Which database concept enforces rules on data entry?

• A. Bubble Sort
• B. Concurrency
• C. Connection Pool
• D. Constraint

Answer: (D)

Rules on data entry in a database are enforced by constraints. A constraint defines what values are allowed and how data relates to other data, helping maintain data integrity across the system. Examples include NOT NULL (a value is required), UNIQUE (no duplicates), CHECK (limits on allowed values), and FOREIGN KEY (referential integrity with related tables). Because every insert or update must satisfy these rules, constraints are the mechanism that enforces data-entry rules. The other concepts don’t serve this purpose: bubble sort is a sorting algorithm, concurrency deals with multiple processes accessing data at once, and a connection pool manages reusable database connections.