Introducing Temporal Behaviour into Binary Decision Diagrams

Abstract Binary Decision Diagrams (BDDs) are an alternative technique used in the analyses of safety-critical system fault trees. BDDs have been found to produce the exact top-event probability more efficiently by reducing computing resources drastically. Unfortunately, this efficient technique is not used in the analysis of fault trees featuring sequential ordering of events. However, in the real world, the sequential ordering of events cannot be overlooked because it produces a more accurate evaluation of systems. We introduce a new technique, Temporal BDD (TBDD), that incorporates temporal behaviour – via Priority-AND gates – into BDDs. TBDD provides the exact results for both qualitative and quantitative analyses. However, unlike BDD, quantitative analyses cannot be performed on ‘unminimised’ cut sequences yet. It is hoped that this work will form the foundation for the full qualitative and quantitative analyses of Dynamic Fault Trees and Temporal Fault Trees in the near future.