This thesis describes a methodology for the requirements analysis of critical real-time systems. The methodology is based on formal methods, and provides a systematic way in which requirements can be analysed and specifications produced. The proposed methodology consists of a framework with distinct phases of analysis, a set oftechniques appropriate for the issues to be analysed at each phase of the framework, a hierarchical structure of the specifications obtained from the process of analysis, and techniques to perform quality assessment of the specifications. The phases of the framework, which are abstraction levels for the analysis of the requirements, follow directly from a general structure adopted for critical real-time systems. The intention is to define abstraction levels, or domains, in which the analysis of requirements can be performed in terms of specific properties of the system, thus reducing the inherent complexity of the analysis. Depending on the issues to be analysed in each domain, the choice of the appropriate formalism is determined by the set of features, related to that domain, that a formalism should possess. In this work, instead of proposing new formalisms we concentrate on identifying and enumerating those features that a formalism should have. The specifications produced at each phase of the framework are organised by means of a specification hierarchy, which facilitates our assessment of the quality of the requirements specifications, and their traceability. Such an assessment should be performed by qualitative and quantitative means in order to obtain high confidence (assurance) that the level of safety is acceptable. In order to exemplify the proposed methodology for the requirements analysis of critical real-time systems we discuss a case study based on a crossing of two rail tracks (in a model railway), which raises safety issues that are similar to those found at a traditional level crossing (i.e. rail-road).

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Embedded systems exists everywhere around us and the number of applications seems to be ever growing. They are found in electrical devices from coee machines to aircrafts. The common denominator is that they are designed for the specic purpose of the application. Some of them are used in safety critical systems where it is crucial that they operate correct and as intended in order to avoid accidents that can harm humans or properties. Meanwhile, general purpose Commercial O The Shelf (COTS) devices that can be found in the retail store, such as smartphones and tablets, has become a natural part of everyday life in the society. New applications are developed every day that improves everyday living, but numerous are also coupled to specic devices in order to control its functionality. Interaction between embedded systems and the exible devices do however not come without issues. Security, safety and ethical aspects are some of the issues that should be considered. In this thesis, a case study was performed to investigate the feasibility of using mobile COTS products in interaction with safety critical systems with respect to functional safety. Six user scenarios were identied for investigation, which could be of interest for industrial applications; The operator presented live machine data, The operator controlling the machine remotely, The service technician using mobile device in maintenance, service technician reading machine logs from the oce, the production manager analyzing machine productivity logs from the oce and the software manager uploading software. Restrictions in the functional safety standard, IEC 61508, and the characteristics of COTS devices, leads to the conclusion that real time interaction with safety systems is not allowed if the certication is to be preserved. Extracting information used to analyze the system where data is only sent from the machine would be allowed. All scenarios where the machine sends data to the user, and the data is only used as information, are hence allowed if isolation properties are guaranteed. A prototype system was designed and parts of it were implemented to show how sending and logging information can be performed using the company developed communication platform Data Engine.

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Software product line engineering is a proposed methodology that enables software products and software-intensive systems to be developed at lower cost, higher quality and less time to market. The structured and managed artifacts reuse among different products in development is the main target of software product line engineering. As a key-method of the product line engineering approach, the commonality and variability analysis is a technique that identifies the potential artifacts for reuse. But the reuse poses challenges for delivering safety-critical products from the product line and achieving product line functional safety. In order to analyze the product line and provide more valuable information for its safety analysis, we make use of established product line modeling techniques, which model the product line commonality and variability from different perspectives. In this report, we investigate the product line modeling techniques. The product modeling analysis process covers two aspects: 1. Study different product line modeling techniques and find the ones suitable for product line modeling. We choose the modeling techniques that can be implemented to discuss in detail. 2. We implement the industrial wheel loader product line with two modeling techniques. Comprehensive models and detailed modeling process explanation are presented. The product line functional safety analysis covers three aspects: 1. Investigate the different safety analysis techniques and choose the fault tree analysis as the main technique. 2. Extend the single system fault tree to the product line fault tree. 3. Investigate the contributions of the product line modeling techniques to the product line functional safety analysis. Specifically, we map the product line models to the product line fault tree. Furthermore, we evaluate the product line modeling techniques from their performance in domain analysis and safety analysis.