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Modernizing Legacy Systems, part 1

Why modernize?

When I started working as a WebLogic consultant a couple of years ago, I systematically avoided projects with legacy systems integration. At the time, I was interested only in "pure" J2EE projects. The technology was very new and there was more than enough to do in order to help organizations adopt the J2EE/WebLogic platform as a viable solution for their e-business initiatives.

Today, J2EE has matured and the BEA WebLogic Platform has become an essential part of mission-critical applications in large organizations. But a new trend is also emerging: the need to integrate WebLogic with legacy systems in order to provide a unified, business process-centric IT environment. Moreover, organizations realize that in order to streamline their processes and provide value-added services to their customers, some critical business processes have to be "ported" or "re-hosted" from the legacy system to the WebLogic platform. This is what I call "modernizing" legacy systems. This series will discuss why the process of modernizing legacy systems is becoming an increasingly important business-driven requirement for organizations. I will present a step-by-step, incremental approach in order to minimize risks during the modernization effort. This article is an overview of the entire process and looks at why the modernization effort should be initiated. In part 2, I'll concentrate on integration and "re-hosting" patterns as well as building a common business domain model between the legacy system and the WebLogic platform. In part 3, I'll concentrate on the runtime and workflow aspects of the "modernized" platform.

Defining Modernization
Let's start by defining "modernizing" legacy systems and why such an effort should be initiated. First, what is a legacy system? I'm certain that the definition I'm going to give will make most Cobol programmers very unhappy! My perception of a legacy system is a software platform developed in a procedural language such as Cobol or RPG, hosted on a mainframe or an IBM iSeries. In most cases the maintenance costs of the system tend to increase over time while the available technical expertise around it decreases. Another way of defining a legacy system is the moment where the system cannot service new business requirements because of limitations such as technology and would therefore require modifications far beyond maintenance. However, most organizations have invested enormous amounts of intellectual property and money in these systems and expect to capitalize their return on investment, not counting that most of their mission-critical business processes run on them. So what is modernization? Modernization is the process of modifying a legacy system beyond maintenance in order to provide new added-value services such as enhanced reliability, flexibility, and security.

It is also worth mentioning here what modernization is not. It's not "revamping" or "screen-scraping," which consists mainly of replacing "green-screen" terminals with new presentation interfaces such as Web-enabled thin clients. Therefore, revamping affects presentation only. Modernization is also very different from "replacement," which is an effort to rebuild the system from scratch by a total code-rewrite process. Replacement may be an extremely risky process with a high chance of failure. In our case, the process of modernizing a legacy system involves the process of gradually "re-hosting" specific business processes initially written in Cobol to the BEA WebLogic Platform as J2EE components. The process is incremental and continuous, thus minimizing risks. Reasons why such an initiative could be desirable are:

  • Cobol is a procedural language ill-suited for today's enterprise-scale application developments. Therefore, the maintenance costs of legacy systems surpass the modernization costs.
  • Modernizing an existing legacy system is less costly and risky than completely replacing it because the process is less disruptive. Besides, organizations can continue to leverage their existing infrastructure during the effort.
  • The WebLogic Platform provides the essential building blocks for delivering component-based and service-oriented architectures, essential to today's e-business initiatives.
  • Tools such as BEA WebLogic Workshop enhance productivity far beyond the Cobol development environments.
  • The Java programming language and the J2EE platform, because of their component-based approach, promote software reuse and facilitate system maintenance in the medium to long term.
  • BEA WebLogic Server provides additional services such as scalability, security, and availability that would be hard to implement if created from scratch.
Modernization can take two approaches: in a black-box approach, we are not interested in understanding the inner workings of the legacy system. We simply use interfaces to the system and provide component wrappers to it. In a white-box approach, the inner workings of the legacy code are studied. For example, Cobol modules are examined in order to grasp the underlying business processes and rewrite them as EJB components. Often, the white-box approach might be required to provide true added value and move beyond enterprise application integration.

The Step-by-Step Approach
A modernization effort can span several years. During that time many factors, such as technology, can dramatically change. It is therefore essential to take a step-by-step, incremental approach towards modernizing legacy systems in order to minimize the risks of failure. In my experience, mostly in modernizing banking systems, I have found the following steps useful:

  • Build the business case
  • Understand the legacy system
  • Understand the value-added services provided by the WebLogic platform and define the target architecture
  • Prioritize use cases for porting business processes
  • Integrate the legacy system with the WebLogic platform
  • Port the business processes
Building the business case basically states the rationale and the reason why a modernization effort should be initiated over a less drastic change such as a maintenance effort. For example, for a back-office banking package, the business case could state that B2B business processes require the implementation of a WebLogic Server "front end" to the legacy system and some of the business processes such as portfolio management and straight-through processing should be re-hosted by the WebLogic platform. Basically it emphasizes that the return on investment for modernization will be higher than simply maintaining the legacy system.

Once the business case has been approved, the next step is to understand the legacy system's architecture. In our banking example, the legacy system consists of a two-tier architecture using "dumb" terminals for the presentation layer and modules written in Cobol hosted on an AS/400 encapsulating the business logic. At this point, after studying the system using a white-box approach, we might discover that some modifications are required in order to provide an integration path to the WebLogic Platform. For example, we might discover that some Cobol modules contain a mix of presentation logic and business logic. We could therefore "refactor" those modules as service programs (a service program is a special kind of Cobol module that can be easily encapsulated and called from Java code) in order to separate business logic from presentation logic. An important point to emphasize is that understanding the legacy system requires the knowledge and help of Cobol programmers and they should be included as stakeholders early in the process. Finally, this step results in a good understanding of the legacy system's architecture as well as possible ways of integrating the legacy system with the BEA WebLogic platform.

Leveraging value-added services provided by the WebLogic platform is usually easier because now we are in the realm of J2EE programming. The objective here is to define a component-based, service-oriented architecture for providing functional and nonfunctional services such as security and availability. However, the major task at this stage of the modernization process is to devise an architectural mapping between the two-tier legacy system and the WebLogic platform. For example, as illustrated in Figure 1, we might decide to build a five-tier architecture with the following tiers:

  • Client
  • Presentation
  • Business logic
  • Integration
  • Resource

 

The mapping process will then have to specify which modules of the legacy system will be mapped or "migrated" to specific tiers of the BEA WebLogic Platform as presentation-tier or business-tier components. This architectural transformation is actually a very critical step in the entire process. It has to achieve a certain number of goals, or qualities, in order to provide true added value to the modernization effort. The target architecture based on the WebLogic Platform should therefore have the following characteristics:

  • Service-oriented architecture
  • Component-based design
  • Layered architecture
A service-oriented architecture publishes discrete business functions and processes through discoverable interfaces. The processes can then be leveraged by other WebLogic applications or services as fundamental building blocks for higher-level services. Componentization and component-based design bring structure to the unstructured legacy Cobol code. Basically, it maps coarse-grained business processes as WebLogic hosted session or entity beans. The achieved added value is a higher level of code reuse as well as an interface-based "plug and play" architecture. Finally, the modernized architecture should be designed in layers where services are implemented on top of components that are in turn implemented using a common business domain class hierarchy.

The next step is to prioritize business processes - gathering a certain number of use cases identified in the legacy system by the project stakeholders as those with the most added value. They should become our initial candidates for the modernization process. In our banking example, the project stakeholders might decide that straight through processing provides enormous added value. They could therefore decide that the order-processing and account-management Cobol modules should be the first ones to be ported to the WebLogic platform as EJB components. At this point we have a development plan and we feel confident that we have identified the most valuable business processes of the legacy system to consider.

The next step is integration, which provides a way of having the legacy system and the modernized WebLogic platform "coexist" in a single, unified business platform. Once again, our objective is to take an incremental approach in order to minimize risks. We cannot afford to do a single "big-bang" replacement of the entire legacy system. Therefore, integration provides a pragmatic, intermediary step. During integration, we usually build adapters in order to "hide" the legacy system. For example we could use coarse-grained component wrappers implemented as EJBs in order to encapsulate the legacy system. Basically, the integration step provides the bridge between the legacy world and the WebLogic Platform. Integration should be transparent so that at any point in the effort, from an external perspective, the modernized WebLogic and legacy systems should provide a unified set of services, independent of their location. From a technical perspective, integration can be done by using different technologies such as JMS, SOAP/Web services, or JCA.

Finally, the last and longest step of the entire process, porting the business processes identified by project stakeholders and implementing them as EJB components, can be initiated. This componentization is a continuing effort and can be separated into two main aspects: code and data migration. The process of code migration consists of "re-creating" some equivalent functionality available in a legacy Cobol module and replacing it with its modernized EJB counterpart. If a whiteboard approach is used, the actual legacy code could be analyzed and the algorithm implemented inside it rewritten in Java as an EJB. In a blackboard approach, only the module's inputs and outputs are analyzed, in other words its functional interface, and a corresponding EJB with an equivalent interface is developed in Java. Both approaches are viable. For example, in a legacy banking system the whiteboard approach might be the only way to modernize an undocumented taxation module. Ever heard of the sentence "the code is the document"? In both cases the overall behavior of the legacy and modernized platforms should remain the same.

Data migration can be a bit trickier. Basically, data migration consists of modernizing the legacy database schema, perhaps because it has become unmanageable over time. For example, the original schema might be implemented using a DB2 database hosted on an AS400. It might be interesting for the modernized system to redesign the schema using entity beans and leveraging WebLogic's container-managed persistence services in a database-independent manner. Data migration can be done in two ways: data migration during code migration and data migration after code migration. Personally, for the sake of keeping a consistent behavior between the modernized WebLogic Platform and the legacy system, I recommend using a data-migration-after-code-migration approach. This will help keep the modernized and legacy systems consistent and in sync without requiring techniques such as data replication. If this approach is taken, then as mentioned under "integration," component wrappers should be used to encapsulate the legacy data.

Conclusion
This article introduced a step-by-step approach to modernizing legacy systems with the BEA WebLogic Platform. Modernization is the process of incrementally and continuously replacing specific modules of a legacy system developed in a procedural language such as Cobol or RPG by EJB components. The objectives of such an effort are to either provide additional business services going beyond maintenance of the legacy system or to leverage the services of the WebLogic Platform such as security, availability, and transaction processing. Modernization is a pragmatic approach in order to minimize risks and often has higher returns on investment than a complete replacement of the legacy system, which is also extremely risky. I have also mentioned some of the qualities, such as a service-oriented architecture and component - based platform, that the modernized architecture should exhibit in order to maximize reuse as well as return on investment.

This article provided a high-level overview of the entire process. In upcoming articles, I will delve into the details and show how to use specific tools such as BEA WebLogic Workshop to implement the different phases of the process.

More Stories By Anwar Ludin

Anwar Ludin specializes in service-oriented architectures for the financial sector. He currently works as an independent consultant for
financial institutions in Switzerland, where he helps design J2EE architectures based on the WebLogic platform.

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