With the advent of Service Oriented Architecture organizations have experienced services as a platform-independent technology to develop and use simple internal applications or outsource activities by searching for external services, thus enabling inter-organizational interactions. In this scenario, services are units of work provided by service providers and offered to the other organizations involved in a collaborative business process. Collaboration should be facilitated by guaranteeing a homogeneous description of services at the right level of granularity. We propose a methodology to support the designer of a business process in the identification of services that compose the process itself. The methodology should allow collaborative partners to standardize process modelling through component services, enabling effective interorganizational service discovery. The methodology is presented by means of a running example in a real case scenario.