Using Application Server To Support Online Evolution

The online evolution of application depends highly on its runtime environment. This paper addresses how to support applications that execute on application servers that compose of component containers and common services. From the requirement’s viewpoint, evolution of software can be divided into four categories: evolution that does not alter requirements, evolution that alters functional requirements, evolution that alters local constrain requirements, and evolution that alters global constrain requirements. All changes at the requirements level can be mapped to changes at the implementation level. Using our approach, implementation level entities, components and interceptors, are responsible for online evolution. Evolution includes adding, removing, updating, and reconfiguring the entities. One key to our approach is to carefully distinguish states of component and interceptor, e.g., ready, active, executing and evolving. A well-designed architecture and feasible mechanisms for runtime instance loading are also keys to the solution. Based on this approach, an application server prototype, named PKUAS, has been implemented and is introduced in the end.