It exemplifies the separation of concerns between user interface, communi-
cation and back-end computation. The information system is structured
according to the three-tier architecture. The user interface at the super-
market counter consists of a touch screen and a bar code reader; information
on the products' prices and stock levels are kept in a separate server
machine. The server machine centralizes most of the computing activities
and allows monitoring of the ongoing activities by the sales manager.
Chapter 15 (Geographic information system) presents the development
of a simple geographic information system (GIS). The goal is to exemplify
the process of integrating disparate technologies and, in particular, data
storage in a database, data transmission using sockets and data visualization
through Java Applets.
Chapter 16 (Ubiquitous email) addresses the problem of developing an
email server which provides nomadic access to the email of its users by sup-
porting several communication channels and communication media, such
as wired and wireless internet. The ubiquitous email server can therefore
be considered a sort of mediator broker, which offers mediation support
between a standard mail server and its users by enhanced mail access with
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