We formalize the rigorous but informal description of the semantics of statecharts given by Harel and Naamad in [3] which corresponds to the semantics underlying the commercial tool STATEMATE. We closely follow [3] to increase confidence that our semantics actually corresponds to their informal description. In [3] the semantics is given by a detailed description of the so-called basic step algorithm. Based on a formalization of this basic step algorithm we associate to each statechart a transition system which defines its computations. This is the first step towards linking the language of statecharts as supported by STATEMATE with other automatic verification tools. Our formalization uses Z notation rather than "standard mathematics". This allows to structure the definition of the formal semantics and to use tools like type-checkers.

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We present a software development method for event-triggered sequential systems, where we extend a widely used formal Z technique to specify also different kinds of activation of operations and the availability of input and output values. Beside the system operations we also specify the operations of the environment. A data flow diagram serves to specify where an operation belongs to. We define a formal semantics for such specifications by a translation to fair transition systems. Requirements can then be expressed in linear temporal logic. We apply our formal method to a lift already specified with the Z technique and detect a specification fault indicating a drawback of the Z technique for which we suggest a solution.