AMU 2026 — Computer PYQ

Why is 3 NF considered adequate?

In practical relational database design, Third Normal Form (3 NF) is widely targeted and accepted as the industry standard for a clean design. It balances efficiency, minimizes data redundancy, and eliminates update anomalies while ensuring that the database remains functionally complete without unnecessary overhead.

A relation is in 3 NF if it is in 2 NF and no non-prime attribute is transitively dependent on the primary key:

$$\text{If }X\to Y\text{ holds, then either }X\text{ is a super key or }Y\text{ is a prime attribute.}$$

Why BCNF is often not the standard default:

While Boyce-Codd Normal Form (BCNF) is a stronger variant of 3 NF, achieving BCNF can sometimes force a schema decomposition that loses dependency preservation. Because preserving functional dependencies is critical for performance and integrity checks during insertions, database architects usually settle for 3 NF as the optimal choice.

Analysis of other options:

• (a) 2 NF: It eliminates partial dependencies, but allows transitive dependencies, which still leaves the table highly vulnerable to insertion, deletion, and update anomalies. Thus, it is inadequate.

• (c) 4 NF: It addresses multi-valued dependencies. While mathematically superior, it is rarely required or implemented in everyday business applications unless specialized multi-valued constraints exist.