nd deletion of their component objects. That means that the database language should be extended in a way that these operators will be included.The identity of an object is what makes it different from all the other objects. This allows the objects to be independent of their values. Therefore the notion of identical objects is introduced: two objects are equal if they have the same values, but are identical if they have the same object identity. The fact that each object possesses an identity facilitates the handling of composite objects since it makes the common use of objects possible and it protects the consistency of the database. If a component object is changed, this change affects all the composite objects that reference it. Due to the object identity, there is no need for replicates, and that is how the consistency of the database is protected.The mechanism of encapsulation allows the hiding of the internal state of the objects. The internal state of an object is not liable to direct access. It can only be accessed by its methods. Objects that have this ability are called encapsulated objects. There are many types of encapsulation including: full, write, and partial. Using full encapsulation, all the operations on objects are done via message sending and method execution. In write encapsulation, the internal state of the objects is visible only for reading operations. Partial encapsulation involves allowing direct access for reading and writing for only a part of the internal state (private and public part). The use of the same message for different methods that belong to different classes can facilitate the design of the database as well as of the applications that access it.In general, since the internal structure of an object is not visible by the other objects, we can assign to methods with the same functionality the same message even if their implementation is different. This is called overloading of the m...
