Consider the E-R diagram below

Which entity or entities will have foreign key(s)?

Question

Consider the E-R diagram below

Which entity or entities will have foreign key(s)?

BlackTom AI · Accepted Answer

A one-to-one / one-to-many cardinality and participation interpretation determines where foreign keys appear.

Relevant concepts:
- A foreign key (FK) is placed in the table on the “many” side of a one-to-many relationship or on either/both sides of a one-to-one depending on total participation and design choices.
- Cardinality symbols: a crow’s foot indicates “many”; a single bar indicates “one” (total participation); double bars often indicate mandatory participation/identifying relationships.

Step-by-step reasoning:
1. Inspect the LoyaltyProgram—Membership link: the diagram shows a crow’s foot at the Membership end and a single bar at the LoyaltyProgram end. That means one LoyaltyProgram can have many Membership records. Therefore Membership must carry a foreign key referencing LoyaltyProgram (e.g., AirlineName as FK in Membership). This is standard: the “many” side stores the FK to the “one” side.
2. Inspect the Membership—Customer link: the relationship exhibits an identifying/mandatory style (the diagram markings indicate tight/mandatory participation between these two). That implies the relationship is effectively one-to-one (or one-to-zero/one with mandatory participation). In such cases the FK can be placed in either table; when both sides show total/mandatory participation or the model requires quick lookup in both directions, designers may include FKs on both entities or use a shared primary key. The diagram’s participation markers indicate Customer is dependent on Membership and Membership is closely tied to Customer, so Customer will include a foreign key referencing Membership (for example Customer.CustomerID or Customer.MembershipID depending on design). Meanwhile Membership already had the FK to LoyaltyProgram.
3. Summarize FKs: Membership contains a FK to LoyaltyProgram; Customer contains a FK to Membership (given the shown total/identifying participation). Thus both Customer and Membership tables will have foreign keys.

Why other choices are incorrect:
- “Membership” alone ignores the FK needed on Customer because of the mandatory/identifying relationship.
- “LoyaltyProgram” alone is wrong: LoyaltyProgram is the parent (one side) and does not need a FK.
- “Both LoyaltyProgram and Membership” is wrong because LoyaltyProgram, as the one side, need not store an FK to Membership.
- “Each entity will have at least one foreign key” is wrong because LoyaltyProgram does not.
- “Customer” alone is wrong because Membership also needs a FK to LoyaltyProgram.

Conclusion: Both Customer and Membership will have foreign keys, which matches the provided answer.

Consider the E-R diagram below Which entity or entities will have foreign key(s)?单项选择题

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