GATE CS 2024 Set 1 — Question 22

A relation is in First Normal Form (1NF) if and only if the domain of each attribute contains only atomic (indivisible) values, and the value of each attribute in a tuple contains only a single value from that domain.Analysis of Options:

• (A) $\mathbf{R}$ can have a multi-attribute key: TRUE. A candidate key or primary key can consist of multiple attributes (a composite key). This does not violate the atomicity requirement of 1NF, as long as each individual attribute in the key is atomic.
• (B) $\mathbf{R}$ cannot have a foreign key: FALSE. 1NF does not restrict the existence of foreign keys. Relations in 1NF can and often do have foreign keys to establish relationships.
• (C) $\mathbf{R}$ cannot have a composite attribute: TRUE. By definition, 1NF requires attributes to be atomic. A composite attribute (e.g., an address composed of street, city, zip) is not atomic. Therefore, a relation in 1NF cannot contain composite attributes; they must be decomposed into atomic attributes.
• (D) $\mathbf{R}$ cannot have more than one candidate key: FALSE. A relation in 1NF can have multiple candidate keys. 1NF places no restriction on the number of candidate keys.

Thus, statements (A) and (C) are true.