SysML FAQ: What is a Use Case diagram (UC) and how is it used?

What is a SysML Use Case diagram?

Definitions

Use Case: A Use Case (notation: oval/ellipse) represents a system transaction with an external system user, called an Actor (notation: stick-figure). Use Cases are sometimes considered high-level functional requirements.

Use Case diagram (uc): A Use Case diagram shows communications among system transactions (Use Cases) and external users (Actors) in the context of a system boundary (Subject; notation: rectangle). Actors may represent wetware (persons, organizations, facilities), software systems, or hardware systems. Defining relationships between the system Subject and the system Actors is an effective, informal way to define system scope.

Purpose

The purpose of Use Case diagrams is to provide a high-level view of the subject system and convey the top-level system requirements in non-technical terms for all stakeholders, including customers and project managers as well as architects and engineers. Additional, more rigorous SysML diagrams are needed to specify a scalable and simulatable System Architecture Model (SAM).