There are four principles for
usability:
-
Provide a
good conceptual model.
The design model is the designer’s conceptual
model. The user’s model is the mental model developed through interaction with
the system. The system image results from the physical structure that had been
built. The designer expects the user’s model to be identical to the design
model. But the designer doesn’t talk directly with the user – all communication
takes place through the system image. If the system image does not make the
design model clear and consistent, then the user will end up with the wrong
mental model.
-
Make
things visible.
It is important that in the design the
possibilities are visible. When for instance, controls have multiple functions,
but not all functions are clear, the system is not understandable; its
capabilities aren’t apparent. In fact, the relationships among the user’s
intentions, the required actions, and the results are completely
arbitrary.
-
The
principle of mapping
Mapping is a technical term meaning the
relationship between two things, in this case between the controls and their
movement and the results in the world. Consider the mapping relationships
involved in steering a car. To turn a car to the right, one turns the steering
wheel clockwise. The user must identify two mappings here: one of the controls
on the dashboard controls affects the steering, and the steering wheel must be
turned in one of two directions. Both are somewhat arbitrary. But the wheel and the clockwise
directions are natural choices: visible, closely related to the desired outcome,
and providing immediate feedback. The mapping is easily learned and always
remembered.
-
The
principle of feedback
Feedback – sending back to the user information
about what actions has actually been done, what result has been accomplished –
is a well-known concept in the science of control and information theory.
Imagine trying to talk to someone when you cannot even hear your own voice:
there would be no feedback.