Task: Define Use-Case Scenarios
This task describes how to define the main use-case scenarios.
Disciplines: System Engineering Requirements
Purpose
To capture a set of essential scenarios for each use case. These will be later on merged into a common workflow (described by an activity diagram).
Relationships
RolesPrimary Performer: Additional Performers:
InputsMandatory:
    Optional:
    • None
    Outputs
      Main Description

      Use case scenarios represent the interactions of the system executing the use case with the actors. Each scenario represents a specific sequence of events, messages, and actions. Each of these elements captures at least part of a requirement, and often more than one requirement, specifying a required or optional sequence, input and output events and messages, and control and data transformations.

      A use case normally has between several and several dozen such scenarios and each scenario has typically several to several dozen messages. The scenarios set is said to be 'minimally complete' when each functional or quality of service requirement is represented on at least one scenario. Messages between the use case and the actor(s) are normally represented as asynchronous events that optionally carry data. This constitutes the so-called 'logical interface' between the actors and the system as it executes the use case.