Object persistence in object-oriented applications

Object-oriented models have rapidly become the model of choice for programming most new computer applications. Since most application programs need to deal with persistent data, adding persistence to objects is essential to making object-oriented applications useful in practice. There are three classes of solutions for implementing persistence in object-oriented applications: the gateway-based object persistence approach, which involves adding object-oriented programming access to persistent data stored using traditional non-object-oriented data stores, the object-relational database management system (DBMS) approach, which involves enhancing the extremely popular relational data model by adding object-oriented modeling features, and the object-oriented DBMS approach (also called the persistent programming language approach), which involves adding persistence support to objects in an object-oriented programming language. In this paper, we describe the major characteristics and requirements of object-oriented applications and how they may affect the choice of a system and method for making objects persistent in that application. We discuss the user and programming interfaces provided by various products and tools for object-oriented applications that create and manipulate persistent objects. In addition, we describe the pros and cons of choosing a particular mechanism for making objects persistent, including implementation requirements and limitations imposed by each of the three approaches to object persistence previously mentioned. Given that several object-oriented applications might need to share the same data, we describe how such applications can interoperate with each other. Finally, we describe the problems and solutions of how object-oriented applications can coexist with non-object-oriented (legacy) applications that access the same data.