The design process builds on a strong conceptual model. Iterative review and refinement includes user feedback at all critical stages. Design is based on user activity and employs the user's language and context. The design model fits the user's mental model rather than the technical implementation model.
Interaction design is treated as distinct from technical design.
While these techniques have helped large software development projects meet time, budget and usability goals, they do not directly address usability issues. Because most systems being developed today are interactive, software development methodology must be expanded to include the design of the user interface. Many people contributed to its development including Whitney Quesenbery, Scott Gilkeson and Janis Morariu.