Abstract
Assessment of software reliability is an area of the utmost importance for software-based systems employed in safety-critical applications such as computer relaying of power transmission lines. In a typical software development process, software is designed as a combination of components and modules instead of a monolithic block. Different components contribute to varying degrees to the overall functioning of software and thus knowledge of component importance can reveal vital information for software designers and test engineers. Moreover, software reliability is estimated on the basis of collected historical data followed by an assumed distribution curve and is thus inherently susceptible to uncertainties. The fault tree is an important aid that is used widely for safety and reliability consideration of component-based systems and can also be applied to software. In fault tree analysis, the uncertainties in the failure probability of a system's basic component can be propagated to find the uncertainty of the overall system. Fuzzy set theory has been used in fault tree analysis for quantifying the basic event uncertainty and for propagating it. In this paper, a methodology to assess fuzzy module importance as well as fuzzy module uncertainty importance of software has been presented. A case study of computer relay software has been used to demonstrate the viability of the proposed methodology.
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