Incremental design of statechart specifications

We present a Statecharts dialect with only three syntactic constructs and a semantics that is not restricted to describe reactive systems on an implementation level but allows to model them on an abstract, more specification oriented stage, where design alternatives are still left open. We give a refinement calculus with rules that tell the designer how to come from the abstract specification to the implementation such that the system under development only becomes more concrete but not more abstract; under-specification is eliminated by adding more information. The result of a design process that follows these rules is an implementation that satisfies its specification by construction.