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Beginning Database Design by Clare Churcher

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CHAPTER 6Generalization and Specialization

As the data model begins to develop, situations will sometimes arise where we find that a class may not describe our possible objects as neatly as we might like. We might find that we have some objects for which some of the attributes do not really apply. For example, if we have a class to record information about all the people associated with a company, we might find that some have hourly pay rates while others have annual salaries. In many respects, much of the information about each of the employees is similar, but there are differences. We may also come across the case where we have started with two separate classes, for example Lecturers and Students, and then begin to realize that there is a ...

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