August 2009
Intermediate to advanced
893 pages
26h 48m
English
Content preview from Database Systems: Concepts, Design and Applications
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7.4. Categorisation
Categorisation is a process of modelling of a single subtype (or subclass) with a relationship that involves more than one distinct supertype (or superclass). Till now all the relationships that have been discussed, are a single distinct supertype. However, there could be need for modelling a single supertype/subtype relationship with more than one supertype, where the supertypes represent different entity set.
For example, let us assume that a vehicle is purchased in a company for transportation of goods from one department to another. Now, the owner of the vehicle can be a department, an employee or the company itself. This is a case of modelling a single supertype/subtype relationship with more than one supertype, where ...