Research And Application Of Multi-layer C/S Structure Based On CORBA

With the fantastic development of the network and database technology, and also with the augment of network-based services, the application system of the traditional two-layer Client/Server mode comes to show its limitations in efficiency, network safety, system upgrade ability and so on. It becomes necessary that a new software structure should come forth. So multi-layer system structure emerges.The dissertation focuses on the logical structure, realization technology and CORBA standard of multi-layer distributed database application system, and also focuses on the realization method of CORBA-based multi-layer database application system. The theory and realization method of some core technology in the multi-layer database application system have been discussed in this dissertation including load-balancing technology, fault-tolerance technology and session pooling technology etc.CORBA Visibroker provides a kind of random load-balancing algorithm. In order to improve the system's efficiency, a load-balancing algorithm based on the condition of database server's resource is addressed in the dissertation. According to the usage condition of the server's resources, the algorithm can allot the client request and balance the load in a more reasonable way.The function, faulty-tolerance of Visibroker, is realized by OsAgent. OsAgent provides the basic function of Naming Service and uses simple naming principle to maintain the directory of the objects. Through the communication with the CORBA server and the automatic detection of the running state of the COBRA server, OsAgent completes the search of COBRA objects thus provides the faulty-tolerance for client.Through the application of the Pooling technology, the article has constructed a Session Pool, which enables multi-users to share one connection to the database and saves the resource of the system and also improves the response speed of the system.Finally, the article has discussed a detailed application example--The developmentmethod of an on-line examination system of computer essential courses. This system is divided into three subsystems: a sign up subsystem, an examination subsystem and an examination management subsystem. The examination subsystem is the core system. In order to improve the efficiency, robustness and safety of the system it uses three-layer structure of the Client/Server mode, load-balancing technology, session pooling technology, faulty-tolerance technology and safety control.