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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.
Let us see an example &mins;
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 −
|StudentName ->-> CourseDiscipline|
StudentName ->-> Activities
The above relation violates Fourth Normal Form in Normalization.
To correct it, divide the table into two separate tables and break Multivalued Dependency −
This breaks the multivalued dependency and now we have two functional dependencies −
|StudentName -> CourseDiscipline|
StudentName - > Activities
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