Design rationale is about the reasons for design decisions.
Is often represented using annotated images.
•Is useful for collating design issues across different areas of expertise (e.g. mechanical engineering and human factors).
•Colour, font etc. can be modified to give an at-a-glance overview.
The image below shows a simple example of a design rationale image.
Potential problems have been indicated using normal font with a red arrow; advantageous features have been shown using italic with a green arrow.
Other methods that fit well with design rationale:
•Upward laddering on goals and values, to find out the reasons for a design preference.
•Downward laddering on explanations, to unpack technical terms and avoid misunderstandings.
•Observation to find out how people actually use something.
•Idea generation techniques such as constraint relaxation, to find solutions to design problems.