Editing Use case (section)

== Visual modeling ==
{{UML diagram types}}

Use cases are not only texts but also diagrams if needed. In the [[Unified Modeling Language]], the relationships between use cases and actors are represented in [[use case diagram]]s originally based upon [[Ivar Jacobson]]'s [[Objectory]] notation. [[SysML]] uses the same notation at a system block level.

In addition, other behavioral UML diagrams such as [[activity diagram]]s, [[sequence diagram]]s, [[communication diagram]]s, and [[UML state machine|state machine diagrams]] can also be used to visualize use cases accordingly. Specifically, a [[System Sequence Diagram]] (SSD) is a sequence diagram often used to show the interactions between the external actors and the system under design (SuD), usually for visualizing a particular scenario of a use case.

Use case analysis usually starts by drawing use case diagrams. For agile development, a requirement model of many UML diagrams depicting use cases plus some textual descriptions, notes, or ''use case briefs'' would be very lightweight and just enough for small or easy project use. As good complements to use case texts, the visual diagram representations of use cases are also effective facilitating tools for the better understanding, communication, and design of complex system behavioral requirements.