Sequence Diagram for the Car Rental System

Sequence diagrams illustrate the flow of messages and method calls between various actors and objects in the system as they participate in a business process. They are invaluable for visualizing how objects collaborate to complete key scenarios.

In this lesson, we will create sequence diagrams for two essential interactions in the car rental system:

• Vehicle reservation (the customer reserves a vehicle)

• Reservation cancellation (the customer cancels a reservation)

Vehicle reservation

The sequence diagram for vehicle reservation should have the following actors and objects that will interact with each other:

Actors and objects involved:

• Actor: Customer (or Receptionist, acting on behalf of a customer)

• Objects: VehicleCatalog, CarRentalSystem, VehicleReservation, Payment, Notification

Interaction steps

1. Search for vehicle:

   1. Customer requests to search available vehicles.

   2. CarRentalSystem interacts with the VehicleCatalog to retrieve available vehicles.

   3. VehicleCatalog returns a list of available vehicles.

2. Select and reserve vehicle:

   1. Customer selects a vehicle to reserve.

   2. CarRentalSystem checks if the vehicle is available.

   3. If available, the CarRentalSystem creates a new VehicleReservation object.

3. Payment processing:

   1. CarRentalSystem calculates the reservation fee.

   2. CarRentalSystem prompts the Customer for payment.

   3. Customer initiates the payment (via Payment object).

   4. Payment is processed.

      1. If successful:

         1. CarRentalSystem updates the reservation status to “confirmed.”

         2. CarRentalSystem triggers a Notification to the customer (reservation confirmation).

         3. Customer receives confirmation that the reservation is successful.

      2. If unsuccessful:

         1. CarRentalSystem deletes/cancels the reservation.

         2. CarRentalSystem triggers a Notification to the customer (reservation failed).

         3. Customer is notified that the reservation is unsuccessful.

4. Vehicle unavailability:

   1. If no vehicles are available, the CarRentalSystem notifies the Customer accordingly.

Based on the order above, the sequence diagram of a vehicle reservation in a car rental system is provided below: