Per-flow Optimal Service Selection for Web Services Based Processes

With the development of the Service-Oriented Computing (SOC) paradigm, flexible business processes can be defined from independently developed services. Multiple services corresponding to the same functionality but characterized by different Quality of Service (QoS) attributes can be offered by different service providers and the best set of Web services can be selected at run-time in order to maximize the QoS for end users. In the literature many approaches have been proposed for the optimal service selection which is usually performed on a per-request basis, i.e., considering a single process invocation. In this paper we propose a broker-based framework which solves the optimal service selection on a per-flow basis. Multiple applications, defined as different BPEL processes are considered at the same time and multiple requests to the same process are optimized concurrently. Service selection is formulated as a constrained non-linear multi-criteria optimization problem and an heuristic algorithm is proposed to determine a scalable and efficient solution. A comparison with top performing state-of-the-art approaches for a number of different scenarios of interest is also provided. Results show that the overall optimization time reduction which can be achieved by our solution is proportional to the system incoming workload. Order of magnitudes optimization time improvements can be obtained if compared to alternative methods. Moreover, our solution is robust to workload prediction uncertainty.