f classification. Constrain inheritance: if class A is a subclass of class B, then any object of class A has thesame 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 anyinstance 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 Ais a subset of the set of instances of B.One of the necessary constituents of a DBMS is the data definition and manipulationlanguage (DDML), also called database language. The use of this language allows persistentdata to be created, updated, deleted, or retrieved. The database languages that were usedby the RDBMSs were based on the relational calculus or the relational algebra and hence werenot computationally complete although mathematically founded.An OODBMS should have a computationally complete database language because: it can beused 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 (impedancemismatch), and programmers do not need to learn another language if they choose to writetheir applications using this language.The designers of the OODBMSs that currently exist preferred to use as database languagessome of the most popular programming languages (C++, Smalltalk, Common Lisp, etc.) thancreating their own. In order to do this, however, they had to expand the semantics of thelanguage they chose in certain ways so that persistent data could be handled. Besides, if thelanguage chosen was not an object-oriented one, its semantics should be further expanded ina way that the object-oriented concepts could be included.Each database system comes with a set of predefined types (integer, real, char, string). Thisset should be extensible i.e. the user s...
