1. Use Case Diagrams
Examples

2. Example 1

3. A vending machine sells small, packaged, ready to eat items
A vending machine sells small, packaged, ready to eat items. Each item has a price and a name. A customer can buy an item, using cash or coins to pay for it. The customer presses a letter and then a number from a keypad located under item they wish to purchase. The vending machine will push the chosen item forward, allowing the item to drop in the tray at the bottom of the machine. The vending machine will subtract the amount of money the item was worth from the amount inserted into the machine and will return this amount through a change slot. The customer puts their hand through the swinging cover of the vending machine tray and takes item.
The maintenance employee is responsible for recharging the machine with items when the machine gets low on stock. He also monitors the machine by checking number of items sold, number of items sold per type and total revenue. The administrator sets up the machine by defining items sold and prices for each item.

4. Example 2

5. Railway Reservation System is a system used for booking tickets over Internet. Any customer can book tickets for different trains. Customer can book a ticket only if the tickets are available. Customer searches for the availability of tickets then if the tickets are available he books the tickets by initially filling details in a form and the tickets will be issued. The customer then will be able to print the issued ticket. The customer can cancel the booking and refund his money. Draw a use case diagram.