Subdivisions of the theory of service. Theory is created by doing research, but the difficulty is that in order to be effective, research projects can only study a few limited questions at a time. The number of important questions that any field of service has to deal with, is many times larger than an empirical research project could handle. If somebody thus wants to make a larger compilation - such as a "Handbook of the xx-service" - this has to be made not from empiria, but instead by studying numerous earlier published research reports. Indeed, such service-specific compilations of theory have been made for many important branches of service. They will not be enumerated here, the main reason for it being that they are too numerous and besides they often soon lose their actuality because of the swift development of the technologies of service.