Use case Diagrams:

In order to define a system, it is important to define the behavior of the system when it is running/operator or in other words, the dynamic nature of the system. There are five types of UML diagrams available of which use case diagram is one. It needs both internal or external factors for making the interaction.

Use cases are system functionalities written in an organized manner. The diagram consiste of a few components.

1. Internal or external agents known as actors
2. Functionalities represented as use cases
3. Relationships among use cases and actors

A use case diagram is normally used in cases where system events and flows are to be clearly specified. There are other diagrams that allow users to understand data flow, etc. This is a high level diagram that provides details on each cases's functionality, its inputs and outputs.

Use cases are normally drawn based on BA's understanding and then further refined through discussions and collaborations. When written down or with the help of notes, use cases can also provide information on exceptions, pre-conditions and post conditions. Such detailed use cases can be used as an input for testing.

Some important actions to be taken when drawing a use case diagram are as mentioned below:

1. Name of the use case should determine and clearly explain its functionality.
2. The actors should be suitably named depending on their role in real world.
3. Dependencies and relationships should be explicitly denoted and easy to understand.
4. The use case point should clarify all sorts of requirements. Do not try to explain all relationships in the same diagram and this would just reduce readability.

Below is an example of a use case diagram