Software Engineering for Students A Programming Approach

54 Chapter 5 ■ User interface design
It is common in user interface design to distinguish between principles and guidelines
(or rules):
■ principles are high level and general. An example of a principle is: maintain consistency
throughout the interface.
■ guidelines are specific and detailed. An example of a guideline is: black text on a
white background is clearer than white text on a black background.
Guidelines are direct, immediate and therefore easy to apply, but principles have to be
interpreted and applied to the specific system.
5.2 ● An inter-disciplinary field
User interface design or human–computer interaction (HCI) is very much an interdisciplinary
subject, with contributions from computer science, cognitive psychology,
sociology and ergonomics. Cognitive scientists are concerned with how human beings
perceive the world, think and behave at an individual level. Sociologists study groups of
people and their interactions. Ergonomics is about designing systems that are easy to
use. Software engineers must often take responsibility for user interface design as well
as the design of the software to implement that interface. These different disciplines
bring different perspectives to bear on designing the human–computer interface.
User interface design has as much to do with the study of people as it does with technology.
Who is the user? How does the user learn to interact with a new system? How
does the user interpret information produced by the system? What will the user expect
of the system? These are just a few of the questions that must be answered as part of
user interface design. User interface design must take into account the needs, experience
and capabilities of the user. It is nowadays considered important that potential
users should be involved in the design process.
The different specialisms reflect different views about the interaction between people
and computers. At one level it is possible to view HCI as the interaction between one
individual and the computer. At this level, the concerns are about such things as the
amount of information displayed on the screen and the colors chosen. In the workplace,
however, the computer system is often part of the wider context of the work being carried
out. Usually, other people are also involved in the work, so that the sociology of
the workplace has a role. The questions here may be: Who does what? How can person
A and person B communicate most effectively?
5.3 ● Styles of human–computer interface
The manner in which users tell the computer what they want to do has changed dramatically
over the last ten years. Broadly, there have been three types of interface: command
line, menu and GUI (graphical user interface).
In the early days of computing, the only mode of HCI was the command line interface.
Communication was purely textual and was driven either via commands or by