Database Management (Unit-4) | 4331603
Unit– IV: Refining database design through Normalization (Marks-12)
Explain Functional Dependency with suitable example. 04 – Winter-2021, 2019, 2016, 2015,
Summer-2020, 2017
What is Functional Dependency?
Let R be a relation schema having n attributes A1, A2, A3,…,An.
Let attributes X and Y are two subsets of attributes of relation R.
“If the values of the X component of a tuple uniquely (or functionally) determine the values of the
Y component, then there is a functional dependency from X to Y.”
This is denoted by X → Y (i.e RollNo → Name, SPI, BL).
It is referred as: Y is functionally dependent on the X or X functionally determines Y.
The abbreviation for functional dependency is FD or fd.
The set of attributes X is called the left hand side of the FD, and Y is called the right hand side.
The left hand side of the FD is also referred as determinant whereas the right hand side of the FD is
referred as dependent.
Functional dependency diagram and examples
Example,
o Consider the relation Account(account_no, balance, branch).
o account_no can determine balance and branch.
o So, there is a functional dependency from account_no to balance and branch.
o This can be denoted by account_no → {balance, branch}.
Explain fully functional dependency with example. 04 – Summer-2019, Winter-2015
Full Functional Dependency
In a relation, “the attribute Y is fully functional dependent on X if Y is functionally dependent on X,
but not on any proper subset of X.”
Means dependency doesn’t hold after remove of any attribute from X.
Department of Information Technology [Ms. Nikita A. Patel] 1
, Database Management (Unit-4) | 4331603
Example,
o {Roll_No, Semester, Department_Name} → SPI
o We need all three {Roll_No, Semester, Department_Name} to find SPI.
Partial Functional Dependency
In a relation, the attribute Y is partial functional dependent on X if Y is functionally dependent on
X as well as on any proper subset of X.
If there is some attribute that can be removed from A and the still dependency holds then it is partial
functional dependency.
Example,
o {Enrollment_No, Department_Name} → SPI
o Enrollment_No is sufficient to find SPI, Department_Name is not required to find SPI.
Transitive Functional Dependency
In a relation, if attribute(s) A → B and B → C, then C is transitively depends on A via B (A → C).
Example,
Staff_No → Branch_No; Branch_No → Branch_Address; then Staff_No → Branch_Address;
Explain delete anomalies. 03 – Winter-2019, 2015
What is an anomaly in database design?
Anomalies are problems that can occur in poorly planned, unnormalized database where all the data
are stored in one table.
Department of Information Technology [Ms. Nikita A. Patel] 2
Unit– IV: Refining database design through Normalization (Marks-12)
Explain Functional Dependency with suitable example. 04 – Winter-2021, 2019, 2016, 2015,
Summer-2020, 2017
What is Functional Dependency?
Let R be a relation schema having n attributes A1, A2, A3,…,An.
Let attributes X and Y are two subsets of attributes of relation R.
“If the values of the X component of a tuple uniquely (or functionally) determine the values of the
Y component, then there is a functional dependency from X to Y.”
This is denoted by X → Y (i.e RollNo → Name, SPI, BL).
It is referred as: Y is functionally dependent on the X or X functionally determines Y.
The abbreviation for functional dependency is FD or fd.
The set of attributes X is called the left hand side of the FD, and Y is called the right hand side.
The left hand side of the FD is also referred as determinant whereas the right hand side of the FD is
referred as dependent.
Functional dependency diagram and examples
Example,
o Consider the relation Account(account_no, balance, branch).
o account_no can determine balance and branch.
o So, there is a functional dependency from account_no to balance and branch.
o This can be denoted by account_no → {balance, branch}.
Explain fully functional dependency with example. 04 – Summer-2019, Winter-2015
Full Functional Dependency
In a relation, “the attribute Y is fully functional dependent on X if Y is functionally dependent on X,
but not on any proper subset of X.”
Means dependency doesn’t hold after remove of any attribute from X.
Department of Information Technology [Ms. Nikita A. Patel] 1
, Database Management (Unit-4) | 4331603
Example,
o {Roll_No, Semester, Department_Name} → SPI
o We need all three {Roll_No, Semester, Department_Name} to find SPI.
Partial Functional Dependency
In a relation, the attribute Y is partial functional dependent on X if Y is functionally dependent on
X as well as on any proper subset of X.
If there is some attribute that can be removed from A and the still dependency holds then it is partial
functional dependency.
Example,
o {Enrollment_No, Department_Name} → SPI
o Enrollment_No is sufficient to find SPI, Department_Name is not required to find SPI.
Transitive Functional Dependency
In a relation, if attribute(s) A → B and B → C, then C is transitively depends on A via B (A → C).
Example,
Staff_No → Branch_No; Branch_No → Branch_Address; then Staff_No → Branch_Address;
Explain delete anomalies. 03 – Winter-2019, 2015
What is an anomaly in database design?
Anomalies are problems that can occur in poorly planned, unnormalized database where all the data
are stored in one table.
Department of Information Technology [Ms. Nikita A. Patel] 2
