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In a Service Oriented Architecture (SOA) business processes are commonly implemented as orchestrations of web services, using the Web Services Business Process Execution Language (WS-BPEL). Business processes not only have to provide the required functionality, they also need to comply with certain Quality-of-Service (QoS) constraints which are part of a service-level agreement between the service provider and the client. Different service providers may offer services with the same functionality but different QoS properties, and clients can select from a large number of service offerings. However, choosing an optimal collection of services for the composition is known to be an NP-hard problem.We present two different approaches for the selection of services within orchestrations required to satisfy certain QoS requirements. We developed two algorithms, OPTIM_HWeight and OPTIM_PRO, which perform a heuristic search on the candidate services. The OPTIM_HWeight algorithm is based on weight factors and the OPTIM_PRO algorithm is based on priority factors. We evaluate and compare the two algorithms with each other and also with a genetic algorithm.

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