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The user should always know where he is and how he can navigate in order to reach the desired information. This can be achieved by using overviews, table of contents, index, navigational diagrams, fish eye view, etc. The user should be able to return to previous stages in the dialogue using an Undo facility. The ease with which the user can navigate through a system is vital to its overall level of usability. One of the most common design faults with a multimedia system is to present a screen containing graphical objects which is visually attractive, but where and it is not clear what are control, input or output areas, and what is simply the background. By creating a common style and screen areas for interaction controls and input and output areas, the user quickly learns where to look to interact with the system. It is also important to allow the user to reverse actions in a simple way and to easily exit from the system at any time. With World-Wide-Web browsers, the most commonly used button is the "Back" key. This is presented in a prominent place (top, left), and is available at all times. This is especially necessary in relation to speech recognition. The possibility of an multilevel undo which allows the user to go back step by step and take the end point as a new starting point is desirable. Another problem is not knowing which path to select to navigate forward through the system. High level menu options may not be specific enough to describe all the options at lower levels, and there will always be items that are hard to classify. Allowing the user to step back, having followed an incorrect path through the system, is one way to overcome this problem. Another is to provided a 'look-ahead' facility whereby the user can click on a menu option and see in advance the next level of menu before an item is selected. The use of 'walkthrough menus' is also helpful whereby the user can explore a menu structure before making a choice. Of course careful design of menu option captions is the simplest and most effective way of assisting users to select options.
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Copyright EMMUS 1999.
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