Consider the ER diagram in Figure 7.23. Assume that a course may or may not use a textbook, but that a text by definition is a book that is used in some course. A course may not use more than five books. Instructors teach from two to four courses. Supply (min, max) constraints on this diagram. State clearly any additional assumptions you make. If we add the relationship ADOPTS between INSTRUCTOR and TEXT, what (min, max) constraints would you put on it? Why?
What will be an ideal response?
Assuming the following additional assumptions:
- Each course is taught by exactly one instructor.
- Each textbook is used by one and only one course.
- An instructor does not have to adopt a textbook for all courses.
- If a text exists:
- ___it is used in some course,
- ___hence it is adopted by some instructor who teaches that course.
- An instructor is considered to adopt a text if it is used in some course taught
- by that instructor.
The resulting ER Diagram will have the (min, max) constraints shown in Figure B.
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