Reducing memory requirements in reachability-based finite automata operations

New applications of finite automata, such as computational linguistics and asynchronous circuit simulation, can require automata of millions or even billions of states. All known construction methods (in particular, the most effective reachability-based ones that save memory, such as the subset construction, and simultaneously minimizing constructions, such as Brzozowski's) have intermediate memory usage much larger than the final automaton, thereby restricting the maximum size of the automata which can be built. In this paper, I present a reachability-based optimization which can be used in most of these construction algorithms to reduce the intermediate memory requirements. The optimization is presented in conjunction with an easily understood (and implemented) canonical automaton construction algorithm. Copyright (C) 2003 John Wiley Sons, Ltd.