Derived Attributes & Methods in Object-Oriented Databases

1. Introduction

In object-oriented databases, attributes and methods can be classified into various types. This lesson focuses on derived attributes and derived methods, which are essential for effective data management and retrieval.

2. Definitions

• Derived Attribute: An attribute whose value is calculated or derived from other attributes rather than being stored directly.
• Derived Method: A method that computes a value or performs an action based on the current state of an object, often derived from other methods or attributes.

3. Derived Attributes

Derived attributes help reduce redundancy and improve data integrity. Instead of storing the same data in multiple places, derived attributes calculate their values on demand.

Example of a Derived Attribute

class Order {
    private double totalPrice;
    private List items;

    public double getTotalPrice() {
        return items.stream().mapToDouble(Item::getPrice).sum();
    }
}

In this case, the totalPrice is derived from the prices of the individual items in the order.

4. Derived Methods

Derived methods perform calculations or return values based on the object's state. These methods can simplify complex operations and enhance code readability.

Example of a Derived Method

class Employee {
    private double baseSalary;
    private double bonus;

    public double calculateTotalCompensation() {
        return baseSalary + bonus;
    }
}

The calculateTotalCompensation method derives the total compensation from the base salary and bonus attributes.

5. Best Practices

• Always document derived attributes and methods to clarify their purpose.
• Use derived attributes for frequently accessed data to reduce computation time.
• Ensure that derived methods are efficient and do not perform heavy calculations unnecessarily.
• Keep derived attributes and methods consistent with their original data sources to prevent discrepancies.

6. FAQ