Discussion
In an Entity-Relationship (ER) model, suppose \(R\) is a many-to-one relationship from entity set E1 to entity set E2. Assume that E1 and E2 participate totally in \(R\) and that the cardinality of E1 is greater than the cardinality of E2.
Which one of the following is true about \(R\)?
Answer: A
The true statement is Every entity in E1 is associated with exactly one entity in E2.
Many-to-one from E1 to E2 means each E1 entity is related to at most one E2 entity. Total participation of E1 means each E1 entity is related to at least one. Together, each E1 entity has exactly one partner in E2.
Some entity in E1 with more than one E2 partner would break the many-to-one rule. On the E2 side, E1 has more entities than E2 and every E1 entity is mapped to some E2 entity, so by the pigeonhole principle some E2 entity is related to two or more E1 entities. That rules out 'exactly one' and 'at most one' for E2.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development