Use Cases & Scenarios

Definition

Use Cases and Scenarios describe the interactions between actors (people or systems) and the solution to achieve a specific goal. A use case defines the possible outcomes of an attempt to accomplish a goal — detailing the primary success path and the alternative or exception flows. Scenarios are concrete instances of a use case played out in a specific context. Together they are one of the most effective techniques for capturing behavioral requirements.

Inputs

• Identified actors (users, systems, or external entities) and their goals
• Business objectives and scope boundaries
• Outputs from stakeholder interviews, workshops, or observation
• Existing process models that show the workflow context

Outputs

• Use case diagrams showing actors and their associated use cases
• Detailed use case specifications with primary flow, alternative flows, and exception paths
• Scenarios illustrating specific real-world instances of use case execution
• Inputs to system design, test case development, and acceptance criteria

When to Use

• Describing how a person or system interacts with the solution to achieve a goal
• Capturing behavioral requirements for systems with multiple user types and interaction paths
• Defining scope by identifying what the system must support and what is out of scope
• As an input to test case design — each flow maps to test scenarios

When Not to Use

• Simple systems with a single user type and linear interaction — user stories may be sufficient
• Non-interactive, data-only, or purely backend solutions with no actor interactions
• When stakeholders are already aligned and a lighter-weight format is preferred