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

The B method is known to be efficient, as a process of certifiable software implementation building in the domain of guided transports. There is important work to be performed using the informal specification before entering the B process. The upstream requirement analysis may be assisted with some graphical tools using UML notations. Nevertheless, the main problem to be solved may be the choice of the adequate tool. Currently, there are several kinds of diagrams in the UML notation and they are partially redundant. Considering a more general point of view, a main human contribution is to choose the representation which is specifically adapted to the considered assessment problem.

This paper introduces a methodology to analyze the safety of timed discrete event systems. Our case-study is the level crossing, a critical component for the safety of railway systems. First, our goal is to take out the forbidden state highlighted by a p-time Petri net modelling. This model deals with the requirements of the considered system and has to contain all the constraints that have to be respected. Then we describe a process identified as a solution for the system functioning. This method consists in exploring all the possible behaviors of the system by means of the construction of state classes. Finally, we check if the proposed process corresponds to the model of requirements previously built.

This paper presents a methodology to assist the safety assessment of timed discrete event systems. The methodology is illustrated on a level crossing case-study. It is a critical component for the safety of railway systems. The first step consists in decomposing the system functioning into different functioning modes. Then under specific assumptions, a model is provided for each functioning. Then, our goal is to take out the forbidden state highlighted by a p-time Petri net modelling. This model deals with the requirements of the considered system and has to contain all the constraints that have to be respected. Considering a proposed technological solution, its global functioning is also decomposed in several modes. As a latter, the model of the solution can be assessed, mode by mode. This assessment is achieved comparing the state classes deduced from the requirement model and the state classes of the proposed solution.

This paper aims at showing how it is possible to combine the advantages of highlevel Petri nets and the B method in order to design safety applications. In the railway critical software domain, safety requirements are obviously severe. Indeed, the passing from an informal specification to a formal one is a crucial point in critical software development. High-level Petri nets combine three important features: a graphical representation, a dynamic behaviour and an abstraction of the treatments. The B method allows one to pass from an abstract specification to a concrete implementation. We propose an approach that integrates the structuring and modelling of the system behaviour by means of coloured Petri nets from semi-formal specifications and the generation of a B abstract specification from this Petri net. Keywords: railway critical systems, safety, formal methods, model translation, high-level Petri nets, B method. 1 Introduction The technological progress of safety automation in railway systems involves a growing complexity of functional safety requirements. Thereby, this leads to the use of some technical tools for analysis and command synthesis that are more and more complex and efficient in order to respect the requirements. Moreover, the introduction of new European standards for railway safety has led one to reconsider critical system requirement specifications modelling.

Maximum staying time specifications often ensue from validity intervals and safety requirements. Therefore there is a need for modelling this kind of constraints. There are some studies in the state of the art dealing with train traffic modes with timed Petri net. Nevertheless, these kinds of results do not integrate the safety requirements we want to deal with. In this paper, we explain the reasons which lead us to use p-time Petri nets in order to model a well known case study: a level crossing benchmark. Level crossings are critical components of the European railway network. Nevertheless some accurate time specifications are used in order to fulfill some safety requirements. As the time specifications are difficult to deal with, this paper proposes to apply a dedicated modelling tool which can be found in the literature

The operational rules safety assessment of rail systems is a key element of the rail success to improve the competitiveness. In this context, the goal of this paper is to present a process for a safety analysis of operating rules. The first step of this process describes the operating rules and their formalisation using coloured Petri nets by means of a systematic method. The second step concerns the simulation of the resulting nets to check their properties. A group of ERTMS (European Rail Traffic Management System) operating rules, stemmed from HEROE (Harmonization of European rail Rules for Operating) project concerning the departure of a train will be used as an example. These rules are \“Departure”, \“Train preparation”, \“Permission of train movement authority” and \“Written orders”. Starting with a reminder of our systematic method of description based on coloured Petri nets (CPN), we show that the main advantage of this method is to standardize the rules description. Then, the properties of the resulting Petri nets are checked with appropriate tools, with a view to verifying liveness and to detecting possible deadlocks. Finally, we think that the process of formalisation and simulation will allow to check the consistency and the integrity of operating rules. 1 Introduction From the perspective to harmonize the European railway system, ERTMS (European Rail Traffic Management System) [1], which is the new European standard for train control systems, has been developed and must be implemented for upgrades of high-speed and conventional lines in accordance to the European Commission laws.

The goal of this paper is to show how it is possible to combine the advantages of Unified Modelling Language (UML) and of the B method in order to design safety applications. We investigate how the Unified Modeling Langage (UML), can be used to formally specify and verify critical railways systems. A benefit of using UML is it status as an international standard (OMG) and its widespread use in the software industry. B is a formal method for the incremental development of specifications and their refinements down to an implementation. In the railway critical software domain, safety requirements are obviously severe. It is very important to keep requirements traceability during software development process even if the different used models are informal, semi formal or formal. Keywords: B method, formal development, level crossing, software verification. 1 Introduction In spite of progress carried out in software development, designing a complex system while respecting its safety requirements, remains very hard. During the critical software development process, safety and security requirements must be traced from informal specification to code generation. So we need to trace them in the different models: informal, semi formal or formal ones. We present a new method here to transform a semi formal modelling to a formal specification which enables them to be traced. This method will be applied to a railways case study, where safety requirements are very strict. We study a level crossing case study taking into account French particularities. This article is made up 3 parts. Firstly, we describe the case study. In the following part we present the principles of UML and we give a part of semi formal modelling of the level crossing. In the last part