501 Introduction to Functional Dependency PDF

! 501 Introduction to Functional Dependency In relational databases, functional dependency is a concept that defines a relationship ** ** betwe...

! 501 Introduction to Functional Dependency In relational databases, functional dependency is a concept that defines a relationship ** ** between two sets of attributes in a table. It is an essential concept in database normalization, helping to ensure data consistency and reduce redundancy. ** Functional dependencies form the basis for defining normal forms, which help organize data ** efficiently within a database. Definition of Functional Dependency * * A functional dependency, denoted as X → Y , exists between two sets of attributes X and ** ** ` ` ` ` ` Y if, for every unique value of X , there is a corresponding unique value of Y. ` ==* ` ` * * ** ** ` ` *== This doesn't mean that Y must be unique across the entire table. *** ** * ` ` ~~ ~~ ==* It simply means that for any specific value of X , * * * ` ` == == the corresponding Y is the same every time X appears. ` ` * ** ** ` ` ** *** == * This means that the value of Y is determined by the value of X. ` ` ** ** ` ` * ==* In other words, X uniquely determines Y. * ` ` *** * ** ` ` == ** ` X is called the determinant. ` ** ** == == ** ** ` Y is called the dependent. ` ** ** == == ** * Example of Functional Dependency * ** ** Consider the following Student table, which contains information about students , their ` ` ` ` ` roll numbers , names , and departments. ` ` ` ` ` * In this table: * ** ` Roll Number → Name : ` ** The Roll Number uniquely determines the Name of each student. ` ` * * ` ` * For example, if we know the Roll Number is 101 , we can determine that the Name is ** *** ` ` ` ` ` ` * "Alice Smith." * This indicates a functional dependency from Roll Number to Name. ** ** ` ` ` ` ** ` Roll Number → Department : ` ** * Similarly, Roll Number also uniquely determines the Department for each student , * ` ` * * ` ` ` ` so there is a functional dependency from Roll Number to Department. ** ** ` ` ` ` Appendix: ==* Think of it as "If I know the Roll Number then I can always find the student's name ". ` ` ` ` *== Importance of Functional Dependency in Database * * Design ** Functional dependencies are essential for ensuring data integrity and organizing data ** * efficiently. * They help identify the relationships between attributes and are used to define database * * * * ** normal forms, which are guidelines for structuring tables to reduce redundancy and avoid ** anomalies. ** Data Consistency: Functional dependencies ensure that each value of an attribute is * *** * unique and consistent when determined by another attribute. * * * ** Normalization: They are fundamental in the process of database normalization, which ** reduces data redundancy and helps maintain database integrity. ~~ ~~ * * ** Elimination of Anomalies: By identifying and organizing functional dependencies, we ~~ ~~** can reduce insertion, update, and deletion anomalies. * * ~~ ~~ (See Appendix: Anomalies) [[ ]]