Question at position 28 In the figure below, what is depicted? A one-to-many relationshipA unary relationshipA one-to-one relationshipAn associative entity

Question

BlackTom AI · Accepted Answer

A unary (recursive) relationship is when an entity type has a relationship with itself — the same entity participates on both sides of the relationship.

Relevant concepts:
- Unary (recursive) relationship: one entity type is related to itself (e.g., Employee supervises Employee). It is normally drawn as a single entity box with a relationship line that loops back to that box or two relationship lines from the same box to a relationship symbol.
- One-to-many relationship: two different entity types connected with a 1-to-many cardinality (crow’s foot or 1..* markers).
- One-to-one relationship: two different entity types connected where each instance of one maps to at most one instance of the other (1:1).
- Associative entity (junction table): used to model many-to-many relationships as a separate entity; drawn as an entity connected to the two original entities (often with identifying relationships).

Step-by-step reasoning:
1. Inspect the diagram: the same entity symbol appears on both ends of the relationship or a relationship edge loops back to the same entity. That visual cue indicates the relationship connects the entity to itself rather than to a different entity.
2. Check cardinality markers: if the notation shows roles or cardinalities on both ends of the loop tied to the same entity type, that confirms a recursive relationship (for example, “manager” and “subordinate” roles of Employee).
3. Exclude other types: there is only one entity type involved, so it cannot be a one-to-many or one-to-one between two distinct entities. An associative entity would be a separate rectangle representing the relationship between two distinct entities, which is not shown.

Why the correct answer is correct:
- The diagram’s single entity connected back to itself is the textbook depiction of a unary (recursive) relationship. That structure explicitly models instances of the same entity relating to other instances of that same entity.

Why other options are incorrect:
- A one-to-many and a one-to-one depict relationships between two different entity types (not the same entity).
- An associative entity is a separate entity used to resolve many-to-many relationships, not a self-relationship of one entity.

Final answer: A unary relationship.

Question at position 28 In the figure below, what is depicted? A one-to-many relationshipA unary relationshipA one-to-one relationshipAn associative entity单项选择题

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