Adding the Student Class to the Hierarchy
In order to have a more complete class hierarchy, we must take into account that a university has not only employees, but students as well. To add this, refer to the Workstudy View, which shows the attributes in the Student relational base table. From this, the Entry Date can be factored up into a Student Class as shown below. This introduces multiple inheritance to this object schema where the Workstudy class inherits attributes from both Teacher and Student. You should note that not all programming languages can support multiple inheritance. Nevertheless, it is important to understand the concept.
Yes, there are still redundant attributes in the Student and Employee classes. They will be addressed in the next step.
Next: Adding the Person Class to the hierarchy. Also see the related content below.
More on the general topic: Multi-Type Views
- Teacher View
- Employee View
- Creating Class Hierarchy by Factoring Attributes
- Adding the Person Class to the Hierarchy
- Object Schema for Relational Schema
Related Fact Book
Author: Douglas K Barry
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The Savvy Manager's Guide
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