Which type of dependency is eliminated by 3NF but not by 2NF?

Which type of dependency is eliminated by 3NF but not by 2NF?

• A. Transitive Dependencies
• B. Partial Dependencies
• C. Functional Dependencies
• D. Nonfunctional Dependencies

Answer: (A)

Transitive dependencies are when a non-key attribute depends on another non-key attribute that itself depends on a key attribute. In other words, you have a chain like Key → A and A → B, so the key indirectly determines B through A. Third normal form removes these chains by requiring that non-prime attributes depend only on keys, not through other non-key attributes. To fix a transitive dependency, you split the table so the attribute that determines another attribute stays in its own relation, and the attributes that depend on it move to a separate relation. For example, if a table has StudentID, DeptID, and DeptName, with StudentID → DeptID and DeptID → DeptName, then DeptName is transitively dependent on StudentID. In 3NF you’d create Student(StudentID, DeptID) and Department(DeptID, DeptName). This removes the transitive link that existed in the original table. Partial dependencies, which occur when a non-key attribute depends on part of a composite key, are handled by 2NF, not by 3NF, which is why transitive dependencies are the type eliminated by 3NF but not by 2NF.

Transitive dependencies are when a non-key attribute depends on another non-key attribute that itself depends on a key attribute. In other words, you have a chain like Key → A and A → B, so the key indirectly determines B through A. Third normal form removes these chains by requiring that non-prime attributes depend only on keys, not through other non-key attributes. To fix a transitive dependency, you split the table so the attribute that determines another attribute stays in its own relation, and the attributes that depend on it move to a separate relation. For example, if a table has StudentID, DeptID, and DeptName, with StudentID → DeptID and DeptID → DeptName, then DeptName is transitively dependent on StudentID. In 3NF you’d create Student(StudentID, DeptID) and Department(DeptID, DeptName). This removes the transitive link that existed in the original table. Partial dependencies, which occur when a non-key attribute depends on part of a composite key, are handled by 2NF, not by 3NF, which is why transitive dependencies are the type eliminated by 3NF but not by 2NF.