system make no sense if connectivity is lost? Is a suitable fallback available? I
should not have to worry about being unable to enter and leave my own house
because the front door lock has lost connectivity or has no power – and many
other household functions must also be taken for granted to be effective.
What is the physical context of use?
Do any parts of the system need to have particular form factors/be used in
certain contexts: e.g. worn on wrist, weatherproofed, used one handed?
How central to the service are the devices?
Are devices central to the conceptual model, or not? This may not affect the
distribution of functionality, but it will affect the way in which you
communicate the composition of the system.
9 - 20: (Summary table of composition patterns?)
Consistency
“Users should not have to wonder whether different words, situations, or
actions mean the same thing. Follow platform conventions.” Jakob Nielsen,
199412
Consistency is well known as a general UI design heuristic. It’s a simple
concept to grasp. But knowing what needs to be consistent, and what does not,
can be tricky. You may have to trade off one type of consistency for another.
Do you make all the buttons look the same so they are easy to identify as
buttons? Or does that cause confusion by implying that certain functions are
similar, when in fact they are not? Too much consistency, or consistency
between the wrong things, can be as damaging as too little.
(^12) Nielsen, J. (1994b). Heuristic evaluation. In Nielsen, J., and Mack, R.L.
(Eds.), Usability Inspection Methods, John Wiley & Sons, New York, NY.