Does a proper relation allow cells that hold multi-valued entries (e.g., lists or arrays inside a single cell)?

Introduction / Context:
First Normal Form (1NF) requires atomicity: each cell in a relation must contain a single, indivisible value from its attribute domain. The question asks whether multi-valued cells are permitted in a relation.

Given Data / Assumptions:

• We are talking about the relational model, not semi-structured stores.
• Atomicity applies uniformly across all attributes.
• Examples of multi-valued entries include comma-separated lists, arrays, or nested tables stored in one cell.

Concept / Approach:
Multi-valued cells violate 1NF. In a properly normalized design, each value occupies its own row in a related table connected by keys. This ensures simpler constraints, predictable querying, and avoids update anomalies (insertion, deletion, and modification anomalies).

Step-by-Step Solution:

Verification / Alternative check:
Normalize by splitting multi-valued data into a child relation (e.g., ProductColor(product_id, color)). Each color then resides in its own tuple, satisfying atomicity.

Why Other Options Are Wrong:

• “Correct” contradicts 1NF.
• Restrictions to non-key attributes or warehouse contexts do not change the relational definition; they are practical compromises, not theoretical allowances.

Common Pitfalls:
Storing CSV strings, arrays, or JSON blobs for convenience leads to difficult querying and constraint enforcement.

Final Answer:
Incorrect