[4] SANDERS W H, MEYER J F. Reduced base model construction methods for stochastic activity networks［J］. Selected Areas in Communications, 1991, 9(1): 25-36.
[5] BOOCH G, DOUGLASS B, CERNOSEK G. Unified mo-deling language for real-time systems design［M］. California：Ratinal Software Corporation, 1996: 1-10.
[6] VAN DER AALST W M P. Formalization and verification of event-driven process chains［J］. Information and Software Technology, 1999, 41(10): 639-650.
[7] PETERSON J L. Petri net theory and the modeling of sytems［M］. London：Prentice-Hall 1981: 1-21.
