In Service-oriented Architectures, business processes are realized by composing loosely coupled services. With the ongoing success of Web services technologies, the invocation of Web services goes beyond enterprises' borders. So, besides implementing required services within one enterprise, services can be purchased from external service providers. With a growing number and variety of services, enterprises can choose between functionally equivalent services at different cost and quality levels. The paper at hand addresses this service selection problem considering complex workflow patterns. Aggregation functions for different quality of service parameters are proposed and a linear optimization problem is formulated, which can be solved using integer linear programming techniques or by applying heuristic solutions.
