Which of the following is suitable as a description of integrity constraints in a DBMS?
a) Restrictions on the values allowed when a given item is changed are called formal restrictions.
b) Restrictions related to the data types, number of digits, and the like for a given item are called attribute restrictions.
c) Restrictions on parent-child relationships in a hierarchical database correspond to updating restrictions in a relational database.
d) Restrictions to prevent mismatches among related tables during updates are called referential constraints.