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spoken language are redundant, i.e. nodding one's head and saying 'yes'. Such
implicit knowledge is used to make the information more clear.
Applications can be improved by implicit HCI. The application I/O and
its execution environment have to be analysed to this aim; in turn, the context
of use has to be evaluated along with the application feedbacks.
2.3 What is 'context'?
The word 'context' has a lot of meanings in computer science, according to
the particular research field like natural language processing, image under-
standing, computer architectures and so on [2].
A complete definition of 'context' in HCI can arise by focusing on the
following five questions:
Who . Current computer systems focus the interaction on a particular user
regardless of the other ones in the same environment. As human beings,
we adapt our activities and remember past events depending on the
presence of other people.
What . Interaction assumes knowledge about the user's action. Perceiving
and understanding human activities are very difficult tasks. Nevertheless,
a context-aware system has to face them to produce useful information.
Where . Spatial information is a relevant part of context, in particular, if it
is joined with temporal one.
When . Most of the context-aware applications do not use time. Changes that
take place over time are very interesting to understand human activity.
As an example, if a user spends very little time on a particular screenshot,
maybe the user is not interested in what is displayed. Moreover, actions that
are far from a particular behavioural model can be relevant for the system.
As an example, an interactive domestic environment should be aware of an
elderly person who does not take their medicines.
Why . Understanding why people perform actions is more and more difficult
than understanding what an action means. A good starting point is the use
of context information like body temperature, heartbeat and galvanic skin
reflex to obtain information about the emotional status of the user [3].
2.3.1 Context representations
Defining the notion of 'context' implies a model to represent it. Good general
representations of context do not exist, so the application designer has to
develop ad hoc schemes with limited capabilities to store and manage the
information described earlier. 'The evolution of more sophisticated represent-
ations will enable a wider range of capabilities and a true separation of
sensing context from the programmable reaction to that context' [3].
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