Information Technology Reference
itself [6,7]. Evidently, invisibility is not to be referred to physical dimensions of
a component but rather to its seamless integration with the surrounding
environment. Weiser in  states that a good instrument is an invisible one,
citing as example the eyeglasses. While wearing them, a person does not focus
on them as a primary object but rather on seeing better. This is definitely not
the case with a personal computer, which still forces the user's attention on the
instrument itself rather than on the task to be accomplished, so often captured
by stalls and failures.
Dimensions are thus irrelevant, and Weiser states that invisible systems
may be built at all scales, inch-, foot- and yard-scale  as long as users are
not distracted by the devices in which they are immersed .
2.1 User-centric versus desktop-centric systems
Let us consider a current desktop system: it is intrinsically devoted to a single
user who may perform a single or multiple concurrent tasks. For instance,
user may be writing an email or reading a web page, while listening to a
music track and scanning the hard drive for viruses and trojans. In all cases,
the running computer programs are in control of the interaction, leaving
the user to choose within a predefined set of possibilities; the interface may
change its aspect, at times presenting a command line while a windows
environment in others, but the users must always be knowledgeable of the
interface syntax at all times and renounce to their freedom of choice in how
to accomplish the task. As this interaction occurs mostly at machine level ,
users are subjected to the following three unfortunate consequences: (i) must
be familiar with the computing device and well-trained on using its interface;
(ii) must create their own mental map to associate labels and icons to specific
tasks and devices and (iii) perceive the interface as unnatural and get easily
distracted from the task.
To this desktop-centric vision, the ubiquitous systems community
opposes a user-centric one, in which the user is at the centre of the
environment and computing systems are embedded all around to support the
needs and desires. In other words, users move freely in their selected
environment, be their house, the office or a public space and the objects in
the environment sense their presence and act according to the users' requests.
The point of view is now reversed, as the flow of interaction is now
controlled by the individual and not by the computer, Computers become
context-aware , as it is conscious of its capabilities and owns information
about the environment where it operates. These computer devices can both
relate to each other and to the users, dynamically adapting to the needs of the
user controlling them . Interaction, therefore, moves from an explicit
level to an implicit one.