Enterprise JavaBeans, Second Edition

Primary Services

There are many value-added services available for distributed applications. The OMG (the CORBA governing body), for example, has defined 13 of these services for use in CORBA-compliant ORBs. This book looks at six value-added services that are called the primary services, because they are required to create an effective CTM. The primary services include concurrency, transactions, persistence, distributed objects, naming, and security.

The six primary services are not new concepts; the OMG defined interfaces for a most of them in CORBA some time ago. In most traditional CORBA ORBs, services are add-on subsystems that are explicitly utilized by the application code. This means that the server-side component developer has to write code to use primary service APIs right alongside their business logic. The use of primary services becomes complicated when they are used in combination with resource management techniques because the primary services are themselves complex. Using them in combination only compounds the problem.

As more complex component interactions are discovered, coordinating these services becomes a difficult task, requiring system-level expertise unrelated to the task of writing the application’s business logic. Application developers can become so mired in the system-level concerns of coordinating various primary services and resource management mechanisms that their main responsibility, modeling the business, is all but forgotten.

EJB servers automatically ...