# Use Case Diagram

This tutorial explains to you what a UML Use Case Diagram is. Here are the concepts explanation and an example.

A use case is a methodology used in system analysis to identify, clarify, and organize system requirements.

A UML Use Case Diagram presents the main actors and their activity.

A UML Use Case diagram contains 4 components:

• The actors = usually individuals involved in that activity according to their roles. An institution (a bank, a government) could be an actor as well.
• The use cases = the specific roles played by the actors within and around the system.
• The relationships between and among the actors and the use cases.
• The boundary, which defines the system of interest in relation to the world around it (this is optional).

Here is an example of UML Use Case Diagram:

In this UML Use Case Diagram you can see: 2 actors the Client and the Waiter. What are they doing ? They are doing what the Use Cases specify:

1. The Client "Order Food", "Eat Food" and "Pay for Food".
2. The Waiter "Provide Food" when an order is received.

When you define a OrderWater Class, you must take a look of the OrderFood Class. OrderWater Class extends the OrderFood Class.

This diagram is a high level diagram and is easy to do.