Wrapping an Application
Another approach to get the mainframe application from the distributed environment is to wrap the old interface by installing new software components. For example, IBM MVS, the Microsoft products COMT1 wraps CICS transactions with COM+. There are similar products for Enterprise Java Beans. The wrapping is not difficult, but the catch is that the application on the mainframe transaction monitor is stateless. In most cases, it is inevitable because there is no terminal attached to the web application session, and because the web session is so different from a terminal session, all the baggage that comes with a terminal interface must be eliminated. So the key question is how complex you want to make this wrapping. Should it be minimum wrapping, simply converting old technology to new technology with minimum overhead, or should it be creating new object components where you want to make these objects reusable across the enterprise?
The second approach is advocated by Microsoft DNA and Sun J2EE three-tier architectures. In both architectures, the transaction logic implemented on the mainframe is part of the data link layer, in contrast to the transaction logic implemented in COM+ or EJB, which is a part of the middle tier. Sharing business logic developed in business objects using these architectures increases the likelihood of the reuse of objects across enterprise for different presentation channels. Sometimes the logic in business object components becomes more complex. For example, the data you want to expose in business object components may be physically located in several back-end transaction systems.
Another example is to make a batch system look like an online system by storing a local copy of the data that is more up-to-date than the back-end system. This is called pseudo updating. When you face difficulties such as these, you have to decide whether you want to add complex code in the business object or whether it is better to fix up the back-end system to be more supportive of the new functionality. The disadvantage of creating business object components is that they need to be designed with care. Therefore, having any common middleware such as MQSeries or Tuxedo seems more of an important factor for success than having an object foundation. However, it might be too early to judge because most of the experience with multiple presentation channels is new, and it is hard to tell how truly flexible and effective a solution is until sometime in the future.