The norm "Ergonomic requirements for office work with visual display terminals (VDTs) - Part 11: Guidance on usability ()" by the International Standards Organisation (ISO) defines usability as ["the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use"].
Well, what does it mean in our context? An application or service for mobile users may be usable if these people are familiar with the use of mobile devices fulfilling well known tasks after a short training course. However, if we change the context or preconditions it might be not well usable. This could be the case, if people are unfamiliar with mobile computing or communication devices, or if they shall fulfill other tasks without training.
In other words, software cannot be usable in all contexts for all people for all kinds of tasks. Therefore, it is very important in a usability engineering process throughout the life of your project to define and verify all these circumstances and preconditions and to harmonise it with the requirements of your contractor.
Copyright © 2001-2003 by Rainer Hillebrand and Thomas Wierlemann