Failures: Their Definition, Modelling and Analysis

This paper introduces the concept of a ‘structured occurrence net’, which as its name indicates is based on that of an ‘occurrence net’, a well-established formalism for an abstract record that represents causality and concurrency information concerning a single execution of a system. Structured occurrence nets consist of multiple occurrence nets, associated together by means of various types of relationship, and are intended for recording either the actual behaviour of complex systems as they interact and evolve, or evidence that is being gathered and analyzed concerning their alleged past behaviour. We provide a formal basis for the new formalism and show how it can be used to gain better understanding of complex fault-error-failure chains (i) among co-existing interacting systems, (ii) between systems and their sub-systems, and (iii) involving systems that are controlling, supporting, creating or modifying other systems. We then go on to discuss how, perhaps using extended versions of existing tools, structured occurrence nets could form a basis for improved techniques of system failure prevention and analysis.