What does referential integrity ensure in a relational database?

Referential integrity is a critical concept in relational databases, and it specifically pertains to the relationships between tables. Through referential integrity, a database ensures that relationships between tables remain consistent. This means that for every foreign key in a table that references a primary key in another table, the foreign key must match an existing primary key value, or it must be null.

This mechanism helps to maintain the accuracy and reliability of data across related tables. By enforcing that foreign keys correspond to valid primary keys, the database prevents orphaned records and ensures that data referencing is valid. For instance, if a foreign key in a child table does not correlate with a primary key in a parent table, it would indicate that there is a broken link in the relationship, potentially leading to misleading or inconsistent data.

The other options relate to important concepts in database design but do not specifically define what referential integrity is about. While uniqueness of primary keys is a requirement for primary keys themselves, and proper field definitions and normalization are important for overall database structure and performance, they do not directly address the relationship aspect that referential integrity governs. Therefore, the essence of referential integrity lies in ensuring that each foreign key corresponds to an existing primary key, thus maintaining data integrity within the relational model