In early computer systems, the technology was relatively more expensive than the personnel who used the system. As a result, engineering considerations dominated designs and users were forced to adapt to the system. As technology has become relatively inexpensive and more powerful, there has been an increasing emphasis on fitting the system to the user. Although the emphasis is shifting, human - computer interaction is essentially a situation of mutual adaptation or accommodation ([ 30]Norman and Draper, 1986).
To accommodate the user, the designer must employ (either explicitly or implicitly) some theory or model of user behavior. Much of the research in human - computer interaction is aimed at building such a theory or theories ([ 27]Card, Moran, and Newell, 1983). System design involves constructing a conceptual model of how the system is to function. In adapting to the system, the user also develops a conceptual model of the system as a guide to his or her interaction and dialogue with the system.
Inconsistencies between the designer's model of the system and the user's model of the system create potential for error. Such inconsistencies arise because the primary means for communicating the designer's model to the user is through the physical system (and its accompanying documentation). Thus, inconsistencies can arise when the system fails to accurately reflect the designer's model (i.e., the system has bugs), or when the user's experience with the system results in a misinterpretation of the model embodied in the system. From this perspective a good system not only has few bugs but also has a conceptual model that is clearly evident in the technological artifact itself. The use of metaphors, such as the desktop metaphor popularized by Apple Macintosh, is a useful means of conveying a conceptual model of the system to users ([ 28]Gerlach and Kuo, 1991).
In addition to having a conceptual or mental model of the system, the user also has a model of the...