Multivalued dependencies (MVDs): are they harmless? "Multivalued dependencies create harmless anomalies that can be noted but need not be eliminated."

Introduction / Context: Multivalued dependencies (MVDs) arise when two or more sets of attributes vary independently with respect to a key. If left in the same relation, MVDs introduce redundant combinations and classic anomalies. This question challenges the notion that MVDs are harmless and can be ignored.

Given Data / Assumptions:

• MVD example: STUDENT has independent sets {SKILL} and {HOBBY}; storing both lists together inflates rows.
• Fourth Normal Form (4NF) is intended to remove redundancy from MVDs by decomposition.
• We are focused on logical integrity, not performance shortcuts.

Concept / Approach: When MVDs are present, each independent set combines with the other, producing a Cartesian-like explosion of rows. This inflates storage and creates update anomalies: changing one list requires touching many rows; deleting an entry may remove unrelated facts. 4NF decomposes the table into separate relations keyed by the same determinant, eliminating the artificial combinations and restoring integrity.

Step-by-Step Solution:

Verification / Alternative check: Compare row counts pre- and post-decomposition. The inflated product of independent lists disappears in 4NF, while information content remains identical via joins.

Why Other Options Are Wrong:

• Calling MVDs harmless ignores real update/insert/delete anomalies.
• FKs and indexes do not eliminate redundancy caused by MVDs.
• Dimensional models may tolerate controlled denormalization, but that is a deliberate trade-off, not evidence that MVDs are harmless in OLTP schemas.

Common Pitfalls: Storing comma-separated lists; believing that validation at the application tier makes MVD redundancy acceptable; overlooking effects on analytics and reporting accuracy.

Final Answer: Invalid (MVDs cause redundancy and anomalies; 4NF addresses them)