Optimizing Hierarchical, Concurrent State Machines in Umple for Model Checking

This paper presents our work on the optimization of hierarchical, concurrent state machines for the purpose of model checking software systems. We propose an encoding strategy that reduces the explosion of the state space during model checking. Our method removes non-concurrent composite states of a state machine but retains its concurrent and basic states counterparts. Transitions into and those originating from the removed states are redirected in a manner that is semantics-preserving. The resulting state machine has a state-space lesser than (or equal to) its unoptimized version. This in-turn yields improvements in resource utilization as attested by means of case studies. While cone of influence (COI) reduction remains a potent method for managing state space explosion during model checking, it was discovered that our approach outperforms COI on some parameters. It even facilitates further reduction in resource utilization when combined with COI.