Information Technology Reference
2.4 Explicit HCI
Explicit interaction takes place by means of visual interfaces where information
is coded through 'icons'. In this respect, the designer has the goal to build an
interface enabled with visual consistency that allows the user to make sense of
it. Widgets, icons, windows, menus and all the components of a GUI represent
the moves of a dialogue between the user and the system. They have to be
designed following some 'usability principles' (refer to  for a detailed
explanation of this topic). In a GUI, the 'point-and-click' metaphor replaces the
command line interface where the user has to learn a suitable language to issue
commands by digitizing them on a keyboard.
Modern usable interfaces have to obey three main principles:
The general principles can be articulated in several facets that define in
detail the requirements of a usable interface.
Generalizability is a crucial usability principle that can be regarded as a
particular facet of learnability. Generalizability refers to the interface's
capability to allow simple interaction in a new application context based on
the knowledge of similar situations in other applications. Generalizability is
strictly related to consistency, that is, the ability of the interface to exhibit a
similar behaviour to other applications when the user has to face similar
tasks. Consistency can be referred to whatever feature is in the interface, and
it is often measured in terms of the I/O behaviour.
Another important usability principle when designing an interface is its
recoverability , that is, a particular facet of robustness. Recoverability is the
ability of the users to recover from the errors when they detect them.
Recoverability allows the users to exert control over the task they are
carrying on through interface because they are able to come back from an
erroneous interaction path and they are always prompted about possible
errors related to the next move.
Finally, the designer has to take care of those interface's components that
carry a particular meaning; such elements have to be designed in order to
draw the attention towards them. One can use a particular arrangement of
shape, colour and position to achieve this goal.
The concept of usability has been standardized by ISO, even if usability
principles have not been coded as design rules, and they are the result of
several best practices in the design process . A designer has to follow them
to obtain a good interface that allows the user to have a good dialogue with