Integrating Transactions into BPEL Service Compositions: An Aspect-Based Approach

The concept of software as a service has been increasingly adopted to develop distributed applications. Ensuring the reliability of loosely coupled compositions is a challenging task because of the open, dynamic, and independent nature of composable services; this is especially true when the execution of a service-based process relies on independent but correlated services. Transactions are the prototypical case of compositions spanning across multiple services and needing properties to be valid throughout the whole execution. Although transaction protocols and service composition languages have been proposed in the past decade, a true viable and effective solution is still missing. In this article, we propose a systematic aspect-based approach to integrating transactions into service compositions, taking into account the well-known protocols: Web Service Transaction and Business Process Execution Language (BPEL). In our approach, transaction policies are first defined as a set of aspects. They are then converted to standard BPEL elements. Finally, these transaction-related elements and the original BPEL process are weaved together, resulting in a transactional executable BPEL process. At runtime, transaction management is the responsibility of a middleware, which implements the coordination framework and transaction protocols followed by the transactional BPEL process and transaction-aware Web services. To automate the proposed approach, we developed a supporting platform called Salan to aid the tasks of defining, validating, and weaving aspect-based transaction policies, and of deploying the transactional BPEL processes. By means of a case study, we demonstrate the proposed approach and evaluate the performance of the supporting platform. Experimental results show that this approach is effective in producing reliable business processes while reducing the need for direct human involvement.