There is a need to store the objects in a system persistent. This is often done by the help of a Database Management System (DBMS). Database specialization means that a DBMS product is integrated in the development of a system. The specialization of OOSE will vary according to the type of DBMS being used. The requirements model and analysis model can be studied for decisions about which objects are to be stored persistent. Since entity objects in the analysis model typically hold information that 'survives' a use case, the entity objects are major candidates for persistent storage. There is also a need to store other kinds of objects such as objects for handling interfaces etc.

The dominant type of DBMS used in industry today are relational databases (RDBMS). In such a databases, information is stored in tables. This causes a number of problems. First, the information in object-oriented systems are stored in objects. When using a RDBMS there is therefore a need to convert the object information structure into a table-oriented structure. This problem is sometimes referred to as the impedance problem. Another problem is that using a RDBMS creates a strong coupling between the application and the DBMS, and to make design minimally affected by the DBMS, as few parts of the system as possible should know about the DBMS' interface. A third problem is how to express inheritance in the database. The behavior of the objects need then to be handled by the programming language, and the data will be expressed in the database.

Generalization is the process of extracting shared characteristics from two or more classes, and combining them into a generalized