The active index can be readily implemented using the SIS Testbed, which is a component-based software engineering environment. Each index cell corresponds to a component. The messages for the active index system correspond to messages for the SIS Testbed. The f function for defining appropriate input messages, and the g function for defining output messages to appropriate output index cells, actions and next state, are embedded in the codes for the individual components. In particular, some index cells may correspond to super-components.