Multivalued Dependency in DBMS: Definition and Examples

A multivalued dependency in a database occurs when one attribute in a table determines multiple independent values of another attribute, regardless of other attributes. It means that for a single value of one column, there can be multiple values of another column, independent of the rest of the table.

How It Works

Imagine you have a table where one column controls two other columns independently. For example, a student can have multiple phone numbers and multiple hobbies. The phone numbers and hobbies are independent of each other but both depend on the student.

This situation is called a multivalued dependency. It means that knowing the student lets you find all their phone numbers and all their hobbies separately, but phone numbers and hobbies do not affect each other.

In database terms, if attribute A multivaluedly determines attribute B, then for each value of A, there is a set of values of B that appear independently of other attributes.

Example

This example shows a table with students, their phone numbers, and hobbies. The student determines multiple phone numbers and multiple hobbies independently.

plaintext

Student | PhoneNumber | Hobby
--------|-------------|-------
Alice   | 123-4567    | Chess
Alice   | 123-4567    | Painting
Alice   | 987-6543    | Chess
Alice   | 987-6543    | Painting
Bob     | 555-1234    | Soccer
Bob     | 555-1234    | Reading

Output

Shows that for Alice, phone numbers and hobbies combine independently, causing repeated rows.

When to Use

Understanding multivalued dependencies helps in designing databases to avoid redundancy and update anomalies. When a table has multivalued dependencies, it is a sign to split the table into smaller tables to keep data clean.

For example, if you store students with multiple phone numbers and hobbies in one table, you get repeated rows. Instead, create one table for student-phone numbers and another for student-hobbies.

This improves data integrity and makes the database easier to maintain.

Key Points

• Multivalued dependency means one attribute determines multiple independent sets of another attribute.
• It causes data repetition if not handled properly.
• Normalization to Fourth Normal Form (4NF) removes multivalued dependencies.
• Helps keep databases efficient and consistent.

Key Takeaways

Multivalued dependency occurs when one attribute determines multiple independent values of another.

It causes repeated data if stored in a single table without separation.

Splitting tables to remove multivalued dependencies improves database design.

Fourth Normal Form (4NF) addresses multivalued dependencies.

Recognizing multivalued dependencies helps maintain data integrity and reduce redundancy.