Using z specification for railway interlocking safety (original) (raw)
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Towards the formalization of railway interlocking system using Z-notations
… , Control and Communication, 2009
Railway interlocking system is a safety critical system. Its malfunction can cause the loss of human life and severe injuries. To remove difficulties from this type of system better and advanced methodologies are required. This paper presents the use of Z-specification to specify the safety properties of the train system. The paper provides division of railway track into sectors and further division into segments. For the safety of the train a safe distance (open block) is associated with trains to avoid collision. Furthermore, this work uses the circular block around the crossing region. The circular block changes its state from green to red whenever it becomes occupied. Moreover the paper also specifies the safety of trains along the linear motion. This work uses the approach of promotion, which provides relation from local to global system. The authors take train as local system and relate it to the whole system through the operation of promotion. The paper also shows how formal methods are used to specify industrial application successfully.
Pollack Periodica, 2019
The use of formal modeling has seen an increasing interest in the development of safety-critical, embedded microcomputer-controlled railway interlocking systems, due to its ability to specify the behavior of the systems using mathematically precise rules. The research goal is to prepare a specification-verification environment, which supports the developer of the railway interlocking systems in the creation of a formally-proven correct design and at the same time hides the inherent mathematical-computer since related background knowledge. The case study is presented with the aim to summarize the process of formalizing a domain specification, and to show further application possibilities (e.g. verification methods).
Integrating Automatic Verification of Safety Requirements in Railway Interlocking System Design
2001
A railway interlocking system (RIS) is an embedded system (namely a supervisory control system) that ensures the safe, operation of the devices in a railway station. RIS is a safety critical system. We explore the possibility of integrating automatic formal verification methods in a given industry RIS design flow. The main obstructions to be overcome in our work are: selecting a formal verification tool that is efficient enough to solve the verification problems at hand; and devising a cost effective integration strategy for such tool. We were able to devise a successful integration strategy meeting the above constraints without requiring major modification in the pre-existent design flow nor retraining of personnel. We run verification experiments for a RIS designed for the Singapore Subway. The experiments show that the RIS design flow obtained from our integration strategy is able to automatically verify real life RIS designs
A Model-Based Approach to the Design, Verification and Deployment of Railway Interlocking System
2020
This paper describes a model-based flow for the development of Interlocking Systems. The flow starts from a set of specifications in Controlled Natural Language (CNL), that are close to the jargon adopted in by domain experts, but fully formal. From the CNL, a complete SysML specification is extracted, leveraging various forms of diagrams, and enabling automated code generation. Several formal verification methods are supported. A complementary part of the flow supports the extraction of formal properties from legacy Interlocking Systems designed as Relay circuits. The flow is implemented in a comprehensive toolset, and is currently used by railway experts.
2008
In this project the verification of safety conditions for the control of a railway interlocking system written in ladder logic is carried out. All translation steps have been implemented and tested for a real-world example of a railway interlocking system. The steps in this translation are as follows: 1. The development of a mathematical model of a railway interlocking system and the translation from ladder logic into this model. 2. The development of verification conditions guaranteeing the correctness of safety conditions. 3. The verification of safety conditions using a SAT solver. 4. The generation of specific safety conditions from more generic ones using a topological model of a railway yard.
Formal verification of a railway interlocking system using model checking
1998
In this paper we describe an industrial application of formal methods. We have used model checking techniques to model and formally verify a rather complex software, i.e. part of the "safety logic" of a railway interlocking system. The formal model is structured to retain the reusability and scalability properties of the system being modelled. Part of it is defined once for all at a low cost, and re-used. The rest of the model can be mechanically generated from the designers' current specification language. The model checker is "hidden" to the user, it runs as a powerful debugger. Its performances are impressive: exhaustive analysis of quite complex configurations with respect to rather complex properties are run in the order of minutes. The main reason for this achievement is essentially a carefully designed model, which exploits all the behaviour evolution constraints. The re-usability/scalability of the model and the fact that formal verification is automatic and efficient are the key factors which open up the possibility of a real usage by designers at design time. We have thus assessed the possibility of introducing the novel technique in the development cycle with an advantageous costs/benefits relation.
Model checking railway interlocking systems
Australian Computer Science Communications, 2002
For supporting the analysis of railway interlocking systems in the early stage of their design we propose the use of model checking. We investigate the use of the formal modelling language CSP and the corresponding model checker FDR. In this paper, we describe the basics of this formalism and introduce our formal model of a railway interlocking system. Checking this model against the given safety requirements, the signalling principles, we get useful counterexamples that help to debug the given interlocking design. This work provides a successful example of how formal methods can be used to support the industrial development process.
Validation process for railway interlocking systems
Science of Computer Programming, 2016
An interlocking system monitors the status of the objects in a railway yard, allowing or denying the movement of trains, in accordance with safety rules. The high number of complex interlocking rules that guarantee the safe movements of independent trains in a large station makes the verification of such systems a complex task, which needs to be addressed in conformance with EN50128 safety guidelines. In this paper we show how the problem has been addressed by a manufacturer at the final validation stage of production interlocking systems, by means of a model extraction procedure that creates a model of the internal behaviour, to be exercised with the planned test suites, in order to reduce the high costs of direct validation of the target system. The same extracted model is then subject to formal verification experiments, employing an iterative verification process implementing slicing and CEGAR-like techniques, defined to address the typical complexity of this application domain.
A formal verification environment for railway signaling system design
Formal Methods in …, 1998
A fundamental problem in the design and development of embedded control systems is the verification of safety requirements. Formal methods, offering a mathematical way to specify and analyze the behavior of a system, together with the related support tools can successfully be applied in the formal proof that a system is safe. However, the complexity of real systems is such that automated tools often fail to formally validate such systems.