Service outsourcing is a business paradigm in which an organization has a part of its business process performed by a service provider. Process views are pivotal to support this way of working. A process view shields secret or irrelevant details from a private business process, thus allowing an organization to reveal only public, relevant parts of its private business process to partner organizations. This paper introduces a specification framework to support service outsourcing using process views. To enable the construction of process views at various levels of detail, the framework defines several projection relations between process views and the underlying internal processes. To allow consumers and providers of process views to establish an outsourcing relation, the framework defines several matching relations between the respective views that are comprehensive and flexible for service outsourcing. A proof-of-concept prototype tool implements the framework, which is applied in a case study.