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Scenarios of use (Use cases)

Summary

Scenarios specify how users carry out their tasks in a specified context. They provide examples of usage as an input to design, and provide a basis for subsequent usability testing. They are user- and task-oriented use cases.

Benefits

  • It encourages designers to consider the characteristics of the intended users, their tasks and their environment.
  • Usability issues can be explored at a very early stage in the design process (before a commitment to code has been made).
  • Scenarios can help identify usability targets and likely task completion times.
  • The method promotes developer buy-in and encourages a user-centred design approach.
  • Scenarios can also be used to generate contexts for evaluation studies.
  • Only minimal resources are required to generate scenarios.
  • The technique can be used by developers with little or no human factors expertise.

Method

An experienced moderator is recommended for the sessions in which the scenario is explored.

  • Gather together the development team and other relevant stakeholders under the direction of an experienced facilitator.
  • Identify intended users, their tasks and the general context. This information will provide the basis for the scenarios to be created by the development team.
  • Functionally decompose user goals into the operations needed to achieve them.
  • Consider which activities should be performed by the user and which by the computer.
  • Create an outline of the users' activities, goals and motivations for using the system being designed, and the tasks they will perform.
  • To maintain design flexibility, scenarios should not specify what product features are used.
  • Assign task time estimates and completion criteria as usability targets.
  • The session can be videotaped for later review or transcribed for wider distribution.
  • The results from scenario building sessions can be used to plan user-based evaluations.

Practical guidelines

Try to generate scenarios to cover a wide range of situations, not just the most common ones or those of most interest to the design team.

Try to include problem situations that will test the system concept, not just straightforward scenarios.

Work through the scenarios fully and judge the system on that basis rather than trying to change the system half way through.

More information

Scenarios are most useful when produced early in development as specific realistic and detailed examples of what a user would do, but without making any reference what user interface features that would be used. See the examples.

Scenarios can also be used later to explore how the interface would be operated.

Next steps

Use the scenarios as a basis for developing more specific usability requirements.

Case studies

Background reading

The following books and web sites provide more information:


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