Use Case diagrams

Use Case diagrams

• How the systems behaves from a user’s standpoint
• Captures what the system is for the user
• What all things can the user do, meaning what are all the functionality ?
• Essential part of requirements analysis
• Use case is a high piece of functionality
• Emphasizes on what/who rather than how
• Used to communicate with clients
• Directly mapped to test cases
• Not advised to proceed further without completing use cases

Use Case

Summary of scenarios for a single task or goal

Scenario

• A sequence of steps describing an interaction between user & system
• Includes all-goes-well case and things-going-wrong cases

Actor

• Anybody (human) or anything (external system) interacting with the system
• Initiates the events involved in that task

Preconditions

• Any conditions that have to be met before the use case can start
• A precondition may be another use case
• Not mandatory

Flow of Events

• Primary flow
• Auxiliary flow

Post conditions

• Conditions that must be true after the primary flow is complete
• Not mandatory

Relationships

• Generalizations
• Use case
• Actor
• Includes
• Extensions

Example

Exercise

• A project management system that provides following functionalities :
• A project manager may add, delete & update projects.
• For deleting, it is necessary to find the project to be deleted.
• When updating projects :  
• A project manager may manage tasks by selecting the task option. 
• A project manager may manage resources by selecting the resource option. 
• The project manager can publish a project schedule by sending e-mail to project team members or by generating a web-site on a web-site host. 
• The system will be used by part-time and full-time project managers.