Multivalued dependency in DBMS

What is Multi-valued dependency?

When existence of one or more rows in a table implies one or more other rows in the same table, then the Multi-valued dependencies occur.

If a table has attributes P, Q and R, then Q and R are multi-valued facts of P.

It is represented by double arrow −

For our example:

In the above case, Multivalued Dependency exists only if Q and R are independent attributes.

A table with multivalued dependency violates the 4NF.

Example

Let us see an example &mins;

<Student>

In the above table, we can see Students Amit and Akash have interest in more than one activity.

This is multivalued dependency because CourseDiscipline of a student are independent of Activities, but are dependent on the student.

Therefore, multivalued dependency −

The above relation violates Fourth Normal Form in Normalization.

To correct it, divide the table into two separate tables and break Multivalued Dependency −

<StudentCourse>

<StudentActivities>

This breaks the multivalued dependency and now we have two functional dependencies −