Derived Attribute in DBMS

A derived attribute is an attribute whose value is calculated or derived from other attributes in the database, rather than being stored directly.

  • Essentially, the data for a derived attribute is not stored in the database but is computed dynamically from the values of one or more other attributes.



Examples of Derived Attributes in DBMS

Let explain some important examples of derived attributes in DBMS

i. Age from Date of Birth

  • Base Attribute: Date_of_Birth
  • Derived Attribute: Age
  • Explanation: Instead of storing Age directly, which changes every year, we calculate it dynamically using the current date.
  • Formula: Age = Current Date – Date_of_Birth
  • Use Case: Useful in student or employee databases to always have up-to-date age without manual updates.

ii. Total Salary from Basic Salary and Bonus

  • Base Attributes: Basic_Salary, Bonus
  • Derived Attribute: Total_Salary
  • Explanation: Storing Total_Salary would require recalculation whenever Basic_Salary or Bonus changes. Instead, it can be derived dynamically.
  • Formula: Total_Salary = Basic_Salary + Bonus
  • Use Case: Payroll systems, financial reports.

iii. Years of Experience from Join Date

  • Base Attribute: Join_Date
  • Derived Attribute: Experience
  • Explanation: Automatically calculate how long an employee has been with the company without manually updating each year.
  • Formula: Experience = Current Date – Join_Date
  • Use Case: Employee performance evaluation, promotions, or benefits eligibility

Representation of Derived Attributes in DBMS

In Entity-Relationship (ER) diagrams, derived attributes are often represented with a dashed oval. Here is a graphical representation of derived attributes in a DBMS. Consider a table Employee with 4 attributes and 3 derived attributes are given below

Derived Attribute in DBMS - Graphical Representation

Why Use Derived Attributes?

  • Efficient Storage: Storing the value of a derived attribute may result in redundancy. By deriving the value from other attributes, you save space and avoid repeating the same information.
  • Improved Performance: In cases where the value of an attribute is frequently calculated but not always required, it’s more efficient to calculate it on demand rather than store it permanently.
  • Real-time Data: Derived attributes ensure that the values are always up-to-date since they are calculated in real-time whenever needed, based on the current state of the data.

Benefits of Derived Attributes

  1. Space Efficiency: Since derived attributes are calculated rather than stored, they reduce the amount of storage needed in the database.

  2. Data Integrity: Derived attributes always reflect the most up-to-date values, ensuring that calculations are based on the latest data.

  3. Flexibility: It allows for more dynamic and flexible queries, as the system can always calculate derived values based on the current data, rather than retrieving pre-calculated (and possibly outdated) values.

  4. Reduced Redundancy: Since derived attributes avoid duplication, they help maintain a more normalized database, reducing redundancy and the potential for inconsistent data.

Handling Derived Attributes in DBMS



When designing a database, it’s important to handle derived attributes carefully. Here are a few considerations:

  • Avoid Storing Redundant Data: In some cases, it might be tempting to store the value of a derived attribute. However, it’s usually better to avoid this unless there are performance reasons for storing the value.

  • Use Proper Calculation Logic: Ensure that the formula or logic used to derive the value is correctly defined and implemented within the database or application code.

  • Consider Performance: Calculating derived attributes, especially complex ones, might be resource-intensive. In such cases, you might choose to store the calculated value in a temporary table or use database triggers to update it periodically.

Derived vs. Non-Derived Attributes

  • Non-Derived Attributes: These attributes store actual data and don’t rely on any other attribute for their value. Examples include Name, Address, and Employee_ID.

  • Derived Attributes: As explained, derived attributes depend on other attributes for their values, such as Age, Total Salary, and Years of Experience.

Conclusion

Derived attributes are an essential concept in DBMS, allowing for efficient data storage, accurate real-time calculations, and improved data integrity. By calculating values dynamically instead of storing them, databases become more optimized and avoid unnecessary redundancy.