The success of a system is often more dependent on its ease of use than on its power. Good systems not only address the user's needs, but also provide rapid and considerate interaction. This chapter discusses human engineering, the tailoring of systems so they can be used to maximal advantage by all humans. Included in this effort is the development of a good user interface, the part of the system that communicates with the human. In addition, there must be an underlying integrity to the system so that new and unusual needs can be properly met.
This chapter discusses four areas that compose human engineering: task and user modeling, information display, command language, and feedback. Task modeling is the aspect of human engineering that runs deepest in the code since it demands a view of the task that is consistent with the user's actions and perception. This also includes a user model to predict accurately those actions and perceptions. The information display must be designed properly to prevent confusion, and is especially significant in graphics editors. Good command languages are necessary since they are the control path from the user and can create the largest bottlenecks. Finally, informative feedback keeps users happy and prevents confusion on the part of newcomers.
Human engineering must be built into systems from the start and cannot be tacked on top like some kind of macro package. Although this chapter is the last in a string of CAD system discussions, its subject matter should be considered first. The theme, however, will come as no surprise because many of the preceding chapters have echoed this cry for better thought-out systems that can be used well.
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