Abstract--The paper proposes a model which allows integration of services published by independent providers into scientific or business workflows. Optimization algorithms are proposed for both distribution of input data for parallel processing and service selection within the workflow. Furthermore, the author has implemented a workflow editor and execution engine on a platform called BeesyCluster which allows easy and fast publishing and integration of scientific and business services. Several tests have been implemented and run in BeesyCluster using services for a practical digital photography workflow with and without budget constraints. Two alternative goals are considered: minimization of the execution time with a budget constraint or a linear combination of cost and time.