Research On Key Technologies For Trustworthy Service Composition

Software service and software service coordination represented by Web service have become a typical Internet application style. Service composition which integrates the functionalities of individual services to fulfill new and complex requirement has become an important manner for improving reusability of software and developing new Internet applications. However, the current service resources lack of the trustworthy and professional third party entities to authenticate guarantee for relevant properties. Moreover, service resources always belong to different autonomic domains, the execution process of services cannot be transparent to the customers and can be modified by service providers. Therefore, service resources have the nature of nondeterminacy and uncontrollability, the quality of service is unknown at moments. It is very obvious that the trustworthiness problem of whole application, namely, the problem of trustworthy service composition, has become a challenging and critical problem of service composition.On the basis of analyzing the challenges of service composition at the aspect of trustworthiness, the dissertation have mainly studied on several key problems including service selection strategy, composition plan selection, reducing fault-tolerant cost, mechanism of evolution and service access control. We present trust concept framework of service composition which includes identity trustworthiness, capability trustworthiness and behavior trustworthiness, and then start from the point view of reusability, shareability, reliability, availability and collaboration, we present several relational mechanisms to increase service composition entire trustworthiness. Our contributions have become systematical trustworhty service composition supporting framework which is helpful for providing effective trust-guarantee mechanisms for network application based on software service coordination. The contributions of the dissertation are listed as follows:(1) On trustworthy services selection: Trustworthiness is user's subjective feeling, and for this reason, it not only needs to meet the objective accuracy of QoS, but also needs to consider the users'individualized requirements, but existing service selection strategy lacks of preference support. Aiming at the problem, by borrowing some ideas of Internet recommendation system, we propose preference recommendation based trustworthy service selection algorithm. First, we find a group of recommenders which have similar rating levels according to the historical evaluating information; then, compute the trustworthiness of service by adding recommenders'evaluation of estimate weighting to provide grounds for choosing service. Our experimental results show that our method can find out proper services to meet user's preference requirements effectively, and solve the weakness of recommender systems, such as cold start, inaccurate recommendations and dishonest evaluation. Compared with the similar works, our method focuses on the similarity of users'personal experience, and considers the recommending level and relative domain degrees as well. Therefore, it is more suitable for meeting the users'individual requirements, thus greatly increasing users'faith on service.(2) On composition plan selection: It is the main reason for increasing fault-tolerant cost that without theory guiding the choice while select an optimal one among large number of composition plans. So, to some extent, it restricts the effect of fault tolerance and makes fault tolerance unworthy. To this problem, we present nine pieces of functional split principles based on the analysis of high-cost bring from service redundancy and replanning, in order to reduce the cost of fault tolerance. Following these principles is helpful for the designer to select the proper service granularity and reduce the coupling degree of services, moreover, it will be beneficial to coordinate services as well as reduce the cost of fault tolerance. Compared with the similar works, our work emphasizes on the support to fault-tolerant mechanism in design time which is the most important but always ignored part by most researches.(3) On reducing failure cost: The failure of composite service is inevitable, which would bring high quota compensation cost, and result in increase of expenses and reduction of users'reputation. For that, based on analyzing and defining the cost of compensating transactions, we present a sub-transactions committing delay algorithm in the backgroup of service composition with transactional characteristic. Sub-transactions can determine the time of committing according to both the cost of compensation and the state of execution dynamically which can turn potential compensation into rollback. The correctness of proposed algorithm is proved, and simulations show that the algorithm can confine the compensation sphere and reduce the cost of compensation when the transaction fails. Compared with the similar works, our work not only classifies compensating operation accurately, but also defines the cost of compensation exactly, while current work largely considers the compensation as two-value which makes against the description the difference of compensation and reduces the effect of optimization on scheduling algorithm based on the cost of compensation.(4) On evolution of service composition: It is impossible to find out the method to get availability and reliability done once and for ever in design time, so a feasible technical way is monitor and evolution. To meet the requirement, we present QoS-driven service composition evolution. Based on the evolutionary model of service compositon, we analyze and summarize the specific challenges of service composition evolutionary mechanisms which include general capability of monitor implantation, multidimensional decision making model, increasing stability during the evolution and preventing from shaking of system. After that, we present several solutions based on monitoring software production line, multidimensional service's QoS decision model, principle of design based on coupled model and discrete trigger mechanism of evolution effectively. We attempt to build the evolution model of service composition both in microscopic view and macroscopic view, and then provide necessary services flexibly according to the character of application. Simulation experiments and system indicate the validity of evolutionary mechanisms, moreover, by adjusting parameters appropriately, we can enhance stability and reduce shaking of the system during the process of evolution.(5) On servcie access control: From the trust point of view, people first consider the trustworthiness of service provider. However, under some circumstances, service providers may not trust that users can use their services correctly, whether this misuse happens through malice, stupidity, or oversight is unimportant. It may affect the state of the services which result in reducing the shareability and disturb proper operation even more. To solve this problem, we introduce the term SDOS (Semantic Denial of Service) combine with classical case to describe such problems and then we present a user trustworthiness based lightweight access control which recessively defines users'activities by adjusting two parameters: resources hold duration and compensation intensity. Through the experiments, we find that our proposed mechanism can restrain the SDoS attack effectively.