@ProviderType
public interface ServiceUserMapped
The ServiceUserMapped is a marker service that can be used to
 ensure that there is an already registered mapping for a certain
 service/subService. A service reference targeting a
 ServiceUserMapped will be satisfied only if
 ServiceUserMapper.getServiceUserID will resolve the subService
 to an userID. For example setting the reference target to
 "(subServiceName=mySubService)" ensures that your component only starts when
 the subService is available. The subServiceName will not be set for mappings
 that do not have one, and those can be referenced with a negating target
 "(!(subServiceName=*))". Trying to reference a sub service from a bundle for
 which it was not registered for will not work.
 As the service user mapper implementation is using a fallback, it is usually
 best to use a reference target that includes both options, the sub service
 name and the fallback, therefore a target like
 "(|(subServiceName=mySubService)(!(subServiceName=*)))" should be used.