Object/Relational Mapping And Its Implementation In Java Environment

Object-oriented technology has been widely used in software engineering process including software analysis, design, programming and test. Like any other programming methods, to store and fetch data is the most important target for object-oriented programming. The effort to achieve the target for object-oriented programming is focused on persisting objects, and RDBMS is now the predominant storage mechanism to persist objects.Object-oriented programs' using RDBMS as their storage technology means you have to transfer data between the object-oriented view of a business model and the relational schema. Object-oriented model is based on some rationales of software engineering, whereas relational database schema is based sound mathematical rationales. The difference between the two foundations, which the object-oriented model and the rational database schema are based on, causes the imperfect fit between the two technologies, which is called "impedance mismatch". Because of the impedance mismatch between the two technologies, when using RDBMS to store persistent objects we must do the job called "Object/Relational Mapping". O/R mapping is such a process that tries to map the state of an object to the data in RDBMS in order to provide transparent persistent service. This thesis analyzes the rationale of O/R mapping focusing on the mapping taken between the Class with its instance and the tables in RDBMS.Many problems faced us when we try to carry out O/R mapping and the most difficult ones are how to represent unique identifiers, states (attributes), behaviours (methods) of objects and how to represent the classes in a hierarchy as well as complex relationship among objects. This thesis gives the strategy of O/R mapping to conquer these difficulties.Then this thesis introduces the many technologies for implementing O/R mapping in Java environment such as JDBC, Enterprise Entity Bean, JDO (Java Data Object) and third party O/R mapping tools. Also this thesis discusses the technologies in detail using a self-constructed criterion system and discusses how to choose one for a given project. At last a brief introduction to an application is given to show how to apply O/R mapping on J2EE platform.