Research On The Development Method Of Target-based High-confidence Adaptive Fault-tolerant Software

As Internet software centralized information systems have deeply impacted most aspects of our social and economical life, the Internet based distributed computer systems and open network environments also have increased complexity, error-proneness, and instability of systems, which makes them huge and hard to manage. As defects and safety hazards seem hard to avoid, systems are becoming more vulnerable, and sometimes even not work as expected. All of these factors have brought new problems and challenges to the dependability of software systems.Software fault-tolerance technology is an important method to guarantee the dependability of the systems. But, the traditional software fault-tolerance methods have several disadvantages:costs are too high that multiple redundant implementation versions are needed; low modularization makes modeling and predictive analysis hard; unable to adapt various and complex run-time ineffectiveness. In recent years, people in the field of dependable software research are tended to associate their research with self-adaptive software systems. Comparing to traditional redundancy and diversity based fault-tolerance methods, self-adaptive systems can dynamically adjust their behaviors and structures, thus improve reliability at run time. This leads to a more flexible and effective way towards software dependability.Based on comprehensive study of this area, this dissertation presents theories and technologies that cover the whole life cycle of development of dependable software systems, and provide practical guides. This dissertation propose a more systematic, effective, and practical self-adaptive fault-tolerance solution, to combine theories and technologies scattered among reliable software system research:from modeling of reliable requirement, to design of self adaptive fault-tolerance software architecture, as well as system implementation and run-time monitoring and diagnosis, we tight designs of products of the software system development stages, and form a integral theoretical system.To fix the disadvantages of current goal-oriented requirement modeling methods in self-adaptive software system, and to support requirements of runtime monitoring, diagnostics and fault tolerance in software systems, this dissertation at first extends the description framework, goal types and goal relations of KAOS requirement modeling methodology. And based on this, this dissertation proposes a systematical and reliable requirement modeling method for the goal oriented self-adaptive software systems. Comparing to the current similar works, our method refines many aspects in requirement modeling process, and adds the support for modeling self-adaptive infrastructure and self-adaptive scenario.Due to the concept differences between requirement models and software architecture models and the relatively independent evolutions, translating requirement models to software architecture model is very difficult. Aiming to solve this problem, based on the reliable goal models, this thesis proposes a systematic derivation method for self-adaptive software architecture model. From two architectural design views, we respectively discuss the ways to derive software architecture model from goal model according to different kinds of goal refinement patterns. Then we propose a tracking meta-model from goal model to software architecture model that guarantees the track-ability and consistency in the whole derivation process.Based on the current implementation of self-adaptive fault tolerance techniques, this thesis raises a boarder fault-tolerance concept:1) For fault-tolerance objects, besides defects in design and implementation of software itself, we also take changes and invalidation of runtime environment, and non-functional conflicts in system into consideration 2) For fault tolerance targets, we don't emphasize absolute reliability but sustainability to guarantee the key services, as our mail goal. Based on this we use kinds of fault tolerance methods to optimize the execution of whole system. This dissertation mainly discusses how to carry out runtime self-adaptive activities like monitoring, analysing, planning and execution, which focus on the software architecture.To relieve the difficulty in runtime monitoring of the self-adaptive systems, based on the goal model, this thesis proposes a runtime monitoring and diagnosing approach. By integrating requirement reasoning, runtime monitoring and self-reconfiguring, it can perform fault tolerance behavior based on the detection of system errors and diagnostic results. From the definition of monitoring events, to generating and weaving the monitoring code, and then diagnosing and responding to the monitoring results, this thesis provides a complete solution for runtime monitoring of the reliable requirements.Finally, we also design the corresponding support platform and implement a prototype system.