SAFETY ANALYSIS OF SYSTEMS (original) (raw)

Validating Formal Verification using Safety Analysis Techniques

1999

The increased interest in the use of automated safety analysis is supported by the claim that manual safety analysis based on traditional techniques is error-prone, costly and not necessarily complete. It is also claimed that traditional techniques are not able to deal with the inherent complexities of software intensive systems. However, we show in this paper that a transition (from manual to automatic approaches) in the assessment process and technologies is accompanied by an inherent risk of obtaining false confidence, unless safeguards are provided. The safeguard presented in this paper integrates traditional deductive and inductive analysis techniques with model checking, a form of formal verification. The aim is to provide the safety analyst with a rigourous approach for the validation of formal models. The feasibility of the overall approach is illustrated in terms of a case study.

Model checking of safety properties

2001

Of special interest in formal verification are safety properties, which assert that the system always stays within some allowed region. Proof rules for the verification of safety properties have been developed in the proof-based approach to verification, making verification of safety properties simpler than verification of general properties. In this paper we consider model checking of safety properties. A computation that violates a general linear property reaches a bad cycle, which witnesses the violation of the property.

Integration of Formal Methods into System Safety and Reliability Analysis

1999

System verification and hazard analysis procedures on critical systems are traditionally carried out in separate stages of product development and by different teams of engineers. Safety and hazard analyses have for several decades been based on techniques such as fault tree analysis (FTA), whereas system verification is carried out by testing and simulation. Recent years have seen an increasing interest in application of formal methods for detecting design errors at early development stages. In this paper we propose a technique whereby both safety correctness proofs and reliability analysis, like FTA, can be performed on one design model: a model of the system in propositional logic and integer arithmetic. An obvious benefit is that the two parallel activities take place in the development process in a natural manner, and using a common model. The model is used for performing FTA-like analysis without building the fault-tree. We describe the application with examples from the aeros...

Extending Safety Analysis Techniques with Formal Semantics

Technology and Assessment of Safety-Critical Systems, 1994

Among the causes of many of the problems with safety analysis are impreciseness and ambiguity of the output data delivered by the safety analysis techniques and the resulting difficulties with interpretation of those data. An approach which can be undertaken to mitigate this problem is by providing the safety analysis techniques with more formal semantics. This paper aims to investigate this approach in more detail. First we give an overview of present practices during safety analysis. Then some problems with interpretation of the output from the presented methods are identified. This leads to the motivation to resolve ambiguities by adding more formality to the considered methods. The benefits of such approach are demonstrated by applying the formalism to some examples.

Safety-Critical Systems, Formal Methods and Standards

Software Engineering Journal, 1993

Standards concerned with the development of safety-critical systems, and the software in such systems in particular, abound today as the software crisis increasingly affects the world of embedded computer-based systems. The use of formal methods is often advocated as a way of increasing confidence in such systems. This paper examines the industrial use of these techniques, the recommendations concerning formal methods in a number of current and draft standards, and comments on the applicability and problems of using formal methods for the development of safety-critical systems of an industrial scale. Some possible future directions are suggested. Winner of the IEE Charles Babbage Premium award, 1994. Other versions issued as a Oxford University Computing Laboratory Technical Report PRG-TR-5-92, and Chapter 1 in Towards Verified Systems.

The practice of formal methods in safety-critical systems

Journal of Systems and Software, 1995

By describing several industrial-scale applications of formal methods, this paper intends to demonstrate that formal methods for software development and safety analysis are increasingly adopted in the safety critical systems sector. The benets and limitations of using formal methods are described, and the problems of developing software for safety critical systems are analysed.

Practical Application of Functional and Relational Methods for the Specification and Verification of Safety Critical Software

Proceedings of Algebraic Methodology and Software Technology, 8th International Conference, AMAST 2000, 2000

In this paper we describe how a functional version of the 4-variable model can be decomposed to improve its practical application to industrial software verification problems. An example is then used to illustrate the limitations of the functional model and motivate a modest extension of the 4-variable model to an 8-variable relational model. The 8-variable model is designed to allow the system requirements to be specified as functions with input and output tolerance relations, as is typically done in practice. The goal is to create a relational method of specification and verification that models engineering intuition and hence is easy to use and understand.