Dialog Design: Principles and Experiments

Programming methodology has emphasized different criteria for judging the quality of software during the three decades of its existence. In the early days of scarce computing resources the most important aspect of a program was its functionality — what it can do, and how efficiently it works. In the second phase of structured programming the realization that programs have a long life and need continuous adaptation to changing demands led to the conclusion that functionality is not enough — a program must be understandable, so that its continued utility is not tied to its inventor. Today, in the age of interactive computer usage and the growing number of casual users, we begin to realize that functionality and good structure are also not enough — good behavior towards the user is just as important. Interactive use of computers by users with a wide variety of backgrounds, in different applications, is ever increasing.Novel styles of interfaces that exploit bitmap graphics have emerged after a long history of interactive command languages based on alphanumeric terminals. This development is repeating, with a twenty-year delay, the history of programming languages: large collections of unrelated operations are being replaced by systematic structures that satisfy general principles of consistency. We do not attempt to give a comprehensive or balanced survey of the many approaches to human-computer interface design being investigated today. We summarize a few general issues that designers of human-computer interfaces encounter, and illustrate them by means of examples from our research activities, some of them performed jointly with industry.