In today’s computing environment the user interface is a key factor in determining a program’s success or failure. The reasons for this are easy to understand. First, the look and feel of a program defines the initial user experience. Thus, it forms the user’s first impression—and first impressions matter because they often become lasting impressions. Second, the user interface is the way in which a user interacts with a program each time it is used. Therefore, the overall quality of a program is judged, in part, by the usability and appeal of its interface. To be successful, a user interface must be convenient, ...