Lobianco, Wanderley Júnior; (1994) Structuring Diversely Designed Software. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

There are a number of computer control systems in which a fault in the software can endanger human lives or lead to substantial financial loss. Software fault-tolerance provides tolerance to residual design faults in the software by means of diversely designed versions which comply with a single specification. This has proved to be an effective way of increasing software reliability. However, there are designers who hesitate to adopt this approach because of the additional cost of producing and integrating diversely designed software and assessment algorithms. Hence, guidelines are needed for structuring fault-tolerant software so that the time and cost of developing and integrating multiple versions and assessment components are reduced. The main contribution of this research is to propose and justify a framework for structuring fault-tolerant software based on reusable components that encapsulate data and communicate by message exchange via indirect addressing. Reusable components allow for a reduction in the cost of system development, as fewer specially tailored modules are needed. Moreover, the reliability of reusable components have been observed in the field. The framework provides a transparent filter between the diversely designed versions and the modules that communicate with them. Therefore, fault-tolerant software modules are interchangeable with functionally equivalent components that do not tolerate residual design faults. As a result, software components do not need to have special interfaces either to communicate with fault-tolerant modules or to be configured as diversely designed versions. The framework caters for the realisation of fault-tolerant modules based on well-known software fault-tolerance techniques, such as: compensation, exception handling, recovery blocks, and n-version programming. In addition, it extends their applicability by providing a structured way of combining them.

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