By Jason Bloomberg and Ron Schmelzer

IT fads come and go, so-called paradigm shifts take place with annoying regularity, but legacy systems seem to stick around forever. What large company doesn’t have some important legacy application running on some aging piece of hardware, tucked away in their data center? Legacy comes in many forms: custom-coded applications with long-lost source code, unsupported packaged applications, or mainframe-based programs with proprietary interfaces. While these systems might be showing their age, there’s no arguing that they perform vital, often irreplaceable functions for the company. Legacy systems wouldn’t be such a cause for consternation, if it weren’t for the fact that so much business value resides on these systems—both in the form of essential data as well as critical business logic.

Nevertheless, business continues to require ever increasing levels of agility from the IT infrastructure. Competitive pressures, regulatory mandates and the unceasing search for greater business efficiency all drive IT to be better able to respond to a changing business environment. With every new technology endeavor, however, it seems that IT slips further away from meeting business imperatives. Something must be done! Rip and replace won’t work: It’s too expensive and risky. More middleware sure won’t help—who needs more glue for their glue? And simply throwing more applications or hardware at the problem isn’t going to solve anything—after all, the last thing we need is more legacy. What companies desperately need today is a new architectural approach for squeezing more value out of heterogeneous legacy resources, with enough agility to support an increasingly dynamic business environment. What companies need is service-oriented architecture.

Leveraging Legacy in SOA
Service-oriented architecture (SOA) attracts more than its fair share of hype. Such hype predictably leads to equal measure of anti-hype, which propounds that SOA paints a pretty picture, but once you roll up your sleeves and get into the dirty business of service-enabling legacy applications, you’ll find that the agility, reuse and efficiency benefits that SOA promises are forever out of reach, since services are simply interfaces to existing functionality. The truth, while less sensational, clearly lies between these two extremes.

In fact, there are three basic approaches for incorporating legacy applications into SOA implementations: accessing the data locked inside legacy systems directly, accessing business logic through APIs or other programmatic means, and emulating user interaction through terminal emulation, a.k.a. screen-scraping. As Joe Gentry, vice president of enterprise transaction systems at Software AG points out, “Legacy systems are still very prevalent. Today there are more than 200 billion lines of useful COBOL and other legacy code. Customers are looking for an adaptive approach for using legacy data directly, APIs, or going at screens.”