A memetic algorithm-based indirect approach to web service composition

Web service composition is a popular area of investigation, since it encourages code reuse as opposed to re-implementing already existing functionality modules. Performing such compositions manually can be quite time-consuming, since the functionality of each service included in a solution must be fulfilled, while at the same time selecting candidates with the best possible quality of service attributes. This work proposes a memetic algorithm that can perform Web service composition in a fully automated manner, optimising a sequence of services that is then decoded into the final solution. The key advantage of this representation is that it separates the quality optimisation technique from the enforcement of correctness constraints, thus simplifying the overall composition process and preventing solutions from being overly constrained. While this indirect composition approach has been investigated earlier, the previous representation relied on weights for establishing a service sequence and used PSO as the optimisation technique. In this work, on the other hand, sequences are directly represented using a vector of services, which reduces the overall search space. Additionally, the memetic algorithm employed in this work is better at exploring solutions within promising areas of the search space. Experiments were conducted comparing the memetic approach with the previously proposed PSO, with two key findings. Firstly, the new representation reduces the overall execution time while maintaining the original solution quality. Secondly, the use of the memetic local search improves the overall quality of solutions, though it may incur longer execution times.