Overall structuring of user interfaces in iterative software development processes

Systems emerge incrementally in iterative software development processes. While functionality add-ons can be tackled more easily by current software development techniques, incremental expansions of a system are difficult to handle from a usability point of view. Usage related details are defined and revised over longer periods of time alongside the incremental development of a system. Only fragmented and incomplete information is available at the beginning of the development process. However, even when substantial parts of detailed information are missing it might be possible to envisage the whole picture at a higher level of abstraction with more or less blurred parts of the composition if adequate means to represent that picture are available. Proper notations that allow designers to capture an initial sketchy view as well as to fit in details over time can make the whole of the picture bigger than the sum of its part and thus be a very useful guidance resource. A consistent initial picture even with many details still missing mitigates substantially usability problems that might be caused by incremental functionality add-ons. Instead of using flat abstract structural models of user interfaces, the use of hierarchical models allow the addition of more details at lower levels over time while at higher levels a consistent and a more stable representation of the system as virtual space to carry out work can be sketched out at very early stages of an iterative development process.