 processing. An OSS system supplier or an infrastructure provider often develops these component services and provides them as part of its software. For example, if J2EE architecture is being used, the EJB container provides these common infrastructure services. This re-use of infrastructure services allows rapid application development of open systems. 3.5.5 Integration between Components A next-generation OSS system is functional when all desired components are integrated together. Also to maximize and leverage the existing legacy OSS environment, the next-generation OSS components have to be integrated with the legacy systems. Integration can be achieved by two main mechanisms: tightly coupled or point-to-point, and loosely coupled or Chapter 8 - Next-Generation OSS message/middleware based. A loosely coupled messaging approach to integration allows more plug-and-play capability and allows implementation of multiple communication paradigms such as request/reply, publish/subscribe, notification, asynchronous and synchronous. A key concept in integrating legacy systems to next-generation OSS is "adapter components." An adapter component wraps the legacy system and presents the desired methods/functions through well-defined interface services, just like the other component. To other components of the next- generation OSS, the legacy system services can be accessed via the interface of the adapter component. The adapter component transforms the data model and communication protocol between the legacy and component world and can also bundle and aggregate discrete legacy system functions as business services in the component world. In Chapter 6 of this book, we have already described the challenges of integration and what approaches and methodologies can be used to best integrate OSS systems. Next-Generation Workflow Next-Generation Next-Generation OSS Component Component OSS Component OSS Component Message Bus Common Adapter Adapter Adapter Model Component Component Component Legacy Legacy Legacy Common Component S