Explain in detail the following question regarding referential integrity in Database Systems: a. The concept of referential integrity and why it is extremely important in a relational system. b. Assuming that referential integrity is enforced by the DB engine. What happens if you try to delete a tuple in table A whose attribute id is a foreign key in table B? c. Assuming that referential integrity is enforced by the DB engine. What happens if you try to insert a tuple in table B whose foreign key id does not exist in table B?