Activity-centered design (ACD), which is an approach to interaction design, does not focus on the goals and preferences of the user, but on how users behave when performing particular tasks. Activities can be defined as actions and decisions that are done for a purpose. They can be easy and fast, or hard and time consuming. Examples range from making a sandwich to learning a language. The activity stops when the person performing it, or an outside force, ends it. A cello is a product that was designed using activity-centered design.
The purpose of an activity is not always a goal, it can be something more tangible. An example of an activity could be raking leaves. In that case a tidy yard would be a goal, but the purpose of raking would be collecting leaves.
The tasks, which activities are made up of, also have a purpose. That is to engage in an activity. Thus, a task is a moment in the life of an activity, and many of those moments can be aided by design. Pushing a button is an example of a task. If pushing that button is as a part of several steps that leads to the launch of for instance a nuclear missile, pushing the button would be a part of an activity that leads to the movement of the missile.
When working with activity-centered design, the designers use research to get insights of the users. Observations and interviews are typical approaches to learn more about the users behavior. By mapping users' activities and tasks the designer may notice missing tasks for the activity to become more easy to perform, and thus design solutions to accomplish those tasks.
