Model based fault isolation for object-oriented control systems

This report addresses the problem of fault propagation between software modules in a large industrial control system with an object oriented architecture. There exists a conflict between object-oriented design goals such as encapsulation and modularity, and the possibility to suppress propagating error conditions. When an object detects an error condition, it is not desirable to perform the extensive querying of other objects that would be necessary to decide how close to the real fault the object is and hence whether it should report to the user. The fault propagation manifests itself as many irrelevant error messages thus causing problems for system operators and service personnel trying to quickly iso-late the real fault. A system developer with insight in the system design, can, of course, often easily interpret the multitude of error messages from a fault scenario and isolate the primary cause. The key observation is that this can often be done using high-level models of the system and the fault propagation. We have made an eort to automate this procedure, and we propose a fault isolation scheme as a