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6.4- What Is Functional Dependency In DBMS | Functional Dependency And Normalization | Dbms Course

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Relational Database Design- Functional Dependencies And Normalization

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Functional dependencies are the result of interrelationship between attributes or in between tuples in any relation.
Definition : In relation R, X and Y are the two subsets of the set of attributes, Y is
said to be functionally dependent on X if a given value of X (all attributes in X) uniquely
determines the value of Y (all attributes in Y).
It is denoted by X → Y(Y depends upon X).
Determinant : Here X is known as determinant of functional dependency.
Consider the example of Employee relation:

In Employee relation, EID is primary key. Suppose you want to know the name and salary
of any employee. If you have EID of that employee, then you can easily find information
of that employee. So, Name and Salary attributes depend upon EID attribute.
Here, X is (EID) and Y is (Name, Salary)
X (EID) : Y (Name, Salary)
The determinant is EID
Suppose X has value 5 then Y has value (Manoj, 9,000)
6.3.1 Functional Dependency Chart/Diagram
It is the graphical representation of function dependencies among attributes in any relation.
The following four steps are followed to draw FD chart.
1. Find out the primary key attributes.
2. Make a rectangle and write all primary key attributes inside it.
3. Write all non-prime key attributes outside the rectangle.
4. Use arrows to show functional dependency among attributes.
igure 6.2.
Name
Salary
EID
Employee
FIGURE 6.2. Functional dependency chart of employee relation.
It is easier to remember all dependencies by making FD charts.
Example. Consider the following relation:
Professor (Pfcode, Dept, Head, Time) It is assumed that
(i) A professor can work in more than one dept.
(ii) The time he spends in each dept is given.
(iii) Each dept has only one head.
Draw the dependency diagram for the given relation by identifying the dependencies.

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