Two tools for engineering analyses of highly reliable systems, one for quantitative reliability evaluation and the other for fault diagnosis, have been developed based on an object-oriented representation of fault trees. The fault trees serves as a central knowledge base for the integrated tool set, ensuring that consistent design information is used in both procedures. The tools have a graphical interface for data entry and the display of results, and enable the engineer to modify system models easily and understand the effects of the changes quickly. The availability of the models in an accessible form improves the design process by eliminating redundant model development in various stages of the lifecycle. The object-oriented models are particularly useful since they are easily modified to characterize various aspects of system behavior, promoting the development of additional analysis tools that will access the same knowledge base. The proposed approach is illustrated with reference to a representative subset of the Space Station Freedom data management system, which consists of three subsystems connected by a token ring network