Philippe Bon’s research while affiliated with Gustave Eiffel University and other places

Relay-based Railway Interlocking Systems (RIS) are developed with the objective of controlling the movement of trains in a safe manner. However, these systems are generally specified by informal languages whose analyses are made by human inspection, which are error prone. A previous work presented an approach for specifying these systems in a formal language in order to automatically prove safety properties. Nevertheless, despite the impact of the environment over the system operation, the approach allows only the specification of the electrical components behaviour. Hence, the environment must be considered in the system specification in order to guarantee its safety. This paper presents the application of a higher level of modelling abstraction, conceptual modelling, which may provide a conceptual clarification of the RIS environment. This proposed conceptual model allows a semantic analysis of the environmental impact over the system and the description of other safety properties that have not been considered in the formal specification. In this work, an ontology built for the critical systems modelling is used in order to provide a terminological harmonisation between the physical elements of the system and the environment. The conceptual model allows a safety-oriented improvement of the RIS formal specification as well as it provides a common, shared and unambiguous view of both system and environment.

The safety assessment of Safety Critical Systems (SCSs) is a challenging task since it involves different actors and a combination of several knowledge domains. This increases the complexity of the integration of safety requirements into the design model. Consequently, there is a need for a shared model with an unambiguous terminology aiming to avoid misunderstandings between both safety and design teams. In this paper, we propose a model-based system engineering approach in order to support the goal-oriented safety reasoning and to provide a common model between both safety and requirement engineering driven by goals. Furthermore, the present study considers the safety rules development process based on the Organization-based Access Control (Or-BAC) model, which is normally used to improve the security of the information systems. Then, the common vocabulary proposed for the inter- pretation of the considered notions of domains is defined. Moreover, safety requirements are expressed with a high level of abstraction according to the required railway knowledge and the requirement trace- ability process is considered through an up-bottom reasoning using the Unified Modeling Language (UML) diagrams. The proposed approach aims to provide a methodology able to identify safety conditions in order to anticipate risks and to make better safety-related decisions. Finally, the proposed methodology is evaluated through a real accident scenario analysis in order to validate its adaptability to represent real critical situations.

Semantic interpretation of a knowledge domain is usually required to provide and formalize its common vocabulary. This task is challenging in the context of Safety Critical Systems (SCSs) development, since it involves both safety and design teams. In the railway domain, there is a lack of a common vocabulary aiming to avoid ambiguities in the safety-related decisions to satisfy goals. To cope with the complexity of this task, the aim of this study is to propose a semantic interpretation of the safety rules development process from a goal-oriented perspective. The safety rules development process is performed according to the Organization-Based Access Control (Or-BAC) model, which is normally used for the information systems security. The proposed approach is based on a foundational ontology in order to interpret safety-related concepts in real-world semantics. It provides relations between safety-related concepts and Unified Foundational Ontology (UFO) concepts. Furthermore, the matching between safety rules, Or-BAC and Goal-Oriented Requirements Engineering (GORE) concepts is considered and formalized in a structured way. The proposed interpretation is evaluated and progressively justified regarding the railway domain knowledge and the current literature.

The verification of safety properties of critical systems, such as railway signaling systems, is better achieved by formal reasoning. Event-B as a formal method, allows to get safe and reliable systems. Nevertheless, modeling with Event-B method requires some knowledge on mathematical logic and set theory. In opposition, UML (Unified Modeling Language) is a commonly used graphical language, but it does not guarantee the verification of safety properties. This paper presents an approach combining UML and Event-B. In fact, we focus in this work on modeling the systems behavior with the joint use of some UML behavioral diagrams. The UML models are then translated into Event-B models for the systems validation as well as the verification of safety properties using B tools. This methodology is illustrated by an application on a case study of railway signaling system.

A railway interlocking system is one example of a critical system, and, therefore, it must have a high level of reliability in order to avoid problems that may result on the loss of people's lives. However, many railway systems are still specified using historical relay-based diagrams, whose analysis are made by human inspection, which is error prone. Relay-based diagrams are specified by nodes and cables in a graphical manner, which resemble undirected graphs. This paper presents a framework for the specification of relay diagrams in a formal language, B-method, based on the specification of a graph and its properties. The use of a formal language allows one to prove the correctness of these railway interlocking systems regarding structural properties. This framework has been evaluated by the specification of a case study.