The object-oriented database paradigm is the combination of object-oriented programming language systems and persistent systems. The power of the OODB comes from the seamless treatment of both persistent data, as found in databases, and transient data, as found in executing programs.

Object oriented data base systems are the most recent development in data base technology. It is their goal to offer more complex data types in order to overcome the restrictions of, e.g., the normalization rules for relational data bases. In the context of object oriented data base models, an object consists of both its data and the operations (methods) which can be applied to the object. Each object is a concrete instance of an object class defining the attributes and operations of all its instances. Each instance has its unique identifier by which it can be referred to in the data base.

Object DBMSs add database functionality to object programming languages. They bring much more than persistent storage of programming language objects. Object DBMSs extend the semantics of the C++, Smalltalk and Java object programming languages to provide full-featured database programming capability, while retaining native language compatibility. A major benefit of this approach is the unification of the application and database development into a seamless data model and language environment. As a result, applications require less code, use more natural data modeling, and code bases are easier to maintain. Object developers can write complete database applications with a modest amount of additional effort

Following principles apply to object oriented data base models.

1. Inheritance

New object classes can be derived from another class (Witch called Super-class) by inheritance. The new classes inherit the attributes and methods of the super-class and offer additional attributes and operations. The relation between a derived class and its super-class is called ``isA" relation because an instance of the derived class also is an instance of the super-class.

2. Aggregation

Composite objects may be constructed as consisting of a set of elementary objects. The container object can communicate with its contained objects via their methods. The relation between the container object and its components is called "part of " relation because a component is a part of the container object.

3. Polymorphism

This feature is closely connected to inheritance. Derived classes may re-define methods of their super-classes. This is very useful for achieving class-specific behavior using messages already available for the super-class

4. Encapsulation

An object can only communicate with an object via messages. The operations provided by an object define the set of messages which can be understood by it; no other operations can be applied to an object.