AR.1. Introduction

This document describes the high-level architecture of system of Jini technology-enabled services and/or devices (Jini system), defines the different components that make up the system, characterizes the use of those components, discusses some of the component interactions, and gives an example. This document identifies those parts of the system that are necessary infrastructure, those that are part of the programming model, and those that are optional services that can live within the system.

AR.1.1. Goals of the System

A Jini system is a distributed system based on the idea of federating groups of users and the resources required by those users. The overall goal is to turn the network into a flexible, easily administered tool with which resources can be found by human and computational clients. Resources can be implemented as either hardware devices, software programs, or a combination of the two. The focus of the system is to make the network a more dynamic entity that better reflects the dynamic nature of the workgroup by enabling the ability to add and delete services flexibly.

A Jini system consists of the following parts:

• A set of components that provides an infrastructure for federating services in a distributed system

• A programming model that supports and encourages the production of reliable distributed services

• Services that can be made part of a federated Jini system and that offer functionality to any other member of the federation

Although these pieces are separable and distinct, they are interrelated, which can blur the distinction in practice. The components that make up the Jini technology infrastructure make use of the Jini technology programming model; services that reside within the infrastructure also use that model; and the programming model is well supported by components in the infrastructure.

The end goals of the system span a number of different audiences; these goals include the following:

• Enabling users to share services and resources over a network

• Providing users easy access to resources anywhere on the network while allowing the network location of the user to change

• Simplifying the task of building, maintaining, and altering a network of devices, software, and users

The Jini system extends the Java application environment from a single virtual machine to a network of machines. The Java application environment provides a good computing platform for distributed computing because both code and data can move from machine to machine. The environment has built-in security that allows the confidence to run code downloaded from another machine. Strong typing in the Java application environment enables identifying the class of an object to be run on a virtual machine even when the object did not originate on that machine. The result is a system in which the network supports a fluid configuration of objects that can move from place to place as needed and can call any part of the network to perform operations.

The Jini architecture exploits these characteristics of the Java application environment to simplify the construction of a distributed system. The Jini architecture adds mechanisms that allow fluidity of all components in a distributed system, extending the easy movement of objects to the entire networked system.

The Jini technology infrastructure provides mechanisms for devices, services, and users to join and detach from a network. Joining and leaving a Jini system are easy and natural, often automatic, occurrences. Jini systems are far more dynamic than is currently possible in networked groups where configuring a network is a centralized function done by hand.

AR.1.2. Environmental Assumptions

The Jini system federates computers and computing devices into what appears to the user as a single system. It relies on the existence of a network of reasonable speed connecting those computers and devices. Some devices require much higher bandwidth and others can do with much less—displays and printers are examples of extreme points. We assume that the latency of the network is reasonable.

We assume that each Jini technology-enabled device has some memory and processing power. Devices without processing power or memory may be connected to a Jini system, but those devices are controlled by another piece of hardware and/or software that presents the device to the Jini system and itself contains both processing power and memory. Architectures for devices not equipped with a Java virtual machine ^[1] (JVM) are explored more fully in the Jini Device Architecture Specification.

^[1] *As used in this document, the terms “Java virtual machine” or “JVM” mean a virtual machine for the Java platform.

The Jini technology infrastructure is Java technology centered. The Jini architecture gains much of its simplicity from assuming that the Java programming language is the implementation language for components. The ability to dynamically download and run code is central to a number of the features of the Jini architecture. However, the Java technology-centered nature of the Jini architecture depends on the Java application environment rather than on the Java programming language. Any programming language can be supported by a Jini system if it has a compiler that produces compliant bytecodes for the Java programming language.