IESM 2015 - International Conference on Industrial Engineering and Systems, Séville, ESPAGNE, 21-/10/2015 - 23/10/2015Reaching the critical software safety requirements is one of the most important and complex tasks for the safety-related industry. This fact explains, as it was highly recommended by the CENELEC standard, the increasing use of formal means in the development process. However, industrial environments are still reticent facing difficulties in incorporating those formal methods in a larger scale of application, especially because of their mathematical modeling complexity. The present paper proposes a Petri Nets-based approach for safety critical software development using a formal transformation into B abstract machines. This work presents formal definitions for the translation of Colored Petri Nets to B abstract machines. As part of the French research project called 'PERFECT', it aims at enabling a stronger combination of formal design techniques and analysis tools in order to cope with the real complexity of critical software development and to prove in an automated manner that the final software product satisfies all safety requirements. Therefore, the use of the B method will broaden the scope of its applicability by providing a new input modeling alternative. An illustrative application of the transformation practical use is shown in this paper for a railway level-crossing case study

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Verification methods can be classified according to two kinds of criteria: static or not -i.e. dynamic -and formal or not. This paper follows a work about verification of temporal properties using dynamic analysis. The approach proposes to transform an LTL property into a Büchi automaton and to run the automaton on an execution trace to be verified. Because traces are finite, the end of trace problem can be bypassed with computation of statistical information about the verified trace if and only if the property follows a predefined given pattern. For very big traces, this approach is well-adapted, but traces have to be sequentially verified. This paper proposes to parallelize the verification approach by splitting the execution trace and executing the Büchi automaton on each sub-trace separately analysable, which allows a significant time saving.

Dysfunctional analysis is an essential and demanding task in the early development stages of safety-critical systems (SCSs). Nevertheless, current practices present several drawbacks. Generally, a common dysfunctional analysis conceptualization is missing and it is dependent on safety analysis techniques. Moreover, some safety analysis methods require well-known system behaviors expressed by dynamic models such as sequence diagrams and finite automata. However, the dynamic character of these models increases their susceptibility to changes and then they are not obtainable in the early design stages. Since dysfunctional analysis highly relies on the experience of safety analysts and the feedback (REX) obtained from previous systems development, there is a need to formalize this knowledge domain in a structured way to ensure its future reuse. Furthermore, safety measures derived from this dysfunctional analysis approach must be strongly linked to a goal-oriented perspective and adapted to a specific context. For this purpose, this paper presents a real-world semantics interpretation and conceptualization of dysfunctional analysis related concepts based on the Unified Foundational Ontology (UFO) and well-known standards to avoid ambiguities. The proposed Dysfunctional Analysis Ontology (DAO) aims to provide a systematization of the goal-oriented dysfunctional analysis through a terminological clarification in order to prevent hazards in the first design phases. Then, a DAO formalization is proposed using the Web Ontology Language (OWL). Finally, the DAO pattern is applied to two different real critical scenarios from the railway domain in order to illustrate and evaluate this ontological approach.

In order to cope with the increasing design complexity of safety-critical systems, safety assurance should be considered as early as possible in the design process. Using Model-Based System Engineering (MBSE) approaches however lead to new challenges regarding the cohesive integration of both safety engineering and system design along the system development process. Moreover, it helps to anticipate safety problems and detect errors as soon as possible. This is the case of railway systems, which are complex socio-technical systems. From this point of view, the purpose of the present study is to formalize a safety reasoning based on the definition of critical scenarios. The objective is to propose a proactive approach that takes these requirements into account early in the system architecture design. By identifying the impact on the design of the architecture, we will ensure safety by integrating technical devices and human interventions. Based on the related literature, the Preliminary Risk Analysis (PRA) is attested to define safety conditions. These safety requirements are expressed with a high level of abstraction according to the level of knowledge engineering. Qualitative risk analysis methods, such as Fault Tree Analysis (FTA) will be used to analyze the propagation of failures. The second challenge is to trace the high level requirements during the design steps. In order to help the designer to consider safety aspect in the system architecture synthesis, we integrate safety concerns from early design stages, within the MBSE approach. In this paper, we propose a methodology to effectively identify safety conditions, thus to anticipate risks. We also focus our work on the European Railway Traffic Management System (ERTMS). Finally, we applied specific transformation rules on our ERTMS ontology in order to build a Unified Modeling Language (UML) model.