User model and system model: the yin and yang in user-centered software development

Software systems can be viewed from both external and internal perspectives. They are called user model and system model respectively in the human-computer interaction community. In this paper, we employ the yin-yang principle as an analytical tool for reviewing the relationship between the user model and the system model. In the traditional system-centered approach, the engineer is more concerned with the system model and does not pay much attention to the user model. However, as the user-centered approach has gained increasing acceptance in a number of projects, we claim that the user model and system model are the yin and yang in user-centered software development and, following the yin-yang principle, call for equal emphasis on both models. Particularly, we propose using video-based scenarios as the representation of user models and reveal the benefits of the use of video in software development. As a case study, we describe how we have employed scenario videos in a project course and share best practices that we have identified for the creation of demo scenario videos.