Abstract: A system for employing a computer to control a device to provide a plurality of services for a plurality of entities. Each entity corresponds to exactly one of the services and each service has its own copy of the code which defines the service. The system associates a process which executes the service with each service. The code for a service defines a finite state machine which is continually executed by the service's process. While in a given state, the finite state machine may traverse a decision graph which is directly accessible to the process. Actions to be taken on traversal of a node of the decision graph may be defined in the finite state machine. The service's process communicates with other processes and with itself by means of interprocess messages. Each state of the finite state machine contains event handlers for responding to messages received by the service's process.