tance: if class A is a subclass of class B, then objects of A and B have the same internal structure although they may share the same methods and messages. This kind of inheritance corresponds to the notion of classification.•Constrain inheritance: if class A is a subclass of class B, then any object of class A has the same internal structure with any object of class B, but also satisfies a certain condition e.g. if "child" is a subclass of the class "person" and they share the attribute "age", then any instance of the class "child" must satisfy the condition its age to be less than 10.•Specialization inheritance: if class A is a subclass of class B, then the set of instances of A is a subset of the set of instances of B.One of the necessary constituents of a DBMS is the data definition and manipulation language (DDML), also called database language. The use of this language allows persistent data to be created, updated, deleted, or retrieved. The database languages that were used by the RDBMSs were based on the relational calculus or the relational algebra and hence were not computationally complete although mathematically founded.An OODBMS should have a computationally complete database language because: it can be used for the methods of the classes, for applications that are written in the same language, there is no need of transformation of the data structures or mapping of the data (impedance mismatch), and programmers do not need to learn another language if they choose to write their applications using this language.The designers of the OODBMSs that currently exist preferred to use as database languages some of the most popular programming languages (C++, Smalltalk, Common Lisp, etc.) than creating their own. In order to do this, however, they had to expand the semantics of the language they chose in certain ways so that persistent data could be handled. Besides, if the language chosen was not an object-orie...
