Question

Which of the following situation may require the use of null values?

• A. When a particular attribute does apply to an entity.
• B. Value of an attribute is unknown, although it exists.
• C. Known because it does exist.
• D. None of the above.

Answer 1

The correct option is B Value of an attribute is unknown, although it exists.

Absence of a data item is represented by a special value called null value. Following are the situation which require the use of null values:
1. When a particular attribute does not apply to an entity;
2. Value of an attribute is unknown, although it exists;
3. Unknown because it does not exist.