Question at position 32 A functional dependency between two or more non-key attributes is called a:partial nonkey dependency. partial transitive dependency. transitive dependency. partial functional dependency.

Question

BlackTom AI · Accepted Answer

A functional dependency between two or more non-key attributes is called a transitive dependency.

1. Relevant knowledge points and concepts
- Functional dependency: attribute X functionally determines attribute Y (X -> Y) if each X value maps to a single Y value.
- Key attribute: part of a candidate key that uniquely identifies tuples.
- Non-key attribute: attribute that is not part of any candidate key.
- Transitive dependency: occurs when a key determines a non-key attribute A, and A in turn determines another non-key attribute B (Key -> A and A -> B), producing an indirect dependency Key -> B through A. This violates 3rd Normal Form (3NF).
- Partial dependency: occurs when a non-key attribute depends on part of a composite primary key (violates 2NF).

2. Step-by-step reasoning
- The question specifies a dependency "between two or more non-key attributes." That means the left-hand side and right-hand side of the dependency are non-key attributes, and the relationship is not directly from the primary key.
- By definition, a transitive dependency is exactly such a scenario: Key -> X (non-key) and X -> Y (non-key), so there is a functional dependency between non-key attributes X and Y (X -> Y).
- Therefore the correct term for a dependency among non-key attributes is "transitive dependency."

3. Intermediate steps / illustrative example
- Example: EmpID (key) -> DeptID (non-key), and DeptID -> DeptName (non-key). DeptID -> DeptName is a functional dependency between non-key attributes; it is transitive because EmpID -> DeptName holds via DeptID.
- There are no numerical calculations; logical inference establishes the dependency type.

4. Why the correct answer is correct
- The defining characteristic (non-key attribute determining another non-key attribute) matches the textbook definition of transitive dependency and explains why such a dependency is problematic for 3NF.

5. Why other options are incorrect
- "Partial nonkey dependency." and "partial transitive dependency." are not standard terms; they misapply "partial" (which refers to part of a composite key).
- "Partial functional dependency." refers to a non-key attribute depending on part of a composite primary key (a 2NF violation), not to dependencies between non-key attributes.

6. Conclusion
- The correct answer is transitive dependency, which matches the provided answer.

Question at position 32 A functional dependency between two or more non-key attributes is called a:partial nonkey dependency. partial transitive dependency. transitive dependency. partial functional dependency.单项选择题

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