Availability and reliability analysis of computer software systems considering maintenance and security issues

AVAILABILITY AND RELIABILITY ANALYSIS OF COMPUTER SOFTWARE SYSTEMS CONSIDERING MAINTENANCE AND SECURITY ISSUES XIONG CHENG-JIE NATIONAL UNIVERSITY OF SINGAPORE 2011 AVAILABILITY AND RELIABILITY ANALYSIS OF COMPUTER SOFTWARE SYSTEMS CONSIDERING MAINTENANCE AND SECURITY ISSUES XIONG CHENG-JIE (B. Eng), WUHAN UNIVERSITY A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF INDUSTRIAL AND SYSTEMS ENGINEERING NATIIONAL UNIVERSITY OF SINGAPORE 2011 Acknowledgement First and foremost my greatest gratitude goes to my main supervisor, Prof. Xie Min, who supported me both in research and in practice all through my PhD candidature and whose wisdom is so charming that enlightened my research path. He is not only a well-respected advisor in research, but also more a spiritual tutor as well as a great friend. His knowledge and patience helped me transform from a beginner to a junior research without anxiety or frustration, which I am extremely grateful for. What is more, his noble personality and passion for research always spurs me to search more for research and life. I would have achieved much less if I had not been under his supervision. I am also heartily thankful to my co-supervisor, A/Prof. Ng Szu Hui, for her guidance and very detailed suggestions in my research, especially when I was undergoing the manuscript reviewing process. Her serious attitude towards research always reminds me to get rid of fickleness and utilitarianism, which was fatal in research. Her positive life style and friendliness also made me feel more inspired when I was her teaching assistant. I also gained lots of teaching experience from her. I am really grateful for her directions. Then I also want to express my gratefulness to the Department of Industrial and Systems Engineering and the National University of Singapore, for providing me scholarship and an excellent environment to study and research. I would have missed the most precious life experience if I had not won a chance to study in Singapore. I would like to thank A/Prof. Poh Kim Leng and Dr. NG Tsan Sheng, Adam, for serving as my oral qualification exam committee and provided me lots of deep insights for my further research. I also greatly thank Ms. Ow Lai Chun and Mr. Lau Pak Kai, for their excellent administrative and technical support to my PhD study. The warmest gratefulness also goes to A/Prof. Tang Loon Ching, who interviewed and encouraged me to join the Department of Industrial and System Engineering in Shanghai years ago. I would not be able to finish this thesis, or even to start writing this thesis, without their help. As a member of the Quality and Reliability Lab, I also benefited a lot from my lab mates. With all of them, I had a great post-graduate life for years. Special thanks goes to Li Yanfu and Shen Yan, who helped me a lot in life and at the same time in research, especially in research proposal and thesis writing. I would also like to thank Qian Yanjun, Yin Jun and Zhou Peng, for their help and advices that made my life and research easier. Finally, I would like to express my deepest thank to my parents, for their continuous encouragements and support for more than 20 years. Furthermore, to Mao Chengting, thank you for your understanding and encouragements. II Table of Contents Acknowledgement . I Summary . IV List of Tables . VII List of Figures VIII List of Notations and Acronyms . IX Chapter Introduction . 1.1 Focus of this thesis 1.2 Introduction to Quality Metrics of Computer Software Systems 1.2.1 Software Reliability . 1.2.2 Software Availability . 1.2.3 Software Service Reliability 1.3 External Factors Affecting Software Quality 1.3.1 Software Maintenance 1.3.2 Malicious Software 1.4 Research Motivation . 1.5 Thesis Organization Chapter Literature Review 10 2.1 Reviews on Software Reliability Modelling . 10 2.1.1 Basic Software Reliability Models . 10 2.1.2 Software Reliability Model Extensions . 22 2.2 Reviews on Software Availability Related Problems . 25 2.2.1 Software Maintenance and Software Availability . 26 2.2.2 Software Availability Assessment . 32 2.2.3 Malicious Software and Its Impact on Software Quality . 36 Chapter Software Availability Modelling and Application Extensions 40 3.1 Introduction . 40 I 3.2 Software Maintenance Activities and Software Availability 43 3.2.1 Decomposition of Software Maintenance Activities . 43 3.2.2 Software Maintenance Efforts and Software Maintenance Modeling . 46 3.2.3 Software Maintenance Modeling—A Numerical Example . 51 3.2.4 Validation of Software Maintenance Modelling 57 3.2.5 Software Availability Modeling Considering Software Maintenance . 58 3.3 Software Maintenance Policy Considering Software Availability Constraints 67 3.3.1 Re-investigation on Software Maintenance and Software Maintenance Policy 67 3.3.2 Software Maintenance Policy Modeling with Consideration of Software Availability and Cost Constraints 71 3.3.3 Validation of Policy Optimality—A Numerical Example . 75 3.4 Summary and Conclusion Remarks 80 Chapter Software Availability Assessment of N-version Programming Systems 82 4.1 Introduction . 82 4.2 Software Availability Modeling of N-version Programming Systems . 85 4.2.1 Structure Decomposition of N-version Programming Systems . 86 4.2.2 Proposed Model of Software Availability of N-version Programming Systems . 89 4.3 Impact of N-version Programming on Software Availability . 98 4.3.1 Failure and restoration rates for different versions of software . 98 4.3.2 Impact of N-version Programming on Software Availability: A Simulation Approach 101 4.3.3 Optimal Software Structure under Software Availability and Budget Constraints 112 Chapter Quality Degradation Analysis of Distributed Software Systems Considering Malware Attack . 119 5.1 Introduction . 120 5.2 Distributed Software Systems and Malware Epidemics: The Homogeneous Scenario 122 5.2.1 Modelling of Distributed System under Malware Attack: The Homogeneous Scenario . 123 5.2.2 Derivation of Software Service Reliability and Software Availability 129 5.2.3 Numerical Examples 131 5.3 Distributed Software Systems and Malware Epidemics – A Revisit 134 5.3.1 A Continuum State Reliability Model of Individual Nodes . 135 5.3.2 Virus Epidemic Model: The General Scenario 138 II 5.3.3 An Illustrative Example . 140 5.4 Service Reliability Modeling of Distributed System Considering Malware Epidemics . 145 5.4.1 Service Reliability Model without Communication Channel Failure 146 5.4.2 Service Reliability Model with Communication Channel Failure . 149 5.4.3 Computation of Service Reliability 151 5.4.4 A Numerical Example 153 Chapter Conclusions and Future Works . 160 6.1 Conclusions and Contributions . 160 6.2 Directions of Future Research . 162 Bibliography . 165 Appendix Service Reliability Calculation Algorithm 179 III Summary Reliability and availability have long been considered as critical metrics of high quality software systems. However, as plenty of research efforts have been devoted into the field of software reliability, only a little has been documented in the aspect of software availability. In the mean time, traditional ways of analyzing software quality often ignores the impact of environmental factors, such as software maintenance and software security issues. Realizing the importance of software availability to software quality study, this thesis first focuses on the modeling of software availability and some application extensions (Chapter 3). Then the model is further extended to analyze the availability issues of fault-tolerant software systems (Chapter 4), followed by a quality analysis of distributed software system considering malicious software attack (Chapter 5). The primal focus of this thesis is to develop a proper model to assess availability of software systems by analyzing feedback data (Chapter 3). To achieve this purpose, the origination of software availability problems is first analyzed. We assert that software maintenance is solely responsible for causing software availability problems and a rate-based model for describing software maintenance process is proposed. Based on the maintenance model, we incorporate the existing NHPP software failure models and propose a general approach for systematically calculating software availability. In order to check the effectiveness IV of our proposed models, we apply our model to a real-life industrial case to show its ability in helping seeking the optimal software maintenance policies. Besides the general modeling for calculating software availability, we also investigated the availability problems of fault-tolerant software systems (Chapter 4). The N-version programming technique is covered in this thesis and we proposed a Markov chain based software availability model to assess the availability of this special kind of software system. Interactions among different versions are explicitly considered and analyzed. Numerical analysis clearly reveals the positive impact of the N-version technique on enhancing software availability and we also propose a method for determining the optimal software structure from the availability costeffectiveness point of view. Moreover, as the threat of malicious software increases day by day with the quick popularization of internet, the analysis of the relationship between software quality degradation and malicious software attack forms another important part of this thesis. Hence, Chapter analyzed the problem of quality degradation of distributed software systems by considering malicious software attack. 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(2008).'Improving software reliability modeling using machine leaning techniques', International Journal of Software Engineering and Knowledge Engineering, 18(7), pp.102-117 178 Bibliography Appendix Service Reliability Calculation Algorithm Begin Rs (t )  P( E1 ) P(1  TE ) // initialize the system reliability, where P( E1 ) is the product of all links’ functioning probabilities in the 1st MTST: P( E )   pi1 , and P(1  TE ) can be obtained by directly i i using equation (5.29).   {} // initialize  which will be used to store the union of the events (E ) . For all  h*   s (1  h*  H )   [ E1      Eh*1 ] // let  store the union of the events (E ) that are the predecessors of the current event E h* . F  Reduction(, Eh* ) // F is the union of all preceding events (before E h* ) in which any link that is present in both E h* and any of its preceding events is deleted from those preceding events. S  Disjoint ( F ) // S is the sum of disjoint products representing F . This function is used to decomposes F into S to compute the probability of F . As F and E h* have no comment elements, the probability can be written as Bibliography P( E1      Eh*1  Eh* )  P( F  Eh* )  P( F ) P( Eh* ) Rs (t )  Rs (t )  P( Eh* ) P(S ) P(h*  TE ) End End Function Reduction(, Eh* ) // this function detects the links that appear in both  and E h* , and deletes those links from set  Begin for all li    (1  i  n ) // where n is the total number of links involved in the events union:  for all l hj*   h* (1  j  nh* ) // where nh* is the total number of links involved in the event: E h* if li  l hj* then ei  // to delete the links that appear in both  and E h* from set  , assign Boolean value of ‘1’ to those links end end F  // simplify the event union  with the Boolean values ‘1’ and assign it to F 180 Bibliography return F end function Function Disjoint ( F ) //this function decomposes the event F into a sum of disjoint products. It is noted that F has the following expression: F  E1( r )  E2( r )      Eh(*r)  ( E1( r )  E2( r )      Eh(*r) )   ( E1( r ) )   ( Eh(*r) ) where Ei(r ) is the reduced version of event E i (by applying the reduction function), and  is the exclusive operator. Begin S  ( E1( r ) ) // S is the set that stores the sum of disjoint products. This step initializes S . By the operation rule of exclusive operator, we have  ( E1( r ) )  e11  e11 e12  .  e11e12 .e1n1 e1n where n is the total number of links in the reduced event E1( r ) . for all  i  h * 1 // where (h * 1) is the total number of reduced events in the events union: F . // this step applies the operator  to decomposes Ei(r ) into S  S  ( Ei(r ) ) a sum of disjoint products. For instance,  ( Ei( r ) )  e1i  e1i e2i  .  e1i e2i .eni 1eni where n is the total number of links in the reduced event Ei(r ) . 181 Bibliography End Return S //expands S into the form of unions S  (e1 .en )  (e4 .em ) ) by the distributive low. End function 182 (e.g. [...]... quality of a software system Research in this area started from the technical point of view of software practitioners in software reliability (Jelinski and Moranda, 1972; Goel and Okumoto, 1979; Shanthikumar, 1981) and now has expanded to the consumers‘ point of view of software end users in software availability (Tokuno and Yamada, 2003) and software service reliability (Dai et al, 2003; Dai and Levitin,... most external factors, software maintenance and malicious software are of the most important factors that affect software quality 1.3.1 Software Maintenance Software maintenance is carried out during the operational phase and usually hampers normal software operation The software system usually cannot be online until software maintenance is done Two major characteristic of software maintenance is that... both software reliability and software service reliability What is more, for certain types of software such as open-source software, maintenance is so highly integrated with development that it is impossible to ignore the impact of software maintenance 1.3.2 Malicious Software The problem of software security has never been so severe, thanks to the prevailing Internet Malicious software, which is often... decade and are related to the foundations of this thesis Software reliability models and extensions serve as the basis of software quality research and this thesis is also motivated to extend the existing software quality research Thus, software reliability models will be reviewed first Then we focus on the problems of software availability The origination of software availability problem – software maintenance. .. namely correctness and timeliness This metric was proposed because together with software reliability and software availability, they represents three most basic requirements when people are using software systems – software needs to be correct (Reliability) ; software need to be accessible (Availability) and software needs to be stable (Service Reliability) 1.3 External Factors Affecting Software Quality... 2 Literature Review Software quality receives great attention of many software practitioners and various kinds of methods have been proposed to estimate software quality Other issues that directly affect software quality, such as software maintenance, software structure and software security issues have also been covered by many authors This chapter provides a detailed summary of the literature that... development of hardware technology and an increase population who are enjoying services provided by software, software availability related problems cannot be ignored (Tokuno and Yamada, 2003) 3 Chapter I Introduction When compared to software reliability, the literature in software availability is not vast and there is no standard definition of software availability Some authors regard software availability. .. Instant software availability at time t A i (t ) Average software availability over the period (0, t ] Di Initial hazard rate of sub version i Ei Initial failure restoration rate of sub version i Ctotal Total cost during the software operational cycle Co Cost of software operation Cm Cost of software maintenance Cr Risk cost if the software system is unavailable co Expected unit time cost of software. .. 1.2.1 Software Reliability There are many definitions of software reliability, but most authors consider that software reliability represents the probability of failure-free software operation for a specified period of time in a specified environment (Xie, 1991) Software reliability is widely regarded as the most important quality metrics and often used as an indicator for software release policy (Xie and. .. analysis of software systems cannot exclude external factors and many of the existing models do not provide satisfactory results in some occasions To overcome these drawbacks, it is necessary to take software maintenance, software structure and software security problems into the consideration of software quality metrics modeling As discussed above, many researchers have focused on three factors Software . II 3.2 Software Maintenance Activities and Software Availability 43 3.2.1 Decomposition of Software Maintenance Activities 43 3.2.2 Software Maintenance Efforts and Software Maintenance. traditional ways of analyzing software quality often ignores the impact of environmental factors, such as software maintenance and software security issues. Realizing the importance of software availability. 3.2.3 Software Maintenance Modeling—A Numerical Example 51 3.2.4 Validation of Software Maintenance Modelling 57 3.2.5 Software Availability Modeling Considering Software Maintenance 58 3.3 Software