An Evaluation Model for Dependability of Internet-scale Software on Basis of Bayesian Networks and Trustworthiness

Internet-scale software becomes more and more important as a mode to construct software systems when Internet is developing rapidly. Internet-scale software comprises a set of widely distributed software entities which are running in open, dynamic and uncontrollable Internet environment. There are several aspects impacting dependability of Internet-scale software, such as technical, organizational, decisional and human aspects. It is very important to evaluate dependability of Internet-scale software by integrating all the aspects and analyzing system architecture from the most foundational elements. However, it is lack of such an evaluation model. An evaluation model of dependability for Internet-scale software on the basis of Bayesian Networks is proposed in this paper. The structure of Internet-scale software is analyzed. An evaluating system of dependability for Internet-scale software is established. It includes static metrics, dynamic metrics, prior metrics and correction metrics. A process of trust attenuation based on assessment is proposed to integrate subjective trust factors and objective dependability factors which impact on system quality. In this paper, a Bayesian Network is build according to the structure analysis. A bottom-up method that use Bayesian reasoning to analyses and calculate entity dependability and integration dependability layer by layer is described. A unified dependability of the whole system is worked out and is corrected by objective data. The analysis of experiment in a real system proves that the model in this paper is capable of evaluating the dependability of Internet-scale software clearly and objectively. Moreover, it offers effective help to the design, development, deployment and assessment of Internet-scale software.