11.7. CERN's Experience
The EDH application has been running using an EJB-style component model since November 1998 (already old in terms of Java technology!). This design strategy has been extremely positive. The well-defined and relatively simple structure makes the architecture very effective for developing a variety of e-business applications.
CERN's experience with Oracle's EJB container has been reasonably successful. Although, the dream of complete application-server independence is tantalizingly close, most EJB containers still have some way to go before an application can be moved from one to another without modification.
Once the relatively minor incompatibilities have been resolved, application developers will be able to choose an application server based on factors such as performance, scalability, and maintenance tools.
11.7.1. Expensive Entities
In the EDH application, several entities (Currency, CatalogItem) could have been implemented as simple value objects, obtained from a session bean. It was possible to do this because they were simple.
It is important to remember that entity beans are relatively expensive in terms of resources, and they should be used only where the complicated machinery for authorization, transaction control, and persistence is necessary. Although the CatalogItem bean exists, it would not be a good choice for implementing the on-line catalog. When the user browses the catalog, the system should not have to create thousands of instances of the CatalogItem bean. Instead, a session bean should access the database directly. Only once the user had made a selection would a CatalogItem bean instance be created.
It would, of course, be preferable not to need this hybrid approach. In fact, the choice of when to use Entity Beans may eventually depend on the level of optimization of your EJB container. Hopefully, with time, the EJB specification will evolve to make this decision unnecessary (the EJB 2.0 specification does address this issue). In so doing, it will simplify application design and reduce the amount of code that needs to be aware of the actual database design.
11.7.2. Oracle EJE Accelerator
Currently, the Oracle EJE Accelerator has been available to application developers for only a short time. In recent tests, it was found that Oracle EJE Accelerator was two to three times faster at running the EDH application, compared with the previous fastest Java virtual machine (Symantec JIT).
The response time of any interactive application is a critical success factor, and using Oracle EJE Accelerator gives a significant advantage compared with EJB application servers relying on classical Java virtual machine technology.
11.7.3. Future Work
Although this is early in the life of EJB containers, EJBs appear to be an excellent way to develop highly scalable Java Web applications.
EDH is part of a larger set of AIS (Advanced Information System) applications that manage all corporate information at CERN, including financial, accounting, supplier, purchasing, materials management, HR, and payroll data. CERN aimed at acquiring 80 percent of the functionality through best-of-breed ERP suites in the various areas, all running Oracle on top of Sun servers. The remaining 20 percent was implemented at CERN for specific needs.
The integration and communication among the developed and acquired software modules is currently achieved with a foundation layer, which consists of a set of database tables with an extensive interface through stored procedures. The aim is to rearchitect this layer on top of the EJB component framework in which all business objects are truly unique and have a well-defined interface to the outside world. Areas such as portals, wireless, business intelligence, dynamic Web services, collaboration, and process integration are already part of the Oracle9iAS infrastructure. This would greatly simplify integration of enterprise components and prepare the EDH application for use on any wireless or mobile device.
For more information about Java technology and Oracle, visit http://otn.oracle.com/tech/java/. For more information about the Oracle application server, visit http://www.oracle.com/ip/deploy/ias/index.html. For more information about CERN, visit http://www.cern.ch.