Bridging the Gap between Fault Trees and UML State Machine Diagrams for Safety Analysis

Poorly designed software systems are one of main causes of accidents in safety-critical systems, and thus, the importance of safety analysis for software has greatly increased over the recent years. Software safety can be improved by analyzing both its desired and undesired behaviors, and this in turn requires expressive power such that both can be modeled. However, there is a considerable gap between modeling methods for desired and undesired behaviors. Therefore, we propose a method to bridge the gap between fault trees (for undesired behavior) and UML state machine diagrams (for desired behavior). More specifically, we present rules and algorithms that facilitate the transformation of a hazard (in the context of fault trees) to a UML state machine diagram. We illustrate our proposed approach via an example on a microwave-oven system. Our proposed transformation can help engineers identify how the hazards may occur, thereby allowing them to prevent the hazard from occurring.