Class Diagram for the Online Stock Brokerage System

In this lesson, we'll identify and design the classes, abstract classes, and interfaces based on the requirements that we have previously gathered from the interviewer in an online stock brokerage system.

Components of a stock brokerage system#

As mentioned earlier, we will design the online stock brokerage system using a bottom-up approach.

Account#

Account is an abstract class that is used to store the account information of a person. This class has members like account ID, password, account status, address, email, and phone number. There can be two types of accounts, i.e., Admin and Member.

Member: They can search the stock, place an order to buy or sell stocks, create an account, start a membership, add stocks to the wishlist, add buying and selling limits, as well as perform transactions in many ways.

Admin: They can block or unblock members, and cancel their membership.

Watchlist#

A list of stocks that an investor keeps an eye on to profit from price drops is called a watchlist. The visual representation of the Watchlist class is provided below.

Stock#

A stock is also known as equity. It is a security that represents a portion of the issuing company's ownership. The Stock class will have a symbol, price, etc.

Search and stock inventory#

The StockInventory class will retrieve and keep up with the most recent stock values from the StockExchange class (defined later). The StockInventory class implements the Search interface.

Stock position#

All the stocks that the user owns will be included in the StockPosition class.

Stock lot#

A member may purchase various lots of the same stock at various dates. The StockLot class will represent these particular lots.

Order#

Members can place stock trading orders when they want to sell or acquire stock positions. There are four types of orders supported by the system:

MarketOrder: This allows customers to purchase or sell equities immediately at the market's going rate (current market price).

LimitOrder: A user may specify a price at which they wish to purchase or sell a stock.

StopLossOrder: An order to purchase or sell whenever the stock hits a specific price.

StopLimitOrder: The StopLimitOrder becomes a limit order to purchase or sell at the limit price, or better, if the stop price is reached.

Order part#

Multiple order parts might be used to complete an order. The OrderPart class contains the price, quantity, and execution date.

Deposit and withdraw money#

The DepositMoney class represents a transfer of money from one party to another.

The WithdrawMoney class represents removing money from an account.

Transfer money#

Users should be able to deposit and withdraw money either via check, wire, or electronic bank transfer.

Notification#

Notification is an abstract class. This class is responsible for sending notifications when trade orders are executed. Every notification has an ID, creation date, and content in it. The notification can either be an SMS notification or an email notification.

The SmsNotification class requires the phone number of the member to send a notification. The EmailNotification class needs the email address of the member to send a notification. The relationship diagram of these classes is shown here:

Stock exchange#

The stock brokerage system will get all stocks from the stock exchange and their current pricing. The StockExchange class is responsible for creating orders for trading stocks on the stock exchange.

Enumerations and custom data types#

The following provides an overview of the enumerations and custom data types used in this problem:

• OrderStatus: We need to create an enumeration to keep track of the status of the order, whether it is open, filled, partially filled, or canceled.

• TimeEnforcementType: We need to create an enumeration for the time enforcement type, whether it is good till canceled, fill or kill, immediate or cancel, on the open, or on the close.

• AccountStatus: We need to create an enumeration to keep track of the status of the account, whether it is active, canceled, closed, blacklisted, or none.

Address#

We also need to create a custom data type, Address, that will store the location of the user.

Relationship between the classes#

Now, we'll discuss the relationships between the classes we have defined above in our online stock brokerage system.

Association#

The class diagram has the following association relationships:

One-way association#

• The StockInventory class has a one-way association with Watchlist and StockExchange.

• The Order class has a one-way association with Stock, StockExchange, and StockLot.

• The Account class has a one-way association with Order, DepositMoney, and WithdrawMoney.

• The StockPosition class has a one-way association with the Order class.

Two-way association#

• The Notification class has a two-way association with the Order class.

• Both Watchlist and StockPosition have a two-way association with the Account class.

Composition#

The class diagram has the following composition relationships:

• The Order class is composed of OrderPart.

• The StockInventory class is composed of Stock.

• The StockPosition class is composed of StockLot.

Inheritance#

The following classes show an inheritance relationship:

• Both Admin and Member extend the Account class.

• The MarketOrder, LimitOrder, StopLimitOrder, and StopLossOrder classes extend the Order class.

• The ElectronicBank, Wire, and Check classes extend the TransferMoney class.

• The SmsNotification and EmailNotification classes extend the Notification class.

• The StockInventory class implements the Search interface.

Note: We have already discussed the inheritance relationship between classes in the component section above one by one.

Class diagram of the online stock brokerage system#

Here is the complete class diagram for our online stock brokerage system:

Design pattern#

In the online stock brokerage system, there is going to be only one instance of the stock exchange, which encloses all the information and relations relating to the stock exchange. Therefore, we use the Singleton design pattern to ensure that only one instance for the class is created and this instance has a global point of access.

We can also use the Observer design pattern for our online stock brokerage system. Since the user has set buying and selling limits, the system observes stock prices, and when a stock reaches the specified price it buys and sells the stock automatically. Therefore, there is a need for an observer who observes the price of stock all the time.

AI-powered trainer#

At this stage, everything should be clear. If you encounter any confusion or ambiguity, feel free to utilize the interactive AI-enabled widget below to seek clarification. This tool is designed to assist you in strengthening your understanding of the concepts.

We have successfully designed the class diagram for the online stock brokerage system. Let's move to the next lesson to see how we can construct the sequence diagram for the system.