Table of Contents
Functional Dependency in DBMS
Functional Dependency in DBMS is the basic of Database Normalization. In this tutorial we will learn about Functional Dependency Concepts such as functional dependency introduction, functional dependency example .and Inference rules for functional dependency with example.
Frequently Asked Questions
Some frequently asked questions asked from functional dependency are are given below –
What is functional dependency in DBMS ?
What are different inference rules for functional dependencies ?
What is Functional Dependency in DBMS ?
- Functional Dependency is a relationship between two attributes.
- Functional dependency represents the relationship between the primary key and non-primary key attributes.
- An arrow denotes a functional dependency.
- If there are two attributes X and Y of a relation R then functional Dependency of attribute X on attribute Y can be represented as an X -> Y.
- Functional dependency also plays an important role to make the database design better.
- Functional Dependency is the types of constraints that are based on key concepts.
Functional Dependency Example
In this section, we will understand the functional dependency example. Consider the example given below
| Employee ID | EmployeeName | Salary | City |
| E1 | Rohit | 12000 | Bijnore |
| E2 | Amit | 20000 | Moradabad |
In the above Relation, we can determine the employee name, city and salary by the employee id. So we can say that EmployeeName , Salary and City attributes are functionally dependent on EmployeeID.
So for the above table we can the functional dependency in following form
- EmployeeID -> EmployeeName
- EmployeeID->Salary
- EmployeeID ->city
Terms for Functional Dependency in DBMS
Dependent – Dependent attribute is denoted at the right side of the arrow in a functional dependency.
Axiom – Axioms is the collection of inference rules used to infers all functional dependencies on a database.
Determinant – In functional dependency notation, the determinant is written at the left side of the arrow.
Inference Rules for Functional Dependency
Inference rules are the rules related to functional Dependency in DBMS.
Inference rules are applied to the given functional Dependency and generate some new functional dependency. Inference rules are some assertion.
There are following inference rules in DBMS are related to functional Dependency.
Reflexive Rule
If Y is a subset of X, then we can say that X determines Y, and this is denoted as
X->Y, If X ⊇ Y
Augmentation Rule
The augmentation rule is also called partial Dependency.
If X-> Y, then according to this rule, we can write XZ->YZ.
Transitive Rule
According to the transitive rule, if X->y and Y->Z, we can write X->Z.
Union Rules
As per the union rule, if X->y and X->z, then we can say that
X->YZ
Decomposition Rule
This rule is just the reverse of the Union Rule. According to this rule, we can write.
if X->YZ then X->Y, X->Z
Conclusion and Summary
In this functional dependency in DBMS tutorial we have explained the basic concepts of functional dependency and inference rules.
After reading this tutorial students will be able to answer the questions based on functional dependency.
