Use case modelling is a structured technique for capturing how different types of users interact with a system to achieve specific goals. Originating in software engineering and associated with the Unified Modelling Language (UML), use cases have been adopted by UX practitioners as a systematic way to document the scope of interactions a product must support. A well-written set of use cases prevents both scope creep and scope blindness by making every intended user interaction explicit before design begins.
What It Is
A use case describes a single goal-oriented interaction between a user (called an 'actor') and a system. It specifies the actor, the goal, the main success scenario (the step-by-step happy path), and the alternative paths that occur when something goes differently. Use case diagrams provide a visual overview of all the use cases and actors in a system. Together they create a complete inventory of what a product needs to do from the user's perspective.
How to Run It
- Identify all the user types (actors) who will interact with the system.
- For each actor, list the goals they need to accomplish using the product.
- Write a use case for each actor-goal pair: name the use case, describe the main success scenario step by step, then document alternative flows.
- Create a use case diagram showing all actors and their associated use cases.
- Review use cases with stakeholders to verify completeness and accuracy.
- Prioritise use cases for design and development based on user frequency and business value.
When to Use It
Use case modelling is most valuable during requirements definition on complex products with multiple user types and many distinct interaction scenarios. It is particularly effective for enterprise software, government services, healthcare platforms, and any product where the scope of required functionality is large and diverse. Use it to create a shared baseline between design, development, and product management before any design work begins.
Tips for Success
- Write use cases at the right level of abstraction — one goal per use case, not one screen interaction.
- Document the alternative flows with the same rigour as the main success scenario: edge cases are where UX fails.
- Link use cases to personas so that the human motivation behind each interaction remains visible.
- Treat use cases as living documents: update them as design decisions reveal new constraints or opportunities.
