Distributed management for software maintenance in a wide-area railway system

In a large scale real time control system, functions of subsystems differ slightly although they seem to be identical. Functions change when hardware is replaced or when the function itself is upgraded. If the standard system is generated by merging the differences and is installed then to each subsystem, subsystems become different with maintenance being carried out in each subsystem to fit its operational conditions. Furthermore, subsystems are distributed in a wide area. Software maintenance therefore becomes very difficult. The paper describes a distributed management for software maintenance in the Tokyo metropolitan area railway system. This management has two phases: generating programs for making maintenance easy and executing programs for increasing the reliability of the system. There it contributes to the effectiveness of maintenance and increases the reliability of the total system.