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Applicable Modelling, Verification and Analysis Techniques for Real-Time Systems (Ref. No. 1999/006), IEE Colloquium on

Date 11 Jan 1999

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Displaying Results 1 - 9 of 9
  • Using sharing trees in the automated analysis of real-time systems with data

    Page(s): 6/1 - 6/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    Reachability analysis and model checking of timed automata are now well-established techniques in the analysis of real-time control systems. The major limiting factor in their use, from a technical point of view, remains the state explosion problem. Symbolic representation of the state space often allows for the analysis of much larger systems than the point-wise representation which is common in enumerative analysis. In particular, the use of rooted, ordered binary decision diagrams (ROBDDs) has been successful, mainly in the analysis of hardware systems where the need for a compact representation of boolean functions is prevalent. However in software systems, it is often desirable to represent data types which are more complicated than booleans. The use of sharing trees, which eliminates the requirement to find a boolean encoding of all data types, may offer a more attractive alternative to ROBDDs in these circumstances. This paper considers the use of sharing trees in the context of automata derived from a timed algebra of asynchronous broadcasting systems. It suggests that an encoding of timing constraints may be more easily incorporated into a sharing tree representation of the state space than into one based on ROBDDs View full abstract»

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  • A modular tool for test generation for real-time systems

    Page(s): 3/1 - 3/4
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    A tool is presented which aims to meet the need for the automatic generation of test cases for real time control systems. The modular nature of the tool allows different specification languages to be used, and permits the user to experiment with a variety of simplifying transformations in order to produce a tractable model. Finally, a suitable test strategy can be selected. This flexibility allows the user to make the most appropriate selection of test cases, and at each stage the underlying assumptions are made explicit. Confidence in the implementation is expressed not as a percentage cover but as an explicit set of assumptions that are satisfied. It remains to investigate larger examples in order to establish the most effective techniques for reducing the number of test cases to a manageable size View full abstract»

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  • A framework for model-checking timed CSP

    Page(s): 5/1 - 5/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    Timed CSP is a well-known process algebra, built as an extension to Hoare's original CSP, designed to handle concurrency combined with timing considerations. It achieves this over a continuous time domain (the non-negative real numbers), which has the drawback of precluding standard model-checking approaches, as the state-space of any process is naturally a priori (uncountably) infinite. This paper shows how to circumvent this problem by translating and reinterpreting timed CSP processes within a new model of standard CSP. In this discrete model, which draws on previous work by A.W. Roscoe (1997) and A. Mukkaram (1993), timing of events is provided by the consistent and regular communication of a special tock event, analogous to the `tick' of a clock. The various parallel components of a process are therefore required to synchronise on tock, ensuring a uniform rate of passage of time. General results yielding tight bounds on the loss of information inherent to the translation are given View full abstract»

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  • Reducing conservatism in response time analysis of distributed systems

    Page(s): 7/1 - 7/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    Rate monotonic analysis (RMA) is a well-established technique for assessing schedulability of periodic and sporadic tasks which share a processor resource using fixed priority scheduling. An alternative approach to analysing such systems is to build a model which represents the behaviour of the system more dynamically, taking into account the dependency between the tasks View full abstract»

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  • Evolutionary algorithms for the verification of execution time bounds for real-time software

    Page(s): 8/1 - 8/8
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    Real-time systems must produce results according to a predefined time schedule. Therefore, their operation speed is critical. Timing analysis is crucial for the verification of a program's timing behaviour and an important part of design, testing and assessment. It measures how well a system matches its specifications. Static timing analysis concentrates on the evaluation of a program's internal structure to predict execution time bounds. But it does not consider a program's input parameters which are mainly responsible for the dynamic behaviour. Dynamic timing analysis can produce the most accurate assessment of run-time behaviour through the analysis of the interactions of a module's input parameters, but it is considered to be impractical because of the possible combinatorial explosion of the parameter combination space. However, powerful searching strategies such as evolutionary algorithms now make dynamic timing analysis of systems feasible. They only need to search through a fraction of the input parameters' total combination space and can be used to replace or supplement static techniques. Experiments with the new methodology have already shown significant improvement in the prediction of timing constraints, although the technique is merely in an experimental state View full abstract»

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  • UML and the formal development of safety-critical real-time systems

    Page(s): 2/1 - 2/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    The Unified Modeling Language (UML) is fast emerging as a de-facto standard for modelling object oriented systems. Like other software engineering methods, UML provides a set of graphical and textual modelling tools that aim to provide a common understandable language for developers and customers. However, UML has gone much further than previous methods in encouraging conformance of use. In particular, it provides a semantics document which aims to precisely describe the structure and meaning of the language. Recently, UML version 1.1 was accepted by the Object Management Group as a standard notation for object oriented analysis and design. Because of its growing popularity and the fact that it supports a number of real time facilities, there is a growing interest in applying UML to real time systems. Developers of safety-critical systems are also interested in UML because it claims to offer greater formality than other OO methods. There is hope that UML can provide a user friendly replacement for traditional formal notations. The article examines some of the issues associated with adopting UML for the development of safety-critical, real time systems. In particular we describe the current version of the language and its semantics (version 1.1) and explore its suitability as a basis for the formal specification of such systems. We then discuss some of the issues regarding formal refinement and deduction of UML models View full abstract»

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  • Specification-based testing for real-time avionic systems

    Page(s): 4/1 - 4/4
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    The paper describes the early stages of work towards the development of specification based testing techniques for real time distributed systems. This work has taken place in the context of the aerospace industry, where the complexity and the criticality of avionic systems makes them a challenge to develop. This paper briefly presents the DoRIs/ADL notation and its proof theoretic semantics, and sketches the techniques used to represent test cases for single activities. We look forward to the issues dominating future work on the automatic generation of tests from DoRIs/ADL models View full abstract»

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  • Method integration for real-time software design

    Page(s): 1/1 - 1/4
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    Although formal methods have been around for a number of years, their industrial take-up can be described at its best as poor. Some of the reasons have for this include: 1) problems in finding the right level of abstraction, 2) lack of user education, 3) hard to write a “good” specification, 4) difficult to understand, 5) absence of structure and method. Possible solutions could be: 1) create easier to use formal methods, 2) better education, 3) integrate formal methods with other methods (i.e. structured methods). The first has obviously been tried, judging from the amount of formal methods available. The second is of continuing focus in education establishments. The third is of most interest in the paper. Looking at structured design methods for real time software design, we note that they have had good take-up in industry, but generally lack the attributes that formal methods are specifically designed for. Structured methods have no rigorous definition of the structures that they employ, and little or no property verification facilities. The paper looks at integrating formal and structured methods for real time design and verification. More specifically we describe a case study integrating the diagrammatic formalism Modecharts and the structured design method HRT-HOOD, using the timed automata tool Uppaal for model checking properties of the HRT-HOOD design. One of the results of this approach is that the abstraction that the structured method brings, can be used to limit the state space when model checking a particular property, and so in many cases avoid the state space explosion View full abstract»

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