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Related Topics: Java EE Journal, SOA & WOA Magazine

J2EE Journal: Article

Towards Legacy Enablement Using SOA and Web Services

Leverage legacy systems with SOA

Care should be taken while selecting the adapter and its version, so that it is compatible with the existing hardware and software. Once the product is procured and installed, proper testing should be done before using it for the application integration. The following diagram illustrates the components involved in the JCA-based solution.

Pros and Cons of the Adapter-Based Approach
There are several advantages of using the adapter-based approach for legacy enablement:

  • Once the installation and configuration is done, the time to market for applications that can interact with the legacy component is very low
  • It is easy for the developers to use the adapters because they just need to create a simple call similar to invoking a Java class
  • It does not require any changes to the existing legacy applications
  • It provides a bidirectional interaction with the legacy applications so that we may also use any front-end component from the legacy applications
  • It is easy to use because it hides all of the complexity involved in marshalling and demarshalling requests to and from legacy applications
  • This model can be easily scaled up by adding more adapters for load sharing
Although there are significant benefits to using JCA adapters for legacy enablement, these adapters have some shortcomings that may be problematic in certain situations:
  • All of the adapters are tightly coupled with the applications
  • Configuring adapters may be a difficult task that may require help from the system administrator for the legacy platform.
  • Configuration is a time-consuming process because each function on the legacy system that has to be used by the front end needs to be separately configured
  • Configuring application parameters can be difficult when the legacy application involved is complex
  • There is no control over how the messages get transferred from the front end to legacy and vice versa
  • It is not cost effective because the adapters are typically expensive
  • Maintaining large number of such adapters on an enterprise level is difficult and time consuming
Some of the vendors in this space are: Web Service-Based Legacy Enablement Using Microsoft Host Integration Server 2004
Microsoft Host Integration Server 2004 helps to integrate IBM host applications, data sources, messaging, and security systems with new solutions developed using the Microsoft Windows Server System platform. This option may be useful for companies that are interested in using a Microsoft-centric architecture without reliance on the external tools discussed above.

The Host Integration Server 2004 features include network integration, host access with enhanced security, and application integration that enables Windows developers to publish business processes in IBM mainframe and AS/400 applications as XML Web services, which brings their Host applications and processes into a services-oriented environment. Figure 6 illustrates the overall architecture for the solution using Microsoft Host Integration Server. The following are some key features of this product:

  • Host Integration Server 2004's new Visual Studio integration piece allows us to take logic from a mainframe and expose it as a Web service from a Windows Server machine. That means we can now take legacy CICS and Information Management System (IMS) mainframe applications, publish them as Web services, and thus open it to the rest of the world or to business partners without virtually even touching the legacy application. Host Integration Server 2004 integrates with the Microsoft Visual Studio 2003, which gives it a much better look and feel.
  • Microsoft has upgraded the COM-based transaction coordinator to the new .NET-based Transaction Integrator (TI). This helps to add XML Web services capabilities to legacy applications.
  • Microsoft Message Queue Services (MSMQ) MQSeries Bridge lets administrators more easily link transactional applications running on different platforms, thereby creating an interplatform message-queuing capability. The Host Integration Server feature supports MSMQ 2.0 and MQSeries 5.1.
  • Host Integration Server 2004 offers a service that lets SNA-based applications running on IBM mainframes interoperate with Host Integration Server 2004 over IP-based networks. The Host Integration Server service will let enterprises replace legacy-networking hardware with standard Gigabit Ethernet networking hardware, thus saving money and improving performance.
  • Host Integration Server 2004 has a functionality called Windows-Initiated Processing (WIP) that helps to call applications residing on the mainframe. Another new feature that has been added to Host Integration 2004 is Host Initiated Processing (HIP), which answers many of the WIP's limitations. Now the mainframe applications can act as clients and call other applications residing on a mainframe or a Windows Server machine. On the Windows end, Microsoft supplies listener services to make the Host Integration Server functionality work. These services use the same message formats that mainframes use and behave identically to mainframe applications. Thus, a Windows box can act as a peer to a mainframe.
  • Enterprise Single Sign-On: Enterprise Single Sign-On services (SSO) have been enhanced to provide end users with a single sign-on experience when accessing non-Windows applications on mainframes and AS/400 systems. Enterprise SSO streamlines and reduces the management burden by automatically and simultaneously authenticating a user on both the Windows Server System and on the IBM host system. Enterprise SSO maps Active Directory-based domain accounts to non-Windows user credentials systems, such as RACF credentials in a credential database.
  • The Host Integration Server development environment now runs from within Visual Studio .NET 2003. Programmers can use standard Visual Basic .NET or C# code, for example, to write applications that exchange data with mainframes. Host Integration Server also has a Microsoft Management Console (MMC)-based administration tool for deploying these applications, which lets you take advantage ofthe native capabilities of Windows Server-based machines, including load balancing and clustering.
  • XML and Two-Phase Commit Support: the new Host Integration Server 2004 TI allows Windows developers to publish business processes found in mainframe CICS and IMS applications, as well as those found in IBM AS/400 systems as .NET assemblies or XML Web services, also referred to as Windows-Initiated Processing.
  • .NET Framework Support: A common design environment for faster development cycles using Microsoft Visual Studio .NET. The TI Project type includes multiple views (host, COM, .NET) as well as import/export wizards for COBOL and RPG host source code. Developers derive the benefits of object-oriented, distributed applications, including rapid development, managed code, and simpler maintenance.
  • Remote Diagnostics: The Host Integration Server 2004 Diagnostics tool has been improved to allow the administrator to test and troubleshoot SNA connections and resources from a central location.
  • Easy DB2 Access: Host Integration Server 2004 offers a new central Data Access Tool for creating and managing connection definitions to DB2 and host file systems, and a DB2 Connect Import Wizard to define data source definitions for use with Microsoft DB2 data providers.
  • Data Interoperability: Host Integration Server 2004 ships with standard ODBC, OLE DB, and .NET drivers for DB2, allowing programmers to access DB2 databases in the same manner they access other Windows-based databases. Microsoft has enhanced the DB2 network protocol client to support two-phase commit (2PC) for IP-based distributed transactions.
In this article we have examined the pain points associated with legacy systems as well as a variety of options to tackle the issues by using integration techniques. We have looked at J2EE-based techniques using JCA adapters, integration using the Microsoft Host Integration Server, as well as Web service-based integration using tools such as Shadow z/Services from NEON Systems. Based on the flexibility and openness provided by SOA, we recommend the use of Web services to integrate business applications with existing legacy applications. We would like to suggest this option as a first step even for situations where the legacy platform has a medium- or long-term decommissioning strategy in place. SOA-based legacy enablement can provide the loose coupling and platform independence that can free component developers from the constraints of legacy platforms.


More Stories By Sriram Anand

Dr. Sriram Anand is a principal researcher at Infosys Technologies, Bangalore. Prior to joining Infosys he worked in IT consulting as well as product engineering in the US for over 12 years. His interests include enterprise architecture, service-oriented architecture, and legacy integration and software engineering methodologies. Dr. Anand is experienced in designing enterprise architectural strategy for leading U.S. companies in the financial services, retail, and pharmaceutical domains. He holds a Bachelor?s degree from IIT-Madras with a PhD from SUNY-Buffalo, USA.

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