Database Normalisation Questions Medium
Transitive dependency is a concept in database normalization that occurs when a non-key attribute is functionally dependent on another non-key attribute, rather than directly on the primary key. In other words, it is a relationship between three or more attributes in a table, where the value of one attribute determines the value of another attribute indirectly through a third attribute.
To better understand transitive dependency, let's consider an example. Suppose we have a table called "Employee" with attributes such as EmployeeID (primary key), EmployeeName, Department, and Manager. In this case, the attribute "Manager" is functionally dependent on the attribute "Department" because the manager of an employee is determined by the department they belong to. However, the manager attribute is not directly dependent on the primary key (EmployeeID), but rather indirectly through the department attribute.
Transitive dependencies can lead to data redundancy and anomalies, such as update anomalies, insertion anomalies, and deletion anomalies. To eliminate these issues and achieve a higher level of normalization, we need to decompose the table into multiple tables, ensuring that each table has only one theme or subject.
In the case of the "Employee" table, we can decompose it into two tables: "Employee" and "Department." The "Employee" table will contain attributes like EmployeeID, EmployeeName, and DepartmentID, while the "Department" table will have attributes like DepartmentID and Manager. By doing so, we remove the transitive dependency between the attributes and ensure that each table represents a single theme, thereby improving data integrity and reducing redundancy.
In summary, transitive dependency occurs when an attribute depends on another attribute indirectly through a third attribute. It is essential to identify and eliminate transitive dependencies during the normalization process to ensure a well-structured and efficient database design.