ITPEC FE Subject A April 2025 Question 20
Topic: DatabasesAlso asked in October 2020
In the UML data model shown in the figure below, which of the following is a multiplicity that should be inserted in blanks I and II?
[Conditions]
(1)One or more employees belong to a department.(2)An employee belongs to any one department.(3)The history of the departments to which an employee has belonged is recorded as the assignment history.
Explanation
One or more in both blanks — every department and every employee has at least one assignment history record, so I and II are both 1..
- •Blank I, records per department: by condition (1) a department always has at least one employee, and each belonging is recorded, so one or more records
- •Blank II, records per employee: by condition (2) every employee belongs to a department, so at least the current assignment is recorded, and by condition (3) past departments add more records, so one or more
- •The fixed 1s: each assignment history record refers to exactly one department and one employee
Answer (d)
Why not others:
- •(a) —
0.in both blanks allows a department with no employees and an employee with no department, breaking conditions (1) and (2).* - •(b) —
0.in blank I allows a department with no members, contradicting condition (1).* - •(c) —
0.in blank II allows an employee who belongs to no department, contradicting condition (2).*
Key rule: The lower bound of a multiplicity comes from the "must" rules (mandatory gives 1, optional gives 0); the upper bound comes from whether several links, such as a history, are allowed.
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