In this paper we report on a work in progress assessing the faults observed and reported in a distributed, safety-critical, largely embedded system with both electrical and mechanical components. We illustrate why standard software testing techniques are not sufficient and indicate some of the technical and non-technical problems encountered in examining the faults and the initial results obtained. While the application domain is elevator operation, the techniques described here are general enough to apply to many other domains. Much of the data analyzed here would be considered imprecise in the software industry if it were used in software testing or to help increase fault tolerance. The paper includes a discussion of the use of multiple views of data, assessment of missing data, and analysis of informal information to produce its conclusions about fault avoidance and fault tolerance.
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