Design a Car Rental System

Let's design a car rental system where customers can rent vehicles.

A Car Rental System is a software built to handle the renting of automobiles for a short period of time, generally ranging from a few hours to a few weeks. A car rental system often has numerous local branches (to allow its user to return a vehicle to a different location), and primarily located near airports or busy city areas.

System Requirements

We will focus on the following set of requirements while designing our Car Rental System:

The system will support the renting of different automobiles like cars, trucks, SUVs, vans, and motorcycles.
Each vehicle should be added with a unique barcode and other details, including a parking stall number which helps to locate the vehicle.
The system should be able to retrieve information like which member took a particular vehicle or what vehicles have been rented out by a specific member.
The system should collect a late-fee for vehicles returned after the due date.
Members should be able to search the vehicle inventory and reserve any available vehicle.
The system should be able to send notifications whenever the reservation is approaching the pick-up date, as well as when the vehicle is nearing the due date or has not been returned within the due date.
The system will be able to read barcodes from vehicles.
Members should be able to cancel their reservations.
The system should maintain a vehicle log to track all events related to the vehicles.
Members can add rental insurance to their reservation.
Members can rent additional equipment, like navigation, child seat, ski rack, etc.
Members can add additional services to their reservation, such as roadside assistance, additional driver, wifi, etc.

Use case diagram

We have four main Actors in our system:

Receptionist: Mainly responsible for adding and modifying vehicles and workers. Receptionists can also reserve vehicles.
Member: All members can search the catalog, as well as reserve, pick-up, and return a vehicle.
System: Mainly responsible for sending notifications about overdue vehicles, canceled reservation, etc.
Worker: Mainly responsible for taking care of a returned vehicle and updating the vehicle log.

Here are the top use cases of the Car Rental System:

Add/Remove/Edit vehicle: To add, remove or modify a vehicle.
Search catalog: To search for vehicles by type and availability.
Register new account/Cancel membership: To add a new member or cancel an existing membership.
Reserve vehicle: To reserve a vehicle.
Check-out vehicle: To rent a vehicle.
Return a vehicle: To return a vehicle which was checked-out to a member.
Add equipment: To add an equipment to a reservation like navigation, child seat, etc.
Update car log: To add or update a car log entry, such as refueling, cleaning, damage, etc.

Use case diagram

Class diagram

Here are the main classes of our Car Rental System:

CarRentalSystem: The main part of the organization for which this software has been designed.
CarRentalLocation: The car rental system will have multiple locations, each location will have attributes like ‘Name’ to distinguish it from any other locations and ‘Address’ which defines the address of the rental location.
Vehicle: The basic building block of the system. Every vehicle will have a barcode, license plate number, passenger capacity, model, make, mileage, etc. Vehicles can be of multiple types, like car, truck, SUV, etc.
Account: Mainly, we will have two types of accounts in the system, one will be a general member and the other will be a receptionist. Another account can be of the worker taking care of the returned vehicle.
VehicleReservation: This class will be responsible for managing reservations for a vehicle.
Notification: Will take care of sending notifications to members.
VehicleLog: To keep track of all the events related to a vehicle.
RentalInsurance: Stores details about the various rental insurances that members can add to their reservation.
Equipment: Stores details about the various types of equipment that members can add to their reservation.
Service: Stores details about the various types of service that members can add to their reservation, such as additional drivers, roadside assistance, etc.
Bill: Contains different bill-items for every charge for the reservation.

Class diagram

Activity diagrams

Pick up a vehicle: Any member can perform this activity. Here are the steps to pick up a vehicle:

Return a vehicle: Any worker can perform this activity. While returning a vehicle, the system must collect a late fee from the member if the return date is after the due date. Here are the steps for returning a vehicle:

Code

Here is the high-level definition for the classes described above.

Enums, data types and constants: Here are the required enums, data types, and constants:

Python

Java

Python

class BillItemType(Enum):
  BASE_CHARGE, ADDITIONAL_SERVICE, FINE, OTHER = 1, 2, 3, 4


class VehicleLogType(Enum):
  ACCIDENT, FUELING, CLEANING_SERVICE, OIL_CHANGE, REPAIR, OTHER = 1, 2, 3, 4, 5, 6


class VanType(Enum):
  PASSENGER, CARGO = 1, 2


class CarType(Enum):
  ECONOMY, COMPACT, INTERMEDIATE, STANDARD, FULL_SIZE, PREMIUM, LUXURY = 1, 2, 3, 4, 5, 6, 7


class VehicleStatus(Enum):
  AVAILABLE, RESERVED, LOANED, LOST, BEING_SERVICED, OTHER = 1, 2, 3, 4, 5, 6


class ReservationStatus(Enum):
  ACTIVE, PENDING, CONFIRMED, COMPLETED, CANCELLED, NONE = 1, 2, 3, 4, 5, 6


class AccountStatus(Enum):
  ACTIVE, CLOSED, CANCELED, BLACKLISTED, BLOCKED = 1, 2, 3, 4, 5


class PaymentStatus(Enum):
  UNPAID, PENDING, COMPLETED, FILLED, DECLINED, CANCELLED, ABANDONED, SETTLING, SETTLED, REFUNDED = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10


class Address:
  def __init__(self, street, city, state, zip_code, country):
    self.__street_address = street
    self.__city = city
    self.__state = state
    self.__zip_code = zip_code
    self.__country = country


class Person():
  def __init__(self, name, address, email, phone):
    self.__name = name
    self.__address = address
    self.__email = email
    self.__phone = phone

Account, Member, Receptionist, and Additional Driver: These classes represent different people that interact with our system:

Python

Java

Python

# For simplicity, we are not defining getter and setter functions. The reader can
# assume that all class attributes are private and accessed through their respective
# public getter methods and modified only through their public methods function.

from abc import ABC, abstractmethod

class Account(ABC):
  def __init__(self, id, password, person, status=AccountStatus.NONE):
    self.__id = id
    self.__password = password
    self.__status = AccountStatus.NONE
    self.__person = person

  def reset_password(self):
    None


class Member(Account):
  def __init__(self):
    self.__total_vehicles_reserved = 0

  def get_reservations(self):
    None


class Receptionist(Account):
  def __init__(self, date_joined):
    self.__date_joined = date_joined

  def search_member(self, name):
    None


class AdditionalDriver:
  def __init__(self, id, person):
    self.__driver_id = id
    self.__person = person

CarRentalSystem and CarRentalLocation: These classes represent the top level classes:

Python

Java

Python

class CarRentalLocation:
  def __init__(self, name, address):
    self.__name = name
    self.__location = address

  def get_location(self):
    return self.__location


class CarRentalSystem:
  def __init__(self, name):
    self.__name = name
    self.__locations = []

  def add_new_location(self, location):
    None

Vehicle, VehicleLog, and VehicleReservation: To encapsulate a vehicle, log, and reservation. The VehicleReservation class will be responsible for processing the reservation and return of a vehicle:

Python

Java

Python

from abc import ABC, abstractmethod

class Vehicle(ABC):
  def __init__(self, license_num, stock_num, capacity, barcode, has_sunroof, status, model, make, manufacturing_year, mileage):
    self.__license_number = license_num
    self.__stock_number = stock_num
    self.__passenger_capacity = capacity
    self.__barcode = barcode
    self.__has_sunroof = has_sunroof
    self.__status = status
    self.__model = model
    self.__make = make
    self.__manufacturing_year = manufacturing_year
    self.__mileage = mileage
    self.__log = []

  def reserve_vehicle(self):
    None

  def return_vehicle(self):
    None


class Car(Vehicle):
  def __init__(self, license_num, stock_num, capacity, barcode, has_sunroof, status, model, make, manufacturing_year, mileage, type):
    super().__init__(license_num, stock_num, capacity, barcode,
                     has_sunroof, status, model, make, manufacturing_year, mileage)
    self.__type = type


class Van(Vehicle):
  def __init__(self, license_num, stock_num, capacity, barcode, has_sunroof, status, model, make, manufacturing_year, mileage, type):
    super().__init__(license_num, stock_num, capacity, barcode,
                     has_sunroof, status, model, make, manufacturing_year, mileage)
    self.__type = type


class Truck(Vehicle):
  def __init__(self, license_num, stock_num, capacity, barcode, has_sunroof, status, model, make, manufacturing_year, mileage, type):
    super().__init__(license_num, stock_num, capacity, barcode,
                     has_sunroof, status, model, make, manufacturing_year, mileage)
    self.__type = type


# We can have similar definition for other vehicle types

# ...

class VehicleLog:
  def __init__(self, id, type, description, creation_date):
    self.__id = id
    self.__type = type
    self.__description = description
    self.__creation_date = creation_date

  def update(self):
    None

  def search_by_log_type(self, type):
    None


class VehicleReservation:
  def __init__(self, reservation_number):
    self.__reservation_number = reservation_number
    self.__creation_date = datetime.date.today()
    self.__status = ReservationStatus.ACTIVE
    self.__due_date = datetime.date.today()
    self.__return_date = datetime.date.today()
    self.__pickup_location_name = ""
    self.__return_location_name = ""

    self.__customer_id = 0
    self.__vehicle = None
    self.__bill = None
    self.__additional_drivers = []
    self.__notifications = []
    self.__insurances = []
    self.__equipments = []
    self.__services = []

  def fetch_reservation_details(self, reservation_number):
    None

  def get_additional_drivers(self):
    return self.__additional_drivers

VehicleInventory and Search: VehicleInventory will implement an interface ‘Search’ to facilitate the searching of vehicles:

Python

Java

Python

from abc import ABC, abstractmethod

class Search(ABC):
  def search_by_type(self, type):
    None

  def search_by_model(self, model):
    None


class VehicleInventory(Search):
  def __init__(self):
    self.__vehicle_types = {}
    self.__vehicle_models = {}

  def search_by_type(self, query):
    # return all vehicles of the given type.
    return self.__vehicle_types.get(query)

  def search_by_model(self, query):
    # return all vehicles of the given model.
    return self.__vehicle_models.get(query)

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