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Can inherited properties of objects be generalized?
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 superclass (es) by climbing up its associated class/subclass hierarchy.
Because 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 superclass when the class/subclass “hierarchy” is organized in the shape of a lattice.
The inherited features of an object can be changed 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 superclass.
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 essential elements of object-oriented databases. They can also be inherited by objects.
Several behavioral data of objects can be changed by the application of methods. Because a method is generally represented by a computational process/function or by a set of deduction rules, it is impossible to perform generalization on the method itself. But, generalization can be implemented on the data derived by the application of the method. That is, once the set of task-relevant data is derived by the application of the method, generalization can then be performed on these data.
An attribute of an object can be composed of or defined by another object, some of whose attributes can be in turn composed of or represented by other objects, thus forming a class composition hierarchy. Generalization on a class composition hierarchy can be viewed as the generalization of a set of nested structured data(which are possibly infinite, if the nesting is recursive).
In an object database, data generalization and multidimensional analysis are not used for single objects but classes of objects. Since a set of objects in a class may share many attributes and methods, and the generalization of each attribute and method may apply a sequence of generalization operators, the major issue becomes how to develop the generalization processes cooperate between several attributes and methods in the classes.
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