A foreign key may be null and still adhere to the referential integrity constraint.

The entity integrity rule states that:

A. no primary key attribute may be null.

B. no primary key can be composite.

C. no primary key may be unique.

D. no primary key may be equal to a value in a foreign key.

When mapping a many-to-many unary relationship into a relation which of the following is true?

A. One relation is created.

B. Two relations are created.

C. Three relations are created.

D. Four relations are created.

If no multivalued attributes exist and no partial dependencies exist in a relation, then the relation is in what normal form?

A. First normal form

B. Second normal form

C. Third normal form

D. Fourth normal form

A foreign key is which of the following?

A. Any attribute

B. The same thing as a primary key

C. An attribute that serves as the primary key of another relation

D. An attribute that serves no purpose