Database System Concepts, Avi Silberschatz, Henry F. Korth, S. Sudarshan, 2019 (McGraw-Hill Education) - A comprehensive and widely used textbook that covers the theoretical foundations of relational databases, including detailed explanations of primary keys, foreign keys, and the enforcement of referential integrity.
PostgreSQL Documentation: 5.3. Foreign Keys, The PostgreSQL Global Development Group, 2024 - Official documentation detailing the practical implementation and syntax of foreign key constraints in PostgreSQL, including various referential actions (e.g., ON DELETE, ON UPDATE) for maintaining data consistency.