FUNCTION-BASED MODELING AND TROUBLESHOOTING

Abstract

Abstract This report describes an ongoing effort to apply the functional modeling (FM) approach to the representation of and reasoning about engineered artifacts. The application domain is the external active thermal control system (EATCS) of space station Freedom. The intuitions behind FM are threefold. First, knowing the purposes of a device allows organization of the causal understanding of how a device works. Second, causality may be represented in modular chunks, which are indexed by the purposes of the device and its interrelated subsystems. Finally, the global behavior of a device in a given situation can be understood by composition of the relevant causal net fragments. These starting intuitions provide a framework for organizing calculations about a device and for performing a limited type of simulation with the organized ensemble. Parallel to the FM modeling effort for EATCS is the development of a methodology that generates diagnostic knowledge for a device directly from its FM representation. This knowledge compilation strategy takes the FM representation of the target device and compiles organized knowledge structures for troubleshooting. The knowledge structures are utilized in two ways for diagnosis: (1) efficient hypothesis generation and (2) hypothesis evaluation. The central result of the research reported here is that an FM representation of a device can be used to generate knowledge for diagnostic troubleshooting.