Predicate-Transition Net Reachability Testing Using Heuristic Search

Given two markings M0 and Mg on a predicate-transition (pr/t) net, finding a firing sequence which transforms M0 to Mg is called the reachability test problem. Once a problem in the real world has becn modeled as a pr/t net, a solution of the problem can be, in most cases, directly obtained from performing a reachability test on the pr/t net model. However, as a problem with exponential complexity, there does not exist an efficient algorithm to perform the reachability test. One method which might be used in solving such a problem is heuristic search. The efficiency and effectiveness of a heuristic search algorithm is dependent upon its heuristic function. We have found several admissible and monotonic heuristic functions which can be used to solve the reachability test problem. We have implemented an iterative deepening A* algorithm using our heuristic functions, and present the experimental results for our heuristics.