1. A system for selecting services that are used for a composite service, the system comprising: an accessing unit configured to access: tasks of the composite service, transactional requirements of the tasks, services that are configured to fulfill the tasks, and transactional properties of the services; and a processing unit configured to: compute conditions for services that are configured to fulfill a task and select a service configured to fulfill the task and having transactional properties that fulfill the conditions, wherein the conditions are computed using data comprising the transactional requirements of the tasks.