Generalization Of Object Identifiers And Class/subclass Hierarchies

Introduction: At first glance, it may seem impossible to generalize an object identifier. It remains unchanged even after structural reorganization of the data. However, since objects in an object-oriented database are organized into classes, which in turn are organized into class/subclass hierarchies, the generalization of an object can be performed by referring to its associated hierarchy. Thus, an object identifier can be generalized as follows.

First, the object identifier is generalized to the identifier of the lowest subclass to which the object belongs. The identifier of this subclass can then, in turn, be generalized to a higher level class/subclass identifier by climbing up the class/subclass hierarchy. Similarly, a class or a subclass can be generalized to its corresponding super class (es) by climbing up its associated class/subclass hierarchy.

“Can inherited properties of objects be generalized?” Since object-oriented databases are organized into class/subclass hierarchies, some attributes or methods of an object class are not explicitly specified in the class but are inherited from higher-level classes of the object. Some object-oriented database systems allow multiple inheritances, where properties can be inherited from more than one super class when the class/subclass “hierarchy” is organized in the shape of a lattice. The inherited properties of an object can be derived by query processing in the object-oriented database. From the data generalization point of view, it is unnecessary to distinguish which data are stored within the class and which are inherited from its super class. As long as the set of relevant data are collected by query processing, the data mining process will treat the inherited data in the same manner as the data stored in the object class, and perform generalization accordingly.

Methods are an important component of object-oriented databases. They can also be inherited by objects. Many behavioral data of objects can be derived by the application of methods. Since a method is usually defined by a computational procedure/function or by a set of deduction rules, it is impossible to perform generalization on the method itself. However, generalization can be performed on the data derived by application of the method. That is, once the set of task-relevant data is derived by application of the method, generalization can then be performed on these data.