We present an optimization approach for service compositions in large-scale service-oriented systems that are subject to Quality of Service (QoS) constraints. In particular, we leverage a composition model that allows a flexible specification of QoS constraints by using constraint hierarchies. We propose an extensible metaheuristic framework for optimizing such compositions. It provides coherent implementation of common metaheuristic functionalities, such as the objective function, improved

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... tion or neighbor generation. We implement three metaheuristic algorithms that leverage these improved operations. The experiments show the efficiency of these implementations and the improved convergence behavior compared to purely randomized metaheuristic operators.