With the growing adoption of service-oriented computing, locating services becomes increasingly commonplace. Accordingly, a large number of systems for service discovery have been developed. Although all these systems perform the same function, they do it in lots of different ways. Finding commonalities of and differences between these systems can be hard due to the lack of criteria to compare and classify various discovery schemes. This paper identifies the processes of registration and look-up as a distinguishing feature of the various discovery systems. It describes the possible types of processes, shows how they are distributed across the lifecycles of the involved entities and classifies existing service discovery systems according to these criteria. Some hints are given on how the process-based view can help guide the selection of a particular discovery style for a problem at hand.