Interactive system with state manager subsystem

Abstract

An interactive system has a component which manages interactions with the user and a component which manages data transformations. Communication between the interactive component and the data transformation component is by means of a state manager component. The state manager component includes an expected state description, which describes operation of the interactive system as a set of states and transitions therebetween, and an active state description, which describes as much of the present and past state of the interactive system as is required to determine the next state and to 'back out' of the present state is response to user inputs specifying 'cancel' or 'undo' operations. Routines in the state manager interpret the expected state description and the active state description in response to inputs from the interactive component and the data transformation component, and as determined by the inputs and the state descriptions, the routines perform a transition to a new state and produce an output to the interactive component or the data transformation component. In the state model used in the state descriptions, initiating a state involves determining whether any conditions for entry have been fulfilled and activating substates, while completing a state involves determining whether any conditions for exit from the state have been fulfilled and determining the state to which a transition is to be attempted.