Research On The Transaction Of Composite Service

Web service is a new distributed computing model, which solves problems of inter-collaboration and inter-communication between heterogeneous systems from different enterprises or one enterprise. Transaction is an efficient mechanism to insure consistency and reliability of the application. Web service transaction is especially importance for the characteristic of relaxed coupling. Web service transaction, especially composite service transaction plays an important role in quality of service (QoS) and consistency and reliability for service computing.Composite service transaction is long transaction, so this paper presents a scope based embedded transaction model of composite service (SBET), which is extended from flat model of composite service transaction through further transaction partition. When transaction is cancelled, users can rollback to a certain consistent point selectively to insure semantic consistency. In order to guarantee QoS, a transaction recover algorithm supporting QoS restriction is presented, based on SBET of composite service. The algorithm can keep the area of compensation in a bottom scope, reduce the cost of compensation, insure QoS approaching to the best when transaction recovering, and can also insure semantic atomic of transaction. In order to enhance concurrency and insure correctness, a concurrency control algorithm of composite service transaction based on probability of conflict is presented. With fully considering of each concurrency control circumstance, the algorithm introduces the concept of semantic unit, lock on conflict class and critical section to guarantee semantic serializability of transaction scheduling, and avoids dead locking by priority rule of scheduling. At last, a prototype of composite service system supporting transaction named TCWS is designed, which solves the problem that mostly existing products or prototypes for composite service executing lack transaction supporting. The prototype is based on WS-Transaction specification. Besides coordinating transactional behavior of member services, it also provides functions of error recovery and concurrency control. Our research on transaction model of composite service, error recovery, concurrency control and composite service prototype system supporting transaction provides a new idea and a new approach for research on composite service transaction.