Data mining and rough set theory

Class Hierarchies, Factories, and Stable Designs Much of the debate about the general aptness of class hierarchies is rooted in the different objectives taxonomists and implementers are thought to pursue. Designers of conceptual hierarchies tend to embrace Aristotle’s principle of genus et differentiae leading to a taxonomic hierarchy of categories or types [7], while those with implementation in mind focus on the reuse of class definitions and polymorphism as made possible by subclassing and inheritance. This has led to an extensive discussion (see [1, 4, 5, 8]) as to whether Square should be a subclass of Rectangle or vice versa, a dilemma that is, of course, precedential in character. Despite the different perspectives there appears to be a broad consensus that, in principle at least, • both a conceptual type and a class (as a programming construct) are intensions the extensions of which are sets of instances; and • the extensions of subtypes are subsets of the extensions of