Fault Tree Analysis with Moby/FT

Fault tree analysis (FTA) is a standardised technique used by engineers to explore possible failure states of safety-critical systems. Since the FTA is generally practised informally and thus, it cannot be guaranteed that it is applied correctly, several formal approaches have been introduced in the past (e.g. [STR02]) for allowing engineers to verify that they built a fault tree considering the right events (correctness) and that they did not forget a relevant event (completeness). But without automated proof support the acceptance of such formal approaches in industry is insufficient. In this paper we present the tool Moby/FT, which offers a graphical editor for specifying and verifying fault trees. The aim of Moby/FT is to increase the reliability of real-time systems, which are often profoundly safety-critical. The tool allows the user to specify fault trees together with the semantics of their events in terms of an interval logic, Duration Calculus [ZH04], and to automatically verify the correctness and completeness of the fault trees relatively to the system model. Hence, we introduce a novel method for the automatic verification of fault trees using the continuous real-time model-checker Uppaal [UUP05] for timed automata [AD94]. Therefore, fault trees with an DC semantics have to be transformed into timed automata, which can be verified by Uppaal. The connection to Uppaal, i.e. the generation of the timed automata and the appropriate requests, is automatically performed by Moby/FT.