Working on the RESTifying Procurement show case I realized that it looks as if I had to revisit my approach towards service types. I have argued that a service type is constituted by the set of hypermedia semantics it makes use of. This seemed reasonable since a client developer needs to know at least a minimal set of the possible hypermedia semantics to expect from a service in order to write a client for a service of that kind.
Unfortunately this approach has some problems when services of different kinds use the same set of hypermedia semantics because the differentiating aspect is lost. I realized this because in the procurement example I am basically using a single media type but still have a range of services, for example supplier or carrier.
A possible solution to this issue is to have the all-encompassing media type define the service types. Such types are still necessary to enable lookup based on type, for example in order to find the carrier service of some external business partner. Looking for the procurement service doesn't make that much sense.