Computational complexity issues in operative diagnosis of graph-based systems

Systems that can be modeled as graphs, such that nodes represent the components and the edges represent the fault propagation between the components, are considered. Some components are equipped with alarms that ring in response to faulty conditions. In these systems, two types of problem are studies: fault diagnosis and alarm placement. The fault diagnosis problems deal with computing the set of all potential failure sources that correspond to a set of ringing alarms. Single faults, where exactly one component can become faulty at any time, are primarily considered. Systems are classified into zero-time and non-zero-time systems on the basis of fault propagation time. The latter are further classified on the basis of knowledge of propagation times. For each of these classes algorithms are presented for single fault diagnosis. The problem of detecting multiple faults is shown to be NP-complete. An alarm placement problem that requires a single fault to be uniquely diagnosed is examined