Despite the IT industry's obsession with the "next big thing," even valuable innovations are often put into context by legacy systems. Your bank account, mortgage, home and auto insurance, and pension are all likely to be running on a so-called legacy system.

They typically run a large portion of a company's critical business processes and contain years' worth of valuable coding and enhancements. While most of these systems are clearly getting the job done, they must evolve to continue to support the business in the most efficient manner.

As pressure mounts to access core functionality from the Web, integrate heterogeneous systems across the enterprise, comply with regulatory requirements or support new lines of business, legacy systems can no longer operate in isolated silos.

So, how can IT executives preserve mission-critical functionality while keeping pace with the latest and greatest in IT? There are three options that they typically consider:

• Rewrite - build a new system in a contemporary programming language to meet business requirements
• Package - purchase a new package that implements traditional core functionality
• Modernization - extend existing legacy systems to meet new requirements

There's no single correct answer as to which choice is correct. It can depend on the nature of the legacy system and the emergent business requirements - and in some cases, a combination of approaches may even be appropriate.

On the whole for a non-trivial enterprise system, the "rewrite" option would almost always represent the greatest risk and highest-cost approach. A rewrite is quite a different proposition to a "new write" of a completely fresh system that didn't previously exist. "Rip and Replace" involves spending considerable effort simply to replicate the functionality already available today. This approach requires a difficult combination of existing application and new technology knowledge. As we are all painfully aware, most large-scale projects of this kind will face challenges with timescales, cost, functionality, or performance.

A package, in contrast, will contain a core of proven functionality. However, a careful "gap analysis" of the package functionality and existing system functionality often reveals a need for significant extension in addition to a major new cost.

So, while both rewrites and packages have their place, in most scenarios the modernization and extension of an existing legacy system to meet new requirements will represent the fastest, most cost-effective and lowest-risk approach. The existing application can remain unchanged, meaning current business operations are not affected at all. As a result, the scope of the project can remain tightly defined to meet the new requirement at hand.
Modernization projects carry lower costs than a rewrite because they reuse critical business logic proven and evolved over many years. In addition, modernization makes use of the existing skills of mainframe programmers when pursuing new business requirements. It's important to draw on the expertise of these seasoned developers - much of which would be lost if legacy applications were disregarded.

Enter SOA
There's a dichotomy present in IT shops across the globe: preserve worker knowledge and application operations but embrace innovation, new technology, languages and delivery platforms. That's why one of a CIO's greatest priorities is to help his or her organization increase its market share and stay competitive by using the newer technologies - without sacrificing the benefits delivered by reliable legacy applications. In light of this, using Service Oriented Architecture (SOA) as a path to modernization is a major consideration for IT executives.

They take notice when they learn that, by migrating to a SOA through a Web Services environment, they can cut costs, reduce risk, and hasten time-to-market for new business initiatives. As such, making the move to SOA through reusable Web Services encapsulating legacy business processes represents a standards-based, strategic, and flexible way to modernize legacy applications.

The value and benefits of SOA are well publicized today but often in the context of new development. However, when applied to legacy systems SOA can become truly compelling. SOA frees a business process from the language in which it was written, as well as the platform it runs on - a powerful value proposition. This means that organizations can combine the value of proven business functionality with the agility of reusing services and the capabilities of .NET and other contemporary programming environments. Advantages of legacy transformation through SOA include:

• Improved agility through the reuse of existing business processes - any future compliance mandates or business needs can be addressed by reusing services previously updated, regardless of the platform or delivery
• Low-risk operations through consistency and reliance on proven business logic
• Reduced costs as middleware, software, and integration costs are lowered through the use of a single strategic architecture
• Improved time-to-market through rapid development enabled by reusing existing business processes in a standard SOA infrastructure

Put into Practice
Of course, with 200 billion lines of COBOL in production and legacy systems typically comprising tens of millions in lines of code, a complete infrastructure overhaul via SOA and Web Services would neither be practical or sensible. Most successful SOA initiatives are incremental, focusing on the business need and encapsulating the processes that present that business functionality as services. This approach can also force the discipline of actually defining, in isolation from the legacy system, the services that you'd like to create. In other words, the business need should define the strategic service framework rather than the legacy system simply replicating its existing interfaces as a potentially complex array of services.

Once the required services are defined, the areas in the legacy system that deliver this functionality must be identified. At this stage, a combination of application development knowledge and the use of program-understanding tools or solutions is highly recommended.

What follows is the heart of this whole process - the "unlocking" of legacy applications by leveraging their existing interfaces. Mainframe COBOL, CICS, and IMS systems have a variety of interfaces such as 3270 Data Flows, CICS COMMAREAs, and Screens that can be utilized. These are the way into the legacy code.

This is the stage where it becomes important to understand the new business need and the service definitions that best service this need. Rather than simply replicate the legacy interfaces, they should be aggregated and tailored to combine multiple transactions from the legacy system into the new business service.

Once this definition process is complete, this service can be deployed as an industry standard Web Service into .NET or a J2EE application server. Legacy functionality can now be accessed from a contemporary .NET user interface created and maintained using Visual Studio. Simply consumed as Web Services core business processes can be accessed from .NET languages, and integrated with new development under .NET or any other technology capable of consuming Web Services.

Benefits Unleashed
Beyond the obvious benefits of modernization, there are several underlying advantages to transforming legacy applications through SOA. By enabling enterprise systems to address new requirements or comply with new initiatives, and ensuring that these extensions don't alter or affect existing systems, valued functionality and intellectual property are retained. This precipitates a positive domino effect. It frees up time for businesses to focus efforts and resources on new projects, optimizes time-to-market for new products, and at the same time controls costs and reduces risk.

Another benefit of extending legacy systems to a SOA through Web Services is the ability for strategic business assets to be accessed at any time from any location. This makes cross-enterprise (or even extra-enterprise) integration a seamless process.

While IT decision makers should carefully evaluate the commitment to modernization through SOA, there are many positives to the approach. It is clear that SOA's strength lies in providing a standards-based infrastructure and a platform neutral way of delivering business services. The ability to retain the valuable functionality contained within legacy mainframe applications while at the same time defining and deploying services from them makes modernization virtually a "no brainer."

Ultimately, an SOA approach to application modernization is a low-risk, cost-effective path to ensuring that key enterprise systems evolve to best serve the business.