Let for any relation R, IR represents operation insert into R and DR represents operation delete from R. Assume that a relation R2 has a foreign key that refers to primary key of another relation R1. Two operations that may cause violation of referential integrity constraints are:

Question

Accepted Answer

The correct option is (4):
The two fundamental operations that can violate the principle of **Referential Integrity** are inserting a record into the child table or deleting a record from the parent table. The operation **IR2 (Insert into R2)** can cause a violation if the value supplied for the foreign key in the new R2 record does not match any existing value in the primary key of the parent table R1. This would create an 'orphaned' child record pointing to a non-existent parent, which is a direct violation of the FK constraint. Similarly, the operation **DR1 (Delete from R1)** can violate the constraint if the primary key record being deleted is currently referenced by one or more existing foreign key records in the child table R2. Unless the foreign key constraint is explicitly defined with a **CASCADE** rule, the database management system must either reject the deletion or enforce a **RESTRICT** action to prevent the creation of orphaned records, which is noted as a violation. Thus, both scenarios are primary causes of integrity constraint breaches.

The incorrect option is (1):
The pair **IR1 (Insert into R1)** and **IR2 (Insert into R2)** is incorrect because inserting a new record into the parent table (R1) with a new primary key value can never, by itself, violate referential integrity. The purpose of a primary key is simply to ensure uniqueness and non-null values within R1, and adding a new, unique key simply creates a new valid target for foreign keys in R2 to potentially reference in the future. While the second operation, IR2, certainly *can* cause a violation if its foreign key value is invalid, the combination as a whole is not the most accurate representation of the two distinct problematic scenarios. The most significant integrity failures occur when references are broken or invalid ones are created.

The incorrect option is (2):
The pair **DR1 (Delete from R1)** and **DR2 (Delete from R2)** is incorrect because deleting a record from the child table (**DR2**) cannot cause a referential integrity violation. Referential integrity rules ensure that every foreign key value in the child table (R2) has a matching primary key in the parent table (R1). When a record is removed from the child table, its foreign key reference is also removed. This action naturally removes a link, which makes the database schema *more* compliant with integrity rules, as it eliminates a foreign key entirely, rather than leaving a dangling reference.

The incorrect option is (3):
The pair **IR1 (Insert into R1)** and **DR2 (Delete from R2)** is incorrect because neither of these two operations independently causes a violation of referential integrity constraints. As explained, **IR1 (Insert into R1)** simply adds a new valid primary key to the parent table, which is a key concept in database design and does not break any existing links. Similarly, **DR2 (Delete from R2)** removes an entire child record, which includes the foreign key value, thereby eliminating the reference without creating any data inconsistency or orphans. Since neither operation can result in a state where a foreign key points to a non-existent primary key, this combination is invalid.