A system for employing a computer to control a device to provide a plurality of services (207) for a plurality of entities (205). Each entity corresponds to exactly one of the services and each service has its own copy (213) of the code which defines the service. The system associates a process (113) 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. The finite state machine is defined by a special language, the service logic language, and the decision graphs are defined by means of a graphical editor. The compiler for the service logic language produces not only C++ code defining the finite state machine, but also data base and shell scripts which are used to provision and maintain the services. An embodiment of the system is disclosed which is used in a service node of a telephone switching network to provide telephone services such as 800 number service, caller ID, and the like.