Foreign key constraints enforce referential integrity within relational database theory by establishing a mandatory logical dependency between records in distinct tables based on primary keys. This mechanism ensures that every value in the foreign attribute column exists either as a candidate key or null in the referenced table, thereby preventing orphaned data and maintaining normalization forms. As a fundamental axiom of the Entity-Relationship (ER) model implementation phase, it serves as the structural backbone for ensuring consistency across relational schemas before logical design evolves into physical storage architectures.
A foreign key is a column in a relational database table that formally references a primary key column in another table, establishing an explicit relationship between the two tables rather than a mer…