Statecharts, transition structures and transformations

Statecharts are state-transition machines endowed with hierarchy on states and parallelism on transitions. It is shown that a statechart is described by a pair of relations over transitions (a transition structure), the former describing causality and the other describing a notion of asymmetric independence. A statechart can be effectively constructed from its transition structure. Transition structures corresponding to a subclass of Statecharts are characterized. Natural notions of morphisms among transition structures allow to define classes of statechart transformations which preserve behaviour.