ISRO | ISRO CS 2015 | Question 16

Consider the following Relationship Entity Diagram(ERD)

Which of the following possible relations will not hold if the above ERD is mapped into a relation model?
(A) Person (NID, Name)
(B) Qualification (NID, ExamID, QualifiedDate)
(C) Exam (ExamID, NID, ExamName)
(D) Exam (ExamID, ExamName)

Answer: (C)

Explanation: If we convert an ER diagram into relational model then we can create table for each entity.
We get two tables
One for Entity Person – Person(NID,Name)
One for Entity Exam – Exam(ExamID,ExamName)

Now for relationship Entity Qualification, we can not add QualifiedDate in any of the two tables formed so we need to create a new table using Primary Key from both Entity Person and Entity Exam.
We obtain Qualification(NID, ExamID, QualifiedDate)

Hence Option (C) does not make any sense.

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