In an ER model, suppose R is a many-to-one relationship from entity set E1 to entity set E2. Both E1

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Question

In an ER model, suppose R is a many-to-one relationship from entity set E1 to entity set E2. Both E1 and E2 participate totally in R, and |E1| > |E2|. Which one of the following is true about R?

Accepted Answer

Correct Answer: A — Every entity in E1 is associated with exactly one entity in E2Step-by-step Solution:Many-to-one from E1 to E2 means each entity in E1 is associated with at most one entity in E2 (E2 is on the "one" side). This is the structural constraint imposed by the relationship type.Total participation of E1 means every entity in E1 must participate in at least one instance of R.Combining both constraints: each E1 entity participates in at least one relationship (total participation) and in at most one relationship (many-to-one). Therefore, every entity in E1 participates in exactly one relationship instance and is associated with exactly one entity in E2.Why the other options are incorrect:Option B — Many-to-one explicitly forbids any E1 entity from being associated with more than one E2 entity. The relationship maps each E1 entity to at most one E2 entity.Option C — "Every entity in E2 is associated with exactly one entity in E1" would imply a one-to-one relationship. Since |E1| > |E2| and all of E1 participates, at least one E2 entity must be associated with multiple E1 entities (by the pigeonhole principle). Therefore, this cannot hold for all E2 entities.Option D — "At most one" for E2 would similarly be violated by the pigeonhole principle: |E1| > |E2| entities all mapping into E2, so some E2 entity must receive more than one E1 entity.Key Concept: In a many-to-one relationship from E1 to E2, each E1 entity maps to at most one E2 entity. When E1 also participates totally, every E1 entity maps to exactly one E2 entity. The "many" side refers to E1 (multiple E1 entities can map to the same E2 entity), while the "one" side refers to E2 (each E1 entity maps to at most one E2 entity).

In an ER model, suppose R is a many-to-one relationship from entity set E1 to entity set E2. Both E1 and E2 participate totally in R, and |E1| > |E2|. Which one of the following is true about R?

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In an ER model, suppose R is a many-to-one relationship from entity set E1 to entity set E2. Both E1 and E2 participate totally in R, and |E1| > |E2|. Which one of the following is true about R?

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