Research On Reliability Evaluation For Component-based Software System

The reliability evaluation for component-based software systems is an important method to guide software design and development. The evaluation result is to measure whether the software can be released. Software reliability problems had led to many serious accidents. Component-based system reliability evaluation has a very important role in software engineering. Evaluation techniques are receiving more and more attention. It refers to the component reliability evaluation in a system, sensitivity analysis of the component reliability on the system reliability, constructing system reliability model, and the reliability evaluation of the system. In which, the component reliability evaluation in a system, and constructing system reliability model are the difficult problems. The information, which developer can obtain during system development, is different. Therefore, in order to get a more accurate assessment results, it is necessary for developers to combine the information obtained and use appropriate methods when they build a reliability evaluation model. This paper discusses the system reliability evaluation making use of probability theory and mathematical statistics, stochastic process theory. The discussion includes the selection of component reliability model, the effective behavior reliability of the components in the system, the reliability related to the component location in the system path and the reliability evaluation of component assembly code.First, as the specialties and resources of the components may be different, not all components using a fixed reliability model can get accurate results in system reliability assessment. In order to get a more accurate assessment, combining the single component reliability model with the component-based reliability model, this paper proposes an optimal selection evaluation method. First, according to the historical data of each component, using the maximum likelihood estimation selects the most suitable model for each component, so that the reliability assessment deviation of each component is the minimum; then according to the relationships between the components and the component usage in the system, the system reliability is evaluated. This method considers the historical data and usage of the components and selects appropriate assessment model for each component, and thus it can get a more accurate assessment than using a single model.Second, aiming at the inaccurate results of the reliability assessment methods caused by without taking full account of the effective behavior of the components, the paper studies the acquisition of component effective behaviors, the evaluation of component effective reliability and the system reliability evaluation method. A method with consider effective component reliability is proposed. First, the effective component behaviors described in the scenario protocol are extracted by analyzing the design models of the system. Then the evaluation methods for the reliability of component external behavior are found. They include the metadata method, the approximate estimation method and simulation method. Based the methods above, three evaluation methods for effective component reliability are discussed. They include simulation method, direct calculation method and dynamic access method; finally, the system reliability model is constructed using Markov theory, and then the system reliability is obtained. The proposed methods are illustrated by a case. The results showed that after considering the effective behavior of the component, the component-based system reliability assessment is more reasonable.Third, the reliability evaluation methods for component-based system assume that the component reliability is a known fixed value, and do not consider the difference between different locations of the same component in the execution path, and the change of the component reliability increasing with time, and thus the results of the assessment has a greater deviation to the actual value. Aiming at the problem, the dissertation discusses a system reliability model based on the component location on its execution paths. First, the calculation method for the probability of the component execution path is discussed; then how to calculate the actual execution time of the component in a system, according to the running time of the system and the location of the component, is presented. How to calculate actual component reliability on different paths using its actual running time is also discussed. The calculation methods for the reliability of the execution path and system are described. The reliability sensitivity analysis are introduced. The experiment results show that the method can be more reasonable to predict the reliability of the system at any time point, and it is different which the changes of component reliability at different time influence the reliability of the system.Finally, in order to solve the problem of which the reliability models for component-based system do not consider the reliability of the assembly code, the reliability evaluation method with considering the reliability of assembly code is proposed. First, the component assembly structures are analyzed; then the existence form of the assembly code for the object-connected structures, the interface-connected structures and plug-socket structures are discussed; the reliability evaluation for the assembly codes and system are presented. Based on the research above the reliability assessment methods for mixed structural system are introduced. Finally, the effectiveness of the proposed method are verified by the examples. The reliability evaluation methods with considering the reliability of the assembly code are consistent with the practice, and therefore more practical.In summary, the dissertation researches on system reliability evaluation based on the characteristics of component-based system. The dissertation discusses how to avoid the errors caused by the component reliability models, discusses the method of using component effective reliability to improve the accuracy of reliability evaluation, and discusses how to improve the accuracy of the system reliability evaluation by obtaining the accurate run time of the component. Finally, the dissertation discusses the evaluation method with considering the assembly code to improve the accuracy of the system reliability evaluation.