Question-12

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 \(R\)?

• Every entity in \(E1\) is associated with exactly one entity in \(E2\).
• Some entity in \(E1\) is associated with more than one entity in \(E2\).
• Every entity in \(E2\) is associated with exactly one entity in \(E1\).
• Every entity in \(E2\) is associated with at most one entity in \(E1\).

Answer

• Every entity in \(E1\) is associated with exactly one entity in \(E2\).
• Some entity in \(E1\) is associated with more than one entity in \(E2\).
• Every entity in \(E2\) is associated with exactly one entity in \(E1\).
• Every entity in \(E2\) is associated with at most one entity in \(E1\).

Solution

Given that \(R\) is a many-to-one relationship from \(E1\) to \(E2\) and both \(E1\) and \(E2\) participate totally in \(R\), and the cardinality of \(E1\) is greater than the cardinality of \(E2\), the correct option is:

• Every entity in \(E1\) is associated with exactly one entity in \(E2\).

This aligns with the conditions of a many-to-one relationship where every entity in \(E1\) maps to exactly one entity in \(E2\), ensuring total participation and many-to-one from \(E1\) to \(E2\).