Middleware
In an n-tier system, special software called middleware enables the tiers to communicate
and pass data back and forth. Some IT professionals refer to middleware as the glue that
holds clients and servers together. The broader definition shown in Figure 10-18 on the
next page states that middleware is software that mediates between an application
program and a network.
Middleware provides a transparent interface that enables system designers to
integrate dissimilar software and hardware. For example, middleware can link a
departmental database to a Web server, which can be accessed by client computers via
the Internet or a company intranet. Middleware also can integrate legacy systems and
Web-based applications. For example, when a user enters a customer number on a
Web-based inquiry form, middleware accesses a legacy accounting system and returns
the results