieving the goals. Human planners, however, are generally reluctant to cede full control to automated planning systems in this manner. Many potential consumers of planning technology require more user-centric tools that are designed to augment human skills rather than replace them. This observation has led, in recent years, to the development of a number of plan-authoring frameworks. Plan-authoring systems provide a set of plan editing and manipulation capabilities that support users in developing plans. These systems introduce a degree of structure to the planning process, yielding principled representations of plans with well-defined semantics. Plan-authoring systems can include a range of planning aids that reason over this structure; however, the role of such automated aids is to augment human planning skills by facilitating human- driven plan development. Interest in plan-authoring systems is strong within both the space and military sectors, for their potential to improve the quality and process of plan development without incurring the high knowledge modeling costs and loss of control associated with fully automated planning systems. This paper describes a plan-authoring system called PASSAT (Plan-Authoring System based on Sketches, Advice, and Templates) designed to support user-centric planning. At its heart, PASSAT is a plan-authoring system in which users construct and modify plans interactively. Users can draw upon a library of templates, to the extent they desire, to assist with plan development. Templates correspond to a form of hierarchical task network (HTN) [Tate, 1977], and may encode both parameterized standard operating procedures and cases corresponding to actual or notional plans developed for related tasks. To complement these interactive tools, PASSAT includes a range of automated and mixed-initiative planning capabilities. Users can invoke an automated planning mode based on standard HTN methods to expand any open task within a plan. A plan sketch facility enables users to create outlines of plans that are then filled out using templates designed for similar tasks. Advice within PASSAT enables users to define high-level policies to be satisfied by both plans and planning processes. Such guidance can be useful both in directing automated components within the system, and in tracking high-level guidelines that a user wants satisfied but may inadvertently violate through his interactive planning choices. PASSAT also includes process facilitation mechanisms designed to aid the user in managing plan development. These mechanisms help the user track open tasks and