Question at position 49 Relational databases establish the relationships between entities by means of common fields included in a file called a(n):entity.relation.association.relationship.单项选择题
A
entity.
B
relation.
C
association.
D
relationship.

Question

Question at position 49 Relational databases establish the relationships between entities by means of common fields included in a file called a(n):entity.relation.association.relationship.

BlackTom AI · Accepted Answer

A relation (commonly called a table) in a relational database contains rows and columns and is the structure used to link entities via common fields.

1. Relevant knowledge points and concepts
- Relational model: Data are organized into relations (tables). Each relation has attributes (columns) and tuples (rows).
- Primary key: A column (or set) that uniquely identifies tuples in a relation.
- Foreign key: A column in one relation that refers to the primary key of another relation, creating a link between entities.
- Terminology distinctions: entity refers to a real-world object or instance; association/relationship are informal terms for how entities are connected, while relation is the specific file/table structure in the relational model.

2. Step-by-step reasoning
- The question asks for the name of the file (structure) that includes common fields used to establish relationships.
- In the relational model relationships are implemented by storing common fields (keys) in tables.
- The formal term for such a file/structure is "relation" (the theoretical term) or "table" in practical DBMSs.

3. Intermediate logical steps
- Entities are represented as tuples/rows within a relation.
- To link two entities, a foreign key column in one relation contains values matching the primary key in another relation.
- Thus the common fields reside in a relation.

4. Why the correct answer is correct
- "Relation." precisely names the database object where columns (common fields) and key constraints are defined; it is the canonical term in relational database theory.

5. Why other options are incorrect
- "Entity.": An entity is a real-world thing, not the file/table containing fields.
- "Association.": Informal; not the formal name of the file/structure in relational theory.
- "Relationship.": Describes the concept of how entities are linked, but not the file that contains the common fields.

6. Conclusion
Therefore the correct choice is relation., which matches the provided answer. Final answer: relation.

Question at position 49 Relational databases establish the relationships between entities by means of common fields included in a file called a(n):entity.relation.association.relationship.单项选择题

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Question at position 32 Relational databases establish the relationships between entities by means of common fields included in a file called a(n):association.relationship.entity.relation.

Question at position 29 Unlike columns, the rows of a relation may not be interchanged and must be stored in one sequence. TrueFalse

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