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GATE 2018 CS – Question 21

Databases · ER-Model and Database Architecture · 1 mark · Multiple choice

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 $R$?

  1. Every entity in E1 is associated with exactly one entity in E2.
  2. Some entity in E1 is associated with more than one entity in E2.
  3. Every entity in E2 is associated with exactly one entity in E1.
  4. Every entity in E2 is associated with at most one entity in E1.

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Show answer and explanation

Correct answer: (A) Every entity in E1 is associated with exactly one entity in E2.

Explanation

Many-to-one with total participation of E1 means every entity in E1 maps to exactly one entity in E2. Since $|E1|>|E2|$, some E2 entity is used by several E1 entities, so C and D fail.