The technological explosion of the 1970s has resulted in the development of very complex systems. The user interface also known as the Man-Machine Interface (MMI) became a general concern to both systems designers and researchers. The term user interface has been defined "as those aspects of the system that the user come in contact with" (Moran, 1981, p.4). The term "user friendly" was later coined to refer to a system that a user can easily interact with through its interfaces. In the mid- 1980s the developing field of user interface design began to include aspects such as organizational issues, work practices, design, implementation and evaluation amongst others. A broader term "human-computer interaction" (HCI) was then adopted to describe this new field. Today, HCI is taught as a course (or as part of a course) in the computer science and information systems curricula of most universities. The knowledge in the field of human- computer interface development is intertwined, with no clear beginning or end. Designers of user interfaces must draw from as many sources of information as can be obtained at reasonable cost. User interface designers try to satisfy the human requirements of a system by applying knowledge from many areas: cognitive psychology, input and output devices, guidelines and standards, dialogue types, and (because design knowledge is inadequate) prototyping methods. It is multidisciplinary (Preece et al., 1994).