Simulation-Based Dependability Analysis of Systems in Multiple Time-Horizons

When designing and operating any technical system, it is essential to take into account the possible faults that may occur during its operation. Dependability analysis lets us determine the level of redundancy that ensures continuity of service at an economically justified level of assurance. The analysis tends to underemphasize the extremely improbable, simultaneous failures of all or almost all system components. Yet, these situations should not be ignored as their consequences are often disastrous. The use of straightforward simulation in this case is very difficult-there is a huge disparity between the timescales of occurrence of the various types of events (connected with system functioning, fault occurrence and catastrophic breakdowns). The paper presents some experience with applying a unified simulation approach to deal with these multiple time-horizons. The usefulness of the proposed approach is demonstrated in two test studies: a discrete transport system and a web based information system.