Functional dependency definition in DBMS Theory - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a functional dependency in a database?

A functional dependency is a relationship between two sets of attributes in a database where the value of one attribute (or set of attributes) uniquely determines the value of another attribute (or set of attributes).

beginner

Explain the notation A → B in functional dependency.

The notation A → B means that attribute A functionally determines attribute B. If two rows have the same value for A, they must have the same value for B.

intermediate

Why are functional dependencies important in database design?

Functional dependencies help identify how data is related and are used to organize tables to reduce redundancy and avoid update anomalies.

beginner

Give a real-life example of a functional dependency.

In a student database, StudentID → StudentName means the student ID uniquely determines the student's name. If two records have the same StudentID, they must have the same StudentName.

intermediate

Can a functional dependency have multiple attributes on the left side? Explain.

Yes, a functional dependency can have a set of attributes on the left side. For example, (CourseID, StudentID) → Grade means the combination of CourseID and StudentID uniquely determines the Grade.

What does the functional dependency A → B mean?

A A and B are unrelated

B B uniquely determines A

C A uniquely determines B

D A and B have the same value

A → B means if two rows have the same value for A, they must have the same value for B.

Which of the following is an example of a functional dependency?

A StudentID → StudentName

B StudentName → StudentID

C Grade → CourseID

D CourseName → StudentID

StudentID uniquely identifies StudentName, so StudentID → StudentName is a functional dependency.

Why are functional dependencies used in databases?

A To increase data duplication

B To organize data and reduce redundancy

C To make queries slower

D To delete data randomly

Functional dependencies help organize data to reduce redundancy and avoid anomalies.

Can a functional dependency have multiple attributes on the left side?

A Only in special databases

B No, only one attribute is allowed

C Only if the right side has multiple attributes

D Yes, it can have a set of attributes

Functional dependencies can have multiple attributes on the left side, like (A, B) → C.

If two rows have the same value for attribute A, what must be true for attribute B in A → B?

A They must have the same value for B

B They can have different values for B

C B must be null

D B must be unique

In A → B, same A means same B values to maintain the dependency.

Describe what a functional dependency is and why it matters in database design.

Think about how one piece of data can decide another.

Give an example of a functional dependency from everyday life and explain it.

Consider IDs and names or similar pairs.