Research Of Composition And Concurrent Control For Transactional Web Services

In recent years, with development and advancement on the new generation of large-scale Internet applications, such as grid computing and cloud computing, especially where three service computing patterns including Infrastructure as a Service (IaaS), Platform as a service (PaaS), Software as a service (SaaS) have been applied successfully, demonstrates that the technology of web service has become one of the most important technologies in current main distributed applications. Especially, with growing demand for network users, how to quickly composite these existing single web services in Internet into one more complex add-value web service, becomes an important pursuing goal by both industry and academia.However, due to instability and complexity in Internet environment, how to guarantee the correctness and consistency for a transactional composite web service, has become one of key challenging problems in web service composition arean. For the reason that a transactional web service has several inherent characteristics, including autonomy, distribution, heterogeneity, long running and so on, it's very difficult to migrate existing traditional methods on transaction process into web service environment. Although, there are several study work on transactional web service composition (TWSC) and concurrent control over TWSC, many challenges have to be addressed. In this paper, we focus on corresponding research work on TWSC, coordination and concurrent control for TWSC. The major contributions and innovations are summarized as follows.(1) Studying related work involving aspects of traditional transaction model and transactional web service coordination specifications:First of all, we introduce advantages and disadvantages of these traditional transaction models. Then, we show that it's very difficult for these traditional transaction models to adapt into web service environment. Further, we give existing transactional coordination specifications of web services, on which corresponding unresolved problems have been also presented.(2) Studying and presenting the approach of optimal web service composition under satisfying both constraint of relaxing atomicity and end-to-end QoS constraint. In the area of current research on QoS-aware web service composition, few of work study the problem of web service composition, considering both the two aspects including transaction constraints and QoS end to end constraints. To ensure relaxing atomic for any composite web service, we propose a group of building rules and reduction rules, which are used to build the service candidate graph (SCG) model for any abstract composite web service. Additionally, the correctness including both reliability and completeness for the model has also been proved. Thus, TWSC problem is transferred into one variant issue of solving the single source shortest path problem. Then we present one kind of near-optimal QoS-aware TWSC approach based on proposed SCG model. Finally, comprehensive experiments are conducted based on a real-world web service QoS dataset. The experimental results show that our approach has better performance over other competing selection approaches on success ratio and efficiency.(3) Studying and presenting a method of QoS optimal web service composition on the basis of predetermining transaction properties of each constituted web service:In real application fields, it exists the situation that transaction semantics of an abstract composite web service, which cause to their constituted web services with invariant transactional properties. With analysing historical logs of execution for any abstract composite web service, we present an extended petri-net formalizing model to enable the proposed recovery algorithm. Meanwhile, our formalizing model can be support of any abstract composite web service with any level nested subtransactions. Afterwards, we give an application case of ensemble prediction to show the formailzing model. With the application case, we propose a method to evaluate relative importance for each constituted web service in an abstract composite web service. After that, we propose a linear planning method to determine local constraints for each constituted web service, which will enable the near optimal QoS web service composition. For the reason that we can decrease the scale of existing candidate paths by local constraints, our approach can obtain a better performance comparing to other methods. Finally, the experiments has been conducted to prove the outstanding performance for our approach.(4) Under relaxed transaction atomicity, studying and presenting a new method of QoS service composition based on the trad-off between expected risk and global QoS utility:Due to the nature of long running web service, it will lead to large losses to guarantee global consistency of transactional composite web service, once a failure in the composite web service encountered. In order to address this problem, based the proposed SCG model built in section 3, we propose a backward searching-based near optimal web service composition approach, which regards two objectives including global QoS utility and expected risk value. The experiments show that, our approach can reduce average losses caused by failures for any abstract TCWS. Aditionally, the approach can own better performances on the global QoS utility and the running time.(5) Studying concurrent coordination mechanism for TWCS with open multi-level nested transaction model:Due to existing coordination specifications of transactional web services are just only adapt to the web service with transactional property of compensatable, and they don't give details on how to control concurrent execution among transactional web services, we firtly extend to current web service specifications presented by international organizations such as OASIS etc., then present one new coordination framework for transactional web services. Furthermore, we present a corresponding web service coordination protocol. Based on the proposed framework, two security execution rules, such as the security rule for web service execution and the security for web service coordination to execute the operation of close, have been presented. Meanwhile, we give formal definition for our considering problem. Afterwards, we propose several distributed algorithms for our proposed concurrent control mechanism:1. We propose a web service schedule algorithm considering the risk of submitting single web service in each local provider of resource; 2. We present a risk evaluating algorithm in distributed environment; 3. Based on two objective involving both global throughout and failure risk, we propose a Distributed control strategy for each web service of executing completion operation. Comparing to other related concurrent control mechanism, our mechanism has several merits:Firstly, it can enable coordination for multi-level nested TCWS and support heterogeneous nature of web service. Secondly, it could decrease failure risk caused by cascading abort in concurrent execution among multi-TCWS.