Primary key selection: From which set is the primary key of a relation chosen in relational database design?

Introduction / Context:
Every relation should have a declared primary key. Understanding where it comes from ensures proper entity integrity and sound normalization.

Given Data / Assumptions:

• Multiple candidate keys may exist for a relation.
• Primary key is the designated identifier in the schema.
• Foreign keys create relationships to other relations.

Concept / Approach:
A candidate key is a minimal superkey—no proper subset uniquely identifies rows. The primary key is selected from the set of candidate keys to serve as the official identifier.

Step-by-Step Solution:

Verification / Alternative check:
Database design references consistently define the primary key as a chosen candidate key.

Why Other Options Are Wrong:
Composite keys: Some candidate keys are composite, but not all composites are candidate keys.
Determinants: Not necessarily minimal or unique.
Foreign keys: Reference other relations and need not be unique in the referencing table.

Common Pitfalls:
Assuming any unique set is a candidate key even if not minimal; minimality is required.

Final Answer:
candidate keys.