Use Case Diagram for the Car Rental System

Let’s build the use case diagram for the car rental system and understand the relationship between its main actors and system functions. First, we’ll define the different elements of our system, followed by the complete use case diagram and a detailed breakdown of actors and use cases.

System

Our system is the Car Rental system. It manages automated vehicle reservations, returns, payments, and services for customers across multiple branches.

Actors

Now, we’ll define the main actors of our car rental system.

Primary actors

• Customer: The primary user, able to register, search vehicles, make and manage reservations, pick up and return vehicles, and make payments.

Secondary actors

• Receptionist: The system operator who can perform all customer operations on behalf of a customer (e.g., register a customer, search, make/update/cancel reservations, and process payments), manage vehicle inventory, and update vehicle logs.

Use cases

This section defines the use cases for the Car Rental system. We have listed the use cases according to their respective interactions with a particular actor.

Note: You’ll see some use cases occurring multiple times because they are shared among different actors in the system.

Customer

• Register account: Create a new customer profile with personal information in the system.

• Login/Logout: Securely sign in or out of the system.

• Search vehicle inventory: Search and view available vehicles by type, model, location, or availability.

• Make reservation: Reserve a vehicle for specific dates and locations, optionally selecting equipment and services.

• Update reservation: Request to add additional services such as ski rack, child seat, etc.

• Cancel reservation: Cancel an existing reservation before the scheduled pickup time.

• Pickup vehicle: Complete check-in and collect a reserved vehicle from the designated branch or location.

• Return vehicle: Complete check-out and return a rented vehicle to an authorized branch.

• Pay bill: Make payment for rental charges, including any extra services, fines, or late fees.

Receptionist

The following are a few use cases on behalf of customers:

• Register account: Create a new account for customers.

• Login/Logout: Securely sign in or out of the system.

• Search vehicle inventory: On behalf of a customer, search and view available vehicles by type, model, location, or availability.

• Make reservation: Reserve a vehicle for specific dates and locations, optionally selecting equipment and services on behalf of a customer

• Update reservation: Request to add additional services such as ski rack, child seat, etc., on behalf of a customer

• Cancel reservation: Cancel an existing reservation before the scheduled pickup time on behalf of a customer

• Add vehicle: Register a new vehicle in the branch inventory, specifying type and details.

• Remove vehicle: Remove a vehicle from the inventory (e.g., for maintenance or decommission).

• Modify vehicle info: Update vehicle information or status (e.g., availability, service state).

• Update reservation: Change details of an existing reservation, such as dates, vehicle type, or selected services.

• Update log: Record or update significant vehicle events, such as maintenance, repairs, or status changes.

• Collect bill/payment: Accept and process customer payment upon vehicle return.

Car rental system

• Send reservation notification: Automatically send reservation confirmations to customers.

• Send reservation cancellation notification: Notify customers when a reservation is canceled.

• Send overdue notification: Notify customers about overdue vehicle returns and any associated fines.

Relationships

This section describes and justifies the system’s relationships between actors and use cases. Understanding why each relationship is used will help clarify system behaviors, support extensibility, and avoid redundancy in the design.

Generalization

We’ll use the generalization relationship to add, remove, or modify a vehicle. However, each vehicle type (Car, Truck, Van, Motorcycle) may have unique attributes or business rules. By using generalization:

• The system models Add Vehicle as the common behavior.

• Each specialized use case (Add Car, Add Truck, etc.) inherits from the general use case and can include additional, type-specific steps.

• This approach improves maintainability and scalability; only a new specialized use case must be added if a new vehicle type is introduced.

• Examples:

  • Add Vehicle generalizes to Add Car, Add Truck, Add Van, and Add Motorcycle.

  • Remove Vehicle generalizes to Remove Car, Remove Truck, Remove Van, and Remove Motorcycle.

  • Modify Vehicle generalizes to Modify Car, Modify Truck, Modify Van, and Modify Motorcycle.

Associations

The table below shows the association relationship between actors and their use cases.