Topic: Database Management Systems
Let A and B be two entities in an E-R diagram with simple single value attributes. R1 and R2 are two relationships between M and N. R1 is one-to-many from A to B. R2 is many-to-many from A to B. What is the minimum number of tables required to represent A, B, R1 and R2 in the relational mode?
- A. 4
- B. 2
- C. 6
- D. 3
Answer: D. 3
Explanation: To represent the entities and relationships in a relational model:
1. Entity A requires 1 table.
2. Entity B requires 1 table.
3. Relationship R1 (1:N from A to B) can be mapped by adding the primary key of A as a foreign key in table B. It does not require a separate table.
4. Relationship R2 (M:N from A to B) requires a separate linking table containing the primary keys of both A and B as foreign keys.
Total minimum tables required = Table A + Table B + Table R2 = 3 tables.