Abstract:Based on the previous work about verification problem projection according to the safety requirements, a variable reduction approach was proposed based on causal relation for the projected subproblems. First, the causal relations among the environment variables of the projected subproblems were defined. Then, the basic causal relation combination of variables and the reduction rules were concluded. Through variable reduction, the state space of the verification problem was reduced. Finally, with configuration of a domestic metro line, an experiment of modeling and verification was demonstrated to show that the variable reduction approach efficiently reduces the verification complexity.