The following is a graphical representation of two entity sets in a system for a building with access controlled entrance.

Which of the following statements best describes the relationship between Visitor and Visitor Pass?

Question

The following is a graphical representation of two entity sets in a system for a building with access controlled entrance.

Which of the following statements best describes the relationship between Visitor and Visitor Pass?

BlackTom AI · Accepted Answer

The diagram represents a one-to-one, mandatory relationship: every Visitor is paired with exactly one Visitor Pass, and every Visitor Pass is allocated to exactly one Visitor.

Relevant concepts:
- Cardinality specifies how many instances of one entity relate to a single instance of another (one-to-one, one-to-many, many-to-many).
- Participation (mandatory vs optional) indicates whether an entity instance must participate in the relationship (minimum cardinality 1 means mandatory).
- In simple ER-style pictorials, a single line from each instance to exactly one counterpart indicates exactly-one association on both sides.

Step‑by‑step reasoning:
1. Inspect the lines connecting individual Visitor instances (left) to Visitor Pass instances (right). Each Visitor instance has exactly one line to a single Visitor Pass instance — this means a Visitor cannot have zero or more than one Pass (minimum 1, maximum 1).
2. Inspect the lines arriving at each Visitor Pass instance. Each Pass is connected from exactly one Visitor instance — this means a Pass cannot be unassigned (zero) nor shared among multiple Visitors (maximum 1).
3. Combining these observations yields the cardinality pair (1,1) for both sides: one Visitor ↔ one Visitor Pass, and vice versa. That is the definition of a one-to-one mandatory relationship.

Why the correct option is correct:
- It states both sides are required and unique: "one and only one pass" per Visitor and "one and only one visitor" per Pass, matching the (1,1) interpretation above.

Why the other options are incorrect:
- Option 2 allows a Pass to be unassigned (optional) — contradicts the observed mandatory assignment.
- Option 3 only says "at least one pass" for a Visitor (allows multiple passes) and omits Pass-to-Visitor constraints.
- Option 4 allows multiple passes per Visitor (one-to-many) — contradicts the one-to-one mapping seen.

Final confirmation: The correct answer is "A visitor must have one and only one pass and each pass must be allocated to one and only one visitor," which matches the provided answer.

The following is a graphical representation of two entity sets in a system for a building with access controlled entrance. Which of the following statements best describes the relationship between Visitor and Visitor Pass? 单项选择题

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