1. A method for generating a reduced state space representation for a model in a compositional state system, the model comprising a selected set of components, each component comprising one or more states and one or more events, the model comprising interactions associated with events, the reduced state space representation being defined with respect to a set of events of interest selected from the events in the set of components the method comprising the following steps: a. for each component in the set of components, defining a transitive effect machine for the component such that the states of the transitive effect machine represent the states of the component and the events of the transitive effect machine represent the transitive effects of interactions associated with transitions of the component, the transitive effects being defined relative to the set of components, and the set of events of interest, and b. reducing each of the defined transitive effect machines, the reduction including the classification of states within a single transitive effect machine to permit a set of states in the said transitive effect machine to be grouped into a single class when each state in the said set of states is characterized by common properties with respect to the set of events of interest.