ISBN : 978-81-963532-2-3 (E-Book) • theresourcesavailable tothemaintenanceteam • theconditionsof theexistingproduct(e.g., howstructuredit is,how well documenteditis, etc.) • theexpectedprojectrisks,etc. When the changes needed to a software product are minor and straightforward, the code can bedirectlymodifiedandthechangesappropriatelyreflectedinallthedocuments.Butmoreelaborateacti vitiesarerequiredwhentherequiredchangesarenotsotrivial.Usually,forcomplex maintenance projects for legacy systems, the software process can be represented by areverse engineering cycle followed by a forward engineering cycle with an emphasis on as muchreuseas possiblefrom the existingcodeand otherdocuments. RELIABILITYGROWTHMODELS A reliability growth modelisa mathematicalmodelof how software reliability improvesaserrors are detected and repaired. A reliability growth model can be used to predict when (or if atall) a particular level of reliability is likely to be attained. Thus, reliability growth modeling canbe used to determine when to stop testing to attain a given reliability level. Although severaldifferent reliability growth models have been proposed, in this text we will discuss only two verysimplereliabilitygrowthmodels. Jelinski and Moranda Model -The simplest reliability growth model is a step function modelwhere it is assumed that the reliability increases by a constant increment each time an error isdetected and repaired. Such a model is shown in fig. 27.1. However, this simple model ofreliability which implicitly assumes that all errors contribute equally to reliability growth, ishighly unrealistic since it is already known that correction of different types of errors contributedifferentlyto reliabilitygrowth. 113 Software Engineering Keerthana P, Manasa KN, Ganga D Bengal
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