A design of an Ada IPC (Inter-Program Communication) interface is proposed, through which a designer of distributed systems can (a) specify arbitrary data types needed for inter-program communication and (b) use parallel programming features to build highly parallel systems; a test simulator was built for execution of the IPC interface and a multi-window system was realized as an application of the interface on the simulator; the interface was found to be useful, making description of inter-program communication simpler and easier.