Abstract. This paper describes the XSAP safety analysis platform. XSAP provides several model-based safety analysis features for finite-and infinite-state synchronous transition systems. In particular, it supports library-based definition of fault modes, an automatic model extension facility, generation of safety analysis artifacts such as Dynamic Fault Trees (DFTs) and Failure Mode and Effects Analysis (FMEA) tables. Moreover, it supports probabilistic evaluation of Fault Trees, failure propagation analysis using Timed Failure Propagation Graphs (TFPGs), and Common Cause Analysis (CCA). XSAP has been used in several industrial projects as verification back-end, and is currently being evaluated in a joint R&D Project involving FBK and The Boeing Company.
Many possible solutions, differing in the assumptions and implementations of the components in use, are usually in competition during early design stages. Deciding which solution to adopt requires considering several trade-offs. Model checking represents a possible way of comparing such designs, however, when the number of designs is large, building and validating so many models may be intractable. During our collaboration with NASA, we faced the challenge of considering a design space with more than 20,000 designs for the NextGen air traffic control system. To deal with this problem, we introduce a compositional, modular, parameterized approach combining model checking with contract-based design to automatically generate large numbers of models from a possible set of components and their implementations. Our approach is fully automated, enabling the generation and validation of all target designs. The 1,620 designs that were most relevant to NASA were analyzed exhaustively. To deal with the massive amount of data generated, we apply novel data-analysis techniques that enable a rich comparison of the designs, including safety aspects. Our results were validated by NASA system designers, and helped to identify novel as well as known problematic configurations.
Automated detection of faults and timely recovery are fundamental features for autonomous critical systems. Fault Detection and Identification (FDI) components are designed to detect faults on-board, by reading data from sensors and triggering predefined alarms. The design of effective FDI components is an extremely hard problem, also due to the lack of a complete theoretical foundation, and of precise specification and validation techniques. In this paper, we present the first formal framework for the design of FDI for discrete event systems. We propose a logical language for the specification of FDI requirements that accounts for a wide class of practical requirements, including novel aspects such as maximality and nondiagnosability. The language is equipped with a clear semantics based on temporal epistemic logic. We discuss how to validate the requirements and how to verify that a given FDI component satisfies them. Finally, we develop an algorithm for the synthesis of correct-by-construction FDI components, and report on the applicability of the framework on an industrial case-study coming from aerospace.
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