Formalization and Validation of Safety-Critical Requirements

The validation of requirements is a fundamental step in the development process of safety-critical systems. In safety critical applications such as aerospace, avionics and railways, the use of formal methods is of paramount importance both for requirements and for design validation. Nevertheless, while for the verification of the design, many formal techniques have been conceived and applied, the research on formal methods for requirements validation is not yet mature. The main obstacles are that, on the one hand, the correctness of requirements is not formally defined; on the other hand that the formalization and the validation of the requirements usually demands a strong involvement of domain experts. We report on a methodology and a series of techniques that we developed for the formalization and validation of high-level requirements for safety-critical applications. The main ingredients are a very expressive formal language and automatic satisfiability procedures. The language combines first-order, temporal, and hybrid logic. The satisfiability procedures are based on model checking and satisfiability modulo theory. We applied this technology within an industrial project to the validation of railways requirements

Verifying service continuity in a satellite reconfiguration procedure: application to a satellite

The paper discusses the use of the TURTLE UML profile to model and verify service continuity during dynamic reconfiguration of embedded software, and space-based telecommunication software in particular. TURTLE extends UML class diagrams with composition operators, and activity diagrams with temporal operators. Translating TURTLE to the formal description technique RT-LOTOS gives the profile a formal semantics and makes it possible to reuse verification techniques implemented by the RTL, the RT-LOTOS toolkit developed at LAAS-CNRS. The paper proposes a modeling and formal validation methodology based on TURTLE and RTL, and discusses its application to a payload software application in charge of an embedded packet switch. The paper demonstrates the benefits of using TURTLE to prove service continuity for dynamic reconfiguration of embedded software

The specification-based validation of reliable multicast protocol: Problem Report

Reliable Multicast Protocol (RMP) is a communication protocol that provides an atomic, totally ordered, reliable multicast service on top of unreliable IP multicasting. In this report, we develop formal models for RMP using existing automated verification systems, and perform validation on the formal RMP specifications. The validation analysis help identifies some minor specification and design problems. We also use the formal models of RMP to generate a test suite for conformance testing of the implementation. Throughout the process of RMP development, we follow an iterative, interactive approach that emphasizes concurrent and parallel progress of implementation and verification processes. Through this approach, we incorporate formal techniques into our development process, promote a common understanding for the protocol, increase the reliability of our software, and maintain high fidelity between the specifications of RMP and its implementation

Early Requirements Validation with 3D Worlds

It is a well-known fact the real significance of correctly determining requirements of a system at the very beginning of the development process. Indeed, experience demonstrates that the incorrect definition of requirements leads to development of deficient systems, increases the cost of its development or even causes projects to fail. Thus, it is crucial for clients to verify that the planned system satisfies their needs. In order to help users in the process of requirements understanding and validation this work proposes using 3D visualization techniques. The use of these techniques can reduce the communication gap between clients and developers resulting in a much more effective process of requirements validation. The approach tries to take advantage of the benefits of the 3D visualization, complementing this with the advantages of formal specifications. The approach proposes the use of formal specifications in a lighter way. This means that no formal reasoning (theorem proving) is carried out to check the properties of the specified system and the emphasis is focused on the execution and animation of the specification for early validation. A prototype tool that materializes the proposal was developed. The tool allows specifying the requirements in the formal language Z, defining a graphical representation of them and creating a 3D animated visualization of their execution through which the users can validate them.Fil: Teyseyre, Alfredo Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Instituto Superior de Ingeniería del Software. Universidad Nacional del Centro de la Provincia de Buenos Aires. Instituto Superior de Ingeniería del Software; ArgentinaFil: Campo, Marcelo Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Instituto Superior de Ingeniería del Software. Universidad Nacional del Centro de la Provincia de Buenos Aires. Instituto Superior de Ingeniería del Software; Argentin

Towards validated real-time software

We present a tool for the design and validation of embedded real time applications. The tool integrates two approaches: the use of the synchronous programming language, ESTEREL for design, and the application of model checking techniques for validation of real time properties. Validation is carried out on a global formal model (timed automata) taking into account the effective implementation of the application on the target hardware architecture as well as its external environment behavio

Fuzzy Logic Controller Stability Analysis Using a Satisfiability Modulo Theories Approach

While many widely accepted methods and techniques exist for validation and verification of traditional controllers, at this time no solutions have been accepted for Fuzzy Logic Controllers (FLCs). Due to the highly nonlinear nature of such systems, and the fact that developing a valid FLC does not require a mathematical model of the system, it is quite difficult to use conventional techniques to prove controller stability. Since safety-critical systems must be tested and verified to work as expected for all possible circumstances, the fact that FLC controllers cannot be tested to achieve such requirements poses limitations on the applications for such technology. Therefore, alternative methods for verification and validation of FLCs needs to be explored. In this study, a novel approach using formal verification methods to ensure the stability of a FLC is proposed. Main research challenges include specification of requirements for a complex system, conversion of a traditional FLC to a piecewise polynomial representation, and using a formal verification tool in a nonlinear solution space. Using the proposed architecture, the Fuzzy Logic Controller was found to always generate negative feedback, but inconclusive for Lyapunov stability

A Comparative Analysis To Validate The Benefits Of Formal Versus Informal Software Model Transformation

In object -oriented development the Unified Modeling Language (UML) is the ISO/IEC standard for modeling language and is supported by major corporations. In relational database development, entity-relationship models have traditionally been use for modeling such systems. Transforming from one notation to another notation is of great importance in developmental environments where this is required. There are several techniques for transforming UML models to object-relational database systems. Prior assessment has been carried out on transforming UML class diagram models to object-oriented relational databases, which yield significant results. One approach to transformation may involve the use of formal (mathematical) techniques, while other approaches may rely on informal techniques to accomplish the transformation. The use of a formal technique to transform may incorporate graph-theory on UML class diagram. An informal technique may be utilized in transforming UML extension mechanisms, to represent object-relational concepts. A prior research effort examined the benefits of two such approaches in transforming UML class diagram models into object-relational database representation. That work, sought to determine the benefits of one approach (formal technique) versus the benefits of the other approach (informal technique), by way of comparative analysis. The researchers drew inferences from the comparative analysis as to the suitability of one approach versus the other on classes of problem domains. The results of such work have to be validated in order for it to become acceptable and its implication applied in software development decision making. In this work there will be an attempt to apply a similar xiv comparative analysis on a model from a different application domain (Kalman Filter Program Representation), from that which was used in the first study an (Airline Flight Reservation System). The goal of this research is to provide validation of the usefulness of this type of comparative analysis

Formalization and Model Checking of BPMN Collaboration Diagrams with DD-LOTOS

Business Process Model and Notation (BPMN) is a standard graphical notation for modeling complex business processes. Given the importance of business processes, the modeling analysis and validation stage for BPMN is essential. In recent years, BPMN notation has become a widespread practice in business process modeling because of these intuitive diagrams. BPMN diagrams are built from basic elements. The major challenge of BPMN diagrams is the lack of formal semantics, which leads to several interpretations of the concerned diagrams. Hence, this work aims to propose an approach for checking BPMN collaboration diagrams to guarantee some properties of smooth functioning of systems modeled by BPMN notation. The verification approach used in this work is based on model checking techniques. The approach proposes as a first step a formal semantics of the collaboration diagrams in terms of the formal language DD-LOTOS, i.e., a phase of the transformation of collaboration diagrams into DD-LOTOS. This transformation is guided by applying the inference rules of the formal semantics of the DD-LOTOS formal language, and we then use the UPPAAL model checker to check the absence of deadlock, safety properties, and liveness properties

Classification Criteria for Sympathetic Ophthalmia

PURPOSE: To determine classification criteria for sympathetic ophthalmia DESIGN: Machine learning of cases with sympathetic ophthalmia and 5 other panuveitides. METHODS: Cases of panuveitides were collected in an informatics-designed preliminary database, and a final database was constructed of cases achieving supermajority agreement on the diagnosis, using formal consensus techniques. Cases were split into a training set and a validation set. Machine learning using multinomial logistic regression was used on the training set to determine a parsimonious set of criteria that minimized the misclassification rate among the panuveitides. The resulting criteria were evaluated on the validation set. RESULTS: One thousand twelve cases of panuveitides, including 110 cases of sympathetic ophthalmia, were evaluated by machine learning. The overall accuracy for panuveitides was 96.3% in the training set and 94.0% in the validation set (95% confidence interval 89.0, 96.8). Key criteria for sympathetic ophthalmia included bilateral uveitis with 1) a history of unilateral ocular trauma or surgery and 2) an anterior chamber and vitreous inflammation or a panuveitis with choroidal involvement. The misclassification rates for sympathetic ophthalmia were 4.2 % in the training set and 6.7% in the validation set, respectively. CONCLUSIONS: The criteria for sympathetic ophthalmia had a low misclassification rate and appeared to perform sufficiently well for use in clinical and translational research