Discussion
Let S be the specification: "Instructors teach courses. Students register for courses. Courses are allocated classrooms. Instructors guide students." Which one of the following ER diagrams CORRECTLY represents S?
- A.
- B.
- C.
- D.
Answer: D
The correct ER diagram is (iv).
The specification has four entity sets, Instructor, Course, Classroom and Student, and four relationships: Teaches (Instructor, Course), Registration (Student, Course), Allocation (Course, Classroom) and Guides (Instructor, Student). Diagram (iv) draws exactly these, with entities as rectangles and relationships as diamonds joining the right pairs.
Diagram (i) makes Registration an entity and Student a relationship. Diagram (ii) has no Student entity and has Guides linking Instructor to Projects. Diagram (iii) leaves Allocation unconnected to Classroom and joins Classroom directly to Course.
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