Modeling timing behaviors of systems and verifying timing constraints again
st the model are major tasks in developing real-time systems, However, it i
s recognized to be extremely difficult to predict the timing behavior of sy
stems precisely in the requirements phase. Timing uncertainty, if not consi
dered properly in the modeling and verifying steps, may incur subtle, yet c
ritical errors in final products. We propose a method of dealing with such
timing uncertainty using an extended duration calculus formalism. The exten
ded duration calculus, named fuzzy duration calculus, allows us to specify
uncertain timing behavior of the system using the fuzzy theory. Semantics a
nd proof system of the duration calculus are redefined in order to accommod
ate fuzzy concepts. Based on the semantics and proof system, we can verify
timing constraints against the system model. A portion of nuclear power pla
nt (NPP) control system is employed to demonstrate the feasibility and the
effectiveness of our approach. (C) 2000 Elsevier Science Inc. All rights re
served.