Abstract
When the usability practice is extended to the development of large-scale software, usual usability expertise is not sufficient to evaluate the characteristics of large-scale software development. By introducing the viewpoint of temporal sequence of operations of software products and systems, however, we can extend the usual usability concept and define five classes of usability practices. This extended concept can be defined as the natural usability, which is comprised of five classes of usability practices. In this paper, the characteristics of each class of natural usability are also briefly examined and explained.
