A Practical Temporal Constraint Management System for Real-Time Applications

A temporal constraint management system (TCMS) is a temporal network together with algorithms for managing the constraints in that network over time. This paper presents a practical TCMS, called MYSYSTEM, that efficiently handles the propagation of the kinds of temporal constraints commonly found in real-time applications, while providing constant-time access to "all-pairs, shortest-path" information that is extremely useful in many applications. The temporal network in MYSYSTEM includes special time-points for dealing with the passage of time and eliminating the need for certain common forms of constraint propagation. The constraint propagation algorithm in MYSYSTEM maintains a restricted set of entries in the associated all-pairs, shortest-path matrix by incrementally propagating changes to the network either from adding a new constraint or strengthening, weakening or deleting an existing constraint. The paper presents empirical evidence to support the claim that MYSYSTEM is scalable to real-time planning, scheduling and acting applications.