Qualitative simulation of temporal concurrent processes using Time Interval Petri Nets

This paper presents a formalism called Time Interval Petri Nets (TIPNs), which are designed to support a qualitative simulation of temporal concurrent processes. One of the key features of TIPNs is a uniform use of time intervals throughout the model. This enables a natural and efficient representation of temporal uncertainty in inputs, outputs, and intermediate states of the qualitative simulation. This is required because the exact time of key events, such as the start time of a fire crisis, is typically not known with certainty. Likewise, output conclusions of the qualitative simulation include earliest time and guaranteed time of key events that can be used by a decision maker to select the most appropriate action. Results are described of a TIPN-based qualitative simulator constructed in the domain of ship damage control. The simulator was created to replace an existing quantitative simulator which was too slow to support envisionment-based real-time decision making in this domain. The experimental results showed a speedup of four to five orders of magnitude which enables hyper-real time qualitative prediction of consequences of multiple competing actions. An automated shipboard damage control decision-making system incorporating a TIPN-based qualitative simulator achieved a 318% improvement over human subject matter experts in a large-scale simulated exercise of over 500 scenarios.