Defining use cases
A use case is an artifact that defines a sequence of actions that yields an observable result of value. Use cases provide a structure to express functional requirements within the context of business and system processes. Use cases can be represented as a graphical element in a diagram and as a use case specification in a textual document.
A business use case defines a sequence of actions that a business performs that yields an observable result of value (a work output) to a particular business actor or that shows how the business responds to a business event.
A system use case is a sequence of actions that a system performs that yields an observable result of value to a particular actor (someone or something outside the system that interacts with the system).
A use case diagram can include multiple use cases and the relationships between use cases and the persons, groups, or systems that interact to perform the use case.
You can create an actor artifact that provides textual detail for an actor in a use case diagram. An actor artifact can be used in multiple use case diagrams.
Use case specifications share the same rich-text behavior that is present in all artifacts based on the text artifact format. The specifications often include content that is based on a template or process guidance. For a sample use case specification outline, see Use case specification outline.