The O-Plan Constraint Associator

O Plan is a command planning and control architecture which has an open modular structure intended to allow experimentation on or replacement of various components The research is seeking to isolate functionality that may be generally required in a number of applications and across a number of di erent planning scheduling and control systems The aim of this paper is to describe the Constraint Associator which is resident in the database manager which looks after the plan state and which forms a new core components of the O Plan architecture The constraint Associator mediates between the decisions made by the decision making parts of the architecture i e knowledge sources and the underlying constraint managers This paper describes the motivation for the development of the constraint associator and the way in which plan constraints are represented and handled in the O Plan architecture It gives details of a rational reconstruction of the constraint management interfaces which were needed to support the constraint associator These guidelines are now being used as a design principle within the latest version of O Plan The cooperative manipulation of constraints on plans by a user and by the capabilities pro vided in computer systems provides a useful and natural paradigm for e ective planning and scheduling support systems The provision of powerful computer based constraint management languages and tools could lead to a rapid expansion of the bene ts to be gained by identifying more standard ways in which constraints can be handled in future planning and scheduling systems The paper concludes with a description of a planning agent whose architecture and components would make it suitable across a number of planning and representation domains The O Plan Constraint Associator O Plan the Open Planning Architecture The O Plan Project at the Arti cial Intelligence Applications Institute of the University of Edinburgh is exploring a practical computer based environment to provide for speci cation generation interaction with and execution of activity plans O Plan is intended to be a domain independent general planning and control framework with the ability to embed detailed knowledge of the domain See for background reading on planning systems See for details of O Plan now referred to as O Plan the planning system that was a forerunner to the O Plan agent architecture That paper also includes a chart showing how O Plan relates to other planning systems The O Plan system combines a number of techniques A multi agent approach to strategic task assignment tactical planning elaboration and operational plan execution support A control architecture within each agent in which each control cycle can post further processing steps on an agenda which are then picked out and processed by appropriate handlers Knowledge Sources The uniform treatment of the user in the role of planner and computer based planning capabilities as Knowledge Sources The notion of a Plan State which is the data structure containing the emerging plan the aws remaining in it and the information used in building the plan A hierarchical planning system which can produce plans as partial orders on actions Constraint posting and least commitment on object variables Temporal and resource constraint handling using incremental algorithms which are sen sitively applied only when constraints can alter O Plan is derived from the earlier Nonlin planner from which it takes and extends the ideas of Goal Structure Question Answering Truth Criterion and typed conditions We have extended Nonlin s style of task description language Task Formalism tf O Plan is aimed to be relevant to the following types of problems project management for product introduction systems engineering construction process ow for assembly integration and veri cation etc planning and control of supply and distribution logistics mission sequencing and control of space probes and satellites such as voyager ers etc The O Plan Constraint Associator A user speci es a task that is to be performed through some suitable interface We call this process task assignment A planner plans and if requested arranges to execute the plan to perform the task speci ed The execution system seeks to carry out the detailed activities speci ed by the planner while working with a more detailed model of the execution environment Task Assign Capability Domain Model Planner Capability Domain Model Exec System Capability Domain Model Plan State Plan State Plan State R R R Task Assign Planner Exec System User Requirements Reporting Requirements