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build autonomous control modules, which are the building blocks of a
distributed system.
Flexibility : control modules execute multiple concurrent tasks and offer
services to other control modules. They interact with each other accord-
ing to a variety of synchronization modes and communication protocols.
Maintainability : the framework allows the incremental development of
control modules, whose capabilities can be extended by adding new types
of task and communication protocols.
We need to develop a test application using the library components of the
MMI framework. For the sake of simplicity, the test application is a small
server system that demonstrates the correct behaviour of the frame-
work components with regard to the main features described above.
The client is a graphical user interface that displays a jogging track. The
track is made up of a graph of lay-bys where the runner can rest. The user
can select the path that the runner will follow repeatedly and the runner's
speed. A path is a sequence of adjacent lay-bys.
The server is the manager of the jogging track. Since many runners can be
on the track simultaneously, it guarantees that every lay-by is occupied
by only one runner at a time. When a runner is going to move towards a
lay-by that is currently occupied, the server stops the runner until the
lay-by is free.
The client can be a standard application or an applet, or even an HTML
page that offers a textual representation of the jogging track and of the
position of each runner.
Architecture and planning
The system architecture is made up of three main subsystems as described
in Figure 19.1. Control module is the basic component of the MMI frame-
work that is specialized for each distributed system in a collection of server
components and a collection of client components. Clients and servers
inherit all the mechanisms and features to handle multiple tasks concur-
rently, to synchronize their activities and to communicate through the
The development process of the MMI framework is organized into three
phases that produce three prototypes.
Prototype 1: Synchronous communication . The components library
enables the development of multi-task control modules and allows them to
interoperate using Java RMI. The test application exemplifies synchronous
and deferred-synchronous communication between client and server.
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