Database software performs three main types of integrity services: semantic,referential, and entity. Which of the following correctly describes one of these services?

i.A semantic integrity mechanism makes sure structural and semantic rules are enforced.
ii. A database has referential integrity if all foreign keys reference existing primary keys.
iii. Entity integrity guarantees that the tuples are uniquely identified by primary key values.

A.
i,ii, iii

B.
ii, iii

C.
i, ii

D.
i

Explanation:
A semantic integrity mechanism makes sure structural and semantic rules are enforced. These rules pertain to data types, logical values, uniqueness constraints, and operations that could adversely affect the structure of the database. A database has referential integrity if all foreign keys reference existing primary keys. There should be a mechanism in place that ensures no foreign key contains a reference to a primary key of a nonexisting record, or a null value.Entity integrity guarantees that the tuples are uniquely identified by primary key values. For the sake of entity integrity, every tuple must contain one primary key.If it does not have a primary key, it cannot be referenced by the database.