A service , the fundamental unit of a federation, is an entity that sits on the network ready to perform some kind of useful function. Once a service becomes part of a federation, it then can be used by client programs, other services, or users. In this example, the client program builds a federation consisting of itself, the image storage service, the persistent storage service, and the color printing service. Jini technology consists of a programming model and a runtime infrastructure. The runtime infrastructure resides on the network and provides mechanisms for adding, subtracting, locating, and accessing services as the system is used.
Services use the runtime infrastructure to make themselves available when they join the network.
A client uses the runtime infrastructure to locate and contact desired services. Once the services have been contacted, the client can use the programming model to enlist the help of the services in achieving the client's goals. Lookup services are the central organizing mechanism for Jini technology-based systems. When devices are plugged into the network, they register themselves with a lookup service and become part of a federation. When clients wish to locate a service to assist with some task, they consult a lookup service.