UGC-NET | UGC NET CS 2018 July – II | Question 67
A many-to-one relationship exists between entity sets r 1 and r 2 . How will it be represented using functional depedencies if Pk(r) denotes the primary key attribute of relation r ?
(A) Pk(r1 ) → Pk(r 2)
(B) Pk(r2 ) → Pk(r 1 )
(C) Pk(r2 ) → Pk(r1 ) and Pk(r 1 ) → Pk(r 2 )
(D) Pk(r 2 ) → Pk(r1 ) or Pk(r 1 ) → Pk(r 2)
Explanation: A many to one relationship set exists between entity sets Employee and Department.
Let two relations R1(employee with pk empId)
R2(Department with pk DId)
Here, empId can uniquely identify DId but DId can not uniquely identify the empId.
Hence, pk(R1) -> pk(R2)