Use Case diagram for captureing "Customer Voice"

Initial stage of software project, Business modeling and Requirement analysis play a major role. Use Case diagram mainly used for capture the requirements. Use case diagram building blocks are

Actor
A role that interacts with the system.
Represents a role, not individuals; can be a person or a device or another system.
Communicate with the system by sending and/or receiving messages.
An actor may participate in many use cases; a use case may have several actors participating in it. 


Use Case

• Is an abstraction of a set of sequences that yield some functionality.
• Represents some user-visible function.
• Is always initiated by an "actor" 
• Describes the interaction between the actors and the system for a system function.
• Achieves a discrete goal for the actor.

Use Case Diagram
A graphical representation of the Use Cases of a system, its actors, and the interaction between them.