Analysis of an Inflection S-shaped Software Reliability Model Considering Log-logistic Testing-Effort and Imperfect Debugging

Gokhale and Trivedi (1998) have proposed the Log-logistic software reliability growth model that can capture the increasing/ decreasing nature of the failure occurrence rate per fault. In this paper, we will first show that a Log-logistic testing-effort function (TEF) can be expressed as a software development/testing-effort expenditure curve. We investigate how to incorporate the Log-logistic TEF into inflection S-shaped software reliability growth models based on non-homogeneous Poisson process (NHPP). The models parameters are estimated by least square estimation (LSE) and maximum likelihood estimation (MLE) methods. The methods of data analysis and comparison criteria are presented. The experimental results from actual data applications show good fit. A comparative analysis to evaluate the effectiveness for the proposed model and other existing models are also performed. Results show that the proposed models can give fairly better predictions. Therefore, the Log-logistic TEF is suitable for incorporating into inflection S-shaped NHPP growth models. In addition, the proposed models are discussed under imperfect debugging environment.