Task Descriptions (Use Cases)

What is a UML Use Case Diagram (UCD), and when to use it?

UML Use Case Diagrams can be used to describe the functionality of a system in a horizontal way. That is, rather than merely representing the details of individual features of your system, UCDs can be used to show all of its available functionality. It is important to note, though, that UCDs are fundamentally different from sequence diagrams or flow charts because they do not make any attempt to represent the order or number of times that the systems actions and sub-actions should be executed.

UCDs have only 4 major elements: 

1. The actors that the system you are describing interacts with, 
2. The system itself, the use cases,
3. Services, that the system knows how to perform,
4. The lines that represent relationships between these elements. 

Example Use case for travel Organizer :

1. The system displays options for investigating visa and vaccination requirements

2. The user chooses the option to find out about visa requirements.

3. The system prompts user for the name of the destination country.

4. The user enters the country’s name.

5. The system checks that the country is valid.

6. The system prompts the user for her nationality.

7. The user enters her nationality.

8. The system checks the visa requirements of the entered country for a passport holder of her nationality.

9. The system displays the visa requirements.

10. The system displays the option to print out the visa requirements.

11. The user chooses to print the requirements.

Alternative courses for travel organizer :

6. If the country name is invalid:

6.1 The system displays an error message.

6.2 The system returns to step 3.

8. If the nationality is invalid:

8.1 The system displays an error message.

8.2 The system returns to step 6.

9. If no information about visa requirements is found:

9.1 The system displays a suitable message.

9.2 The system returns to step 1.

Use case diagram for travel organizer