| With the development of computer network technology, especially the development of Internet, an enterprise-level inter-OS and portable distributed multi-tiered database system is becoming into an important research direction in the range of database application.The dissertation strives to apply the newest development technology into the design of database model. Based on the idea of component and layer-designed method, and applying the newer distributed architecture-CORE A and object-oriented language-Java and J2EE, the paper designs the several database application models.There are three parts in the paper. The first is about the background of the paper and the research works of in-country and oversea people. The second part is the main part of the paper. It put forwards several new thoughts as communication middleware, servant middleware, and entity object etc., and designs several new multi-tiered database models. In the third part, an example is given. And the main research productions of the paper are summarized.The main work of the paper can be summarized as followings.In chapter one, the general two-tiered models and three-tiered models are analyzed. And the drawbacks of their extensibility, inter-OS, and portability, of these models are also discussed.In chapter two, the two popular distributed architectures-CORBA and COM/DCOM are compared. The limitation of COM/DCOM and the robust of CORBA are clarified. Then the mutual complementarities of the CORBA and Java are given. It is the prerequisite technology of the paper.In chapter three, based on the idea of middleware, the communication middleware (CM) and servant middleware (SM) design methods are put forward. By the stub, skeleton, ORB, and POA, the CM is designed, which solves the transparent communication between client and server. By implementing the IDL interface, the SM can connect the database and execute the business logic. It encapsulates the server implementation and forms as a middle layer between client and server. This method hides the safe logic of database and improves the safe performance.After the mapping between the servant object and relational database is studied, the CORBA middleware based four-tiered database application model is designed. The communication role is acted by CM, and the business role is acted by SM, which improves the extensibility, portability of general database models.The main work of chapter four is to construct the EJB based entity object and design the pure EJB entity object based database application model. Entity object is abstracted from database, and grant it some "behaviors". So the entity object acts as an intelligent object. It can be seen as a mirror of data object. By using data share pool, the entity object can share the connection to database, which improves the speed of data access, and solves the speed neck of general model.Based on EJB entity object and moving agent, a soft-component model is put. The movingagent is composed of object stub and home stub. It acts as a movable smart communication agent in the system, which solves the problem for client to locate the entity objects. The EJB entity object based multi-tiered database application model is designed. It applies the entity object as a agent for client to access the database. The model is a three-tiered and four-tiered co-existing model. The three-tiered part includes "Java client-EJB application server-RDBMS", and the four-tiered part includes ''Web browser梂eb server桬JB application server桼DBMS".Then, in chapter five, the integration of CORBA object and Java RMI/EJB object is studied. According to the difference of communication protocol between CORBA HOP and Java RMI JRMP, adopts RMI over HOP protocol to implement the inter-operation between them. Then analyzes the methods of the inter-operation of the two models of CORBA and Java RMI. Designs the RMI-IIOP protocol based model of the inter-operation between CORBA and EJB.Finally, an example is given. Based on the idea put by the paper, a project nam...
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