racteristics that can stand as the set of specification requirements for the construction of such a system. These should also be used as the set of features that one has to check in order to find out if a system is really an OODBMS. The features of the OODBMS can be divided as follows:•mandatory features: these are the features that one system should have in order to deserve the title OODBMS.•optional features: these are the features that if one system has, should be considered better than another that does not have them, provided that both have all the mandatory features.•open choices: these are features that a designer of a system can choose if and how to implement. They represent the degrees of freedom left to the system designers.An OODBMS should be a database management system and at the same time an object oriented system. The first characteristic is translated to the following features: persistence, concurrency, recovery, secondary storage management, and ad hoc query mechanisms. The second characteristic is translated to the following: composite objects, object-identity, encapsulation, inheritance overriding and late binding, extensibility, and computational completeness of the database language used.Composite objects can be built recursively from simpler ones by applying constructors to them. These simpler objects can be integers, characters, strings, booleans, and in general objects of types that all the programming languages possess. There are various constructors such as list, set, bag, array, tuple, etc. The minimal set of constructors that a system must have is: set (to represent unordered collections of real world objects), list (to represent ordered collections of real world objects), tuple (to represent properties of real world objects). A system that supports composite objects and therefore constructors for their building, should also support operators for the retrieval, insertion, a...
