Referential Integrity Constraints
Referential integrity constraints are used to specify the relationships between two relations in a database.
Consider a referencing relation, R1, and a referenced relation, R2. Tuples in the referencing relation, R1, have attributed FK (called foreign key attributes) that referencethe primary key attributes of the referenced relation, R2. A tuple, t1, in R1 is said to reference a tuple, t2, in R2 if t1[FK] = t2[PK].