A Definition of Legacy Systems Integration

Despite all the changes and "paradigm shifts" that have rocked the computing world over the past several decades, global enterprises still store the bulk of their data and process the majority of their transactions on mainframe-based systems such as VAX and S/390. These are tried-and-true systems that form the backbone of a typical organization's business processes and transactions.

These systems are usually developed in COBOL or another obscure language and are built as independent batch-oriented systems using proprietary data storage and communications protocols. The UI is usually complex, heavily loaded, and character-based. Business logic, data access logic, presentation services, and control flow are typically mixed within the confines of individual monolithic programs. Finally, access to the data is often limited and only possible through proprietary means.

You should realize that the term "legacy" is by no means restricted to the mainframe-based systems or other systems that have developed since the onset of Web-based applications. As technologies relentlessly move forward, you will always have systems that were not developed using the latest tools, languages, and protocols. For example, in our Internet-centric world of IP and XML, even relatively recent technologies such as Visual Basic and PC LAN-based client/server systems can be considered legacy systems. Of course, to some companies these solutions are no less valuable than the mainframe-based systems.

In a perfect world companies would rewrite legacy applications to be Web enabled. Such projects, however, can take months or years, so companies are not about to throw out the legacy applications currently running their businesses. Therefore, few projects have the benefit of being able to start from scratch. Instead, most development teams need to take into account existing legacy systems when they're developing new applications. This is known as "legacy systems integration," and a whole industry has grown around it.