Functional dependency is a relationship that exists when one attribute uniquely determines another attribute. Here X is a determinant set and Y is a dependent attribute. Each value of X is associated with precisely one Y value. Functional dependency in a database serves as a constraint between two sets of attributes.

Functional Dependency (FD) is a constraint that determines the relation of one attribute to another attribute in a Database Management System (DBMS). Functional Dependency helps to maintain the quality of data in the database. It plays a vital role to find the difference between good and bad database design.

A functional dependency (FD) is a relationship between two attributes, typically between the PK and other non-key attributes within a table. For any relation R, attribute Y is functionally dependent on attribute X (usually the PK), if for every valid instance of X, that value of X uniquely determines the value of Y.

2. DEFINATION • Functional dependency is a relationship that exists when one attribute uniquely determines another attribute. If R is a relation with attributes X and Y, a functional dependency between the attributes is represented as X->Y, which specifies Y is functionally dependent on X.

Functional dependency in DBMS, as the name suggests is a relationship between attributes of a table dependent on each other. Introduced by E. F. Codd, it helps in preventing data redundancy and gets to know about bad designs.

A functional dependency is a constraint that specifies the relationship between two sets of attributes where one set can accurately determine the value of other sets. The attribute set on the left side of the arrow, X is called Determinant, while on the right side, Y is called the Dependent.

Main characteristics of functional dependencies used in normalization:

• have a 1:1 relationship between attribute(s) on left and right-hand side of a dependency;
• hold for all time;
• are nontrivial.

The functional dependency is a relationship that exists between two attributes. It typically exists between the primary key and non-key attribute within a table. The left side of FD is known as a determinant, the right side of the production is known as a dependent.

1. A “functional dependency” A->B simply means that no two different values of B are ever related to the same A.
2. Since a key must be unique, even if two tuples contain the same value of some attribute(s), the key values must be different nonetheless.

To understand the concept thoroughly, let us consider P is a relation with attributes A and B. Functional Dependency is represented by -> (arrow sign) Then the following will represent the functional dependency between attributes with an arrow sign −

Definition: A functional dependency (FD) on a relation schema R is a constraint X → Y, where X and Y are subsets of attributes of R. Definition: an FD is a relationship between an attribute “Y” and a determinant (1 or more other attributes) “X” such that for a given value of a determinant the value of the attribute is uniquely defined. i.

• The attributes of a table is said to be dependent on each other when an attribute of a table uniquely identifies another attribute of the same table. 3. • For example: • Suppose we have a student table with attributes: Stu_Id, Stu_Name, Stu_Age.

Transitive dependency A functional dependency is said to be transitive if it is indirectly formed by two functional dependencies. X -> Z is a transitive dependency if the following three functional dependencies hold true: X->Y Y does not ->X Y->Z A transitive dependency can only occur in a relation of three of more attributes.