User-Centred Requirements Handbook |
Scenarios are characterisations of users and their tasks in a specified context. They offer concrete representations of a user working with a computer system in order to achieve a particular goal. The primary objective of scenario building is in the early phases of a development cycle to generate end user requirements and usability aims. The scenarios are created by the members of a development team who then role play what it is like to be a user, in order to form a group-wide user model based on consensus. Scenarios may also be discussed with users to establish how they would like or not like to interact with the system (in general terms).
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.
Limitations
Scenarios are not appropriate for considering the details of interface design and layout.
What you need
The resources required are minimal and scenarios should be quick to produce (perhaps just a few hours?). An experienced moderator is recommended for the sessions in which the scenario is explored, and up to 2 hours per session may be required.
Process
The principle steps for this method are as follows:
1. Gather together the development team and other relevant stakeholders under the direction of an experienced facilitator.
2. 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.
3. Functionally decompose user goals into the operations needed to achieve them.
4. Assign task time estimates and completion criteria as usability targets.
5. The session can be video-taped for later review or transcribed for wider distribution.
6. The results from scenario building sessions can be used to plan user-based evaluations.
In terms of output, the method encourages a deeper understanding of user requirements and can be specifically used to plan subsequent 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.
Further information
Clark (1991), Nielsen (1991).