Let's now imagine that we have a restaurant system in which a customer can order food. The chef prepares the food and the manager keeps track of the sales, as shown in the following diagram:

From the preceding diagram, we can see that we have three actors (the Customer, the Chef, and the Manager). We also have different use cases—Check Menu, Order Food, Cook Food, Serve Food, Pay, and Sales Report, which are connected to one or more actors. The Customer actor is involved in the Check Menu, Order Food, and Pay use cases. The Chef has to access Order Food in order to find out about the orders. The Chef is also involved in the Cook Food and Serve Food use cases. Unlike the Chef and the Customer, the Manager is able to see the Sales Report of the restaurant.

By looking at this use case diagram, we are able to identify the functionalities of the system. It doesn't give you any implementation details, but we can easily see an overview of the system.