Linux Network Programming, Part 3

This month we are presented with an introduction to the networking of distributed objects and the use of CORBA.
Multi-tier Network Computing

CORBA is an example of what is termed “middleware”--a technology that enables the separation of applications into three distinct sections (see Figure 5):

  1. The presentation, or user interface, tier

  2. The business logic, or control, tier

  3. The data storage tier

Figure 5. Three-Tier Network Computing

The presentation layer could be an HTML form or a Java applet (as in Figure 5). Extracting the control logic from the presentation allows you to network-enable the presentation of your application.

It also allows the end user to use less expensive hardware to interact with the application, since their equipment is now responsible only for rendering the information supplied to it by the control logic. In addition, the presentation system does not need to have any knowledge of where the data originally came from or in what format it is stored in the database—all it needs is the interface to the middle layer.

The control logic can perform access management, alter the view of the information as required to enable different users to view different subsets of the same data—perhaps for security reasons. For example, a doctor in a hospital may want to see the patient's medical history, whereas someone from the finance department should only be able to see billing information. In Figure 5, either Java or CORBA performs the role of the business logic.

By separating the control logic from the data store, you gain the benefits of distributed computing. Your logic can encapsulate database access, providing you with scalability and fault-tolerance for mission-critical data. All sources of corporate information can be integrated via the control logic to achieve what is termed a “data warehouse”--allowing all the information to be accessed via a single interface (depending, of course, on security clearance).

Legacy systems can be encapsulated, thereby protecting your existing investments. By standardizing the interface between the business logic and the data, you can more easily replace or upgrade database systems. The desktop machines (responsible for presentation) do not need to be modified. The task of replacing a database becomes solely concerned with that action—moving data from one database to another, without affecting the other components of the system.

The control logic can also augment the capabilities of the data storage system, performing additional features, such as searching the information for non-obvious trends (a process called “data-mining”).

The separation of application systems into a number of distinct tiers, and standardizing the interfaces between these tiers, ensures that when you make a modification to one layer, the effect of this change on your entire architecture is localized.


In this article, we introduced the Common Object Request Broker Architecture, a developer's tool in implementing applications based on distributed object technology. We also discussed the benefits of an object-oriented approach to network programming over traditional functional approaches, such as the use of RPCs. Finally, we introduced one of the main interests in CORBA technology—enabling the deployment of business applications on a network using a multi-tiered approach.

The next article will discuss the various ORBs available for Linux and how to begin programming with CORBA.


Acronymns and Abbreviations

Ivan Griffin is a postgraduate student in the ECE department at the University of Limerick, Ireland. His interests include operating systems, broadband networks and multimedia. He maintains a page of Linux WWW resources at, and his e-mail address is

Mark Donnelly is also a postgraduate student in the ECE department at the University of Limerick, Ireland. Mark is interested in Aikido, Linux, CORBA, Distributed Agents and Alpha World. His e-mail address is

Dr. John Nelson is a senior lecturer in Computer Engineering at the University of Limerick, Ireland. His research interests include telecommunications (mobile/broadband), VLSI design, and software engineering. His e-mail address is


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