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+4 votes

Consider the following Relationship Entity Diagram(ERP)

Which of the following possible relations will not hold if the above ERD is mapped into a relation model?

  1. Person (NID, Name)
  2. Qualification (NIDExamID, QualifiedDate)
  3. Exam (ExamIDNID, ExamName)
  4. Exam (ExamID, ExamName)
in Databases by Veteran (106k points) | 2.4k views

3 Answers

+10 votes
Best answer

If we have to convert an ER -Diagram into Relational model then 

we can create one table for each entity .In this way we are going to get one table for Entity Person and one table for Entity Exam.we can't avoid these 2 Tables .

Now problem is with relationship Entity on which side should we add it unfortunately we can't add it on either side so we have to create a new table in which we are going to take Primary key of Entity Person and Primary key of Entity Exam .So in this way we can represents the relationship .

So option A ,B and D seems okay but Option C does not make any sense .Why do we need this if we have already represented all our Entity . 

by Boss (45.4k points)
selected by
Well your explanation is right but in option "A" when we create a single table for entity "PERSON" which has NID as key it has been not mentioned NID as a key there is no underlined in NID part
0 votes
Answer- C
by Loyal (10k points)
0 votes

NID can't uniquely identify the attributes of Exam table, hence Option C.

by Loyal (7k points)

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