Interface design defies how the system will interact with external entities. System interfaces are machine made and are dealt with as a part of systems integration. User interfaces are human computer and are the focus of this chapter. Principles of user interface design include layout, content awareness, aesthetics, user experience, consistency, and user effort. The layout is the arrangement of items on the screen. Like items are grouped into areas. Areas can be further subdivided and each area is self contained. Areas should have a natural intuitive flow. Users from western nations tend to read from left to right and top to bottom. Content awareness applies to the interface in general, to each screen to each area on a screen and to sub-areas as well. Include titles on all interfaces. Menus should show where the user is and how the user got there. All areas should be well defined, logically grouped together and easily discernible visually.
Interfaces should be functional, inviting to use, and pleaseing to the eye. Simple minimalist designs are generally better. White space is important to provide seperation. Acceptable information density is proportional to the user's expertise. Color and patters matter; don't use red on blue. Ease of learning is a signifigant issue for inexperienced users. It is relevant to systems with a large user population. Ease of use is a signifigant issue for expert users. It is most important in specialized systems. Ease of learning and use of use are related. Complementary lead to similar design decisions. Consistency is extremely important concept in making the system simple. It allows the users to predict what is going to happen. All parts of the system work in the same way. Users learn how one portion works and immediately apply it to others. Key areas of consistency are navigation controls and terminology.
Interfaces should be designed to minimize the effort needed to accomplish tasks. A common rule is the three clicks rule. Users should be able to go from main menu of a system to the information they want in no more than three mouse clicks. User interface design processes examine use case and sequence diagrams. They develop use scenarios hat describing commonly employed patterns of actions. It may uncover additional requirements. Once a basic set of use scenarios have been developed, the actual user interfaces are designed. Designed interfaces are evaluated to determine if they are satisfactory and how they can be improved. Use scenarios outline the steps performed by users to accomplish some part of their work. A use scenario is one path through an essential use case. Presented in a simple narrative description. Document the most common cases so interface designs will be easy to use for those situations.
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