Integration of autonomous decentralized systems with different fault tolerance requirement levels

As the standardization of computers, networks and OS's has been going on and different systems can be easily connected physically, it is more preferable to integrate existing systems from an economical viewpoint. Under the changing requirements and situations, system engineering technologies to realize an individual user's requirements on a standard platform have become more important. Even when these application systems with respective user requirements are integrated together, the autonomy of each application system must be preserved to retain properties of online expansion, online maintenance and fault tolerance. It is shown that the Autonomous Decentralized System (ADS) architecture, originally developed to attain the online properties of the system, can be one solution to resolve the problem of integrating heterogeneous application systems while keeping each requirement level so that multiple systems have common architecture and different levels of fault tolerance requirements. The recursive model under the ADS architecture is proposed to integrate multiple systems while preserving the autonomy of each system. In addition, the gateway technique is designed to control the data flow between two different systems, not only by contents of the data but also by property levels of each system's requirement. This gateway technique based on the recursive model has been realized as the middleware on WINDOWS and UNIX and the heterogeneous ADS technique has been applied in the real application systems, and their effectiveness has also been shown.