The coordinator cannot know the details of how every transactional service is implemented. In fact this knowledge is not even necessary for it to negotiate a transactional outcome. It treats each service taking part in a transaction as a participant and communicates with it according to some predefined participant coordination models appropriate to the type of transaction. When a web service receives its first service request in some given transaction, it enrolls with the coordinator as a participant, specifying the participant model it wishes to follow. The context contains a URL for the endpoint of the coordination service which handles enrollment requests. So, the term participant merely refers a transactional service enrolled in a specific transaction using a specific participant model.