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Chapter 5. General Concepts, Toolkits, and Frameworks
di erent scenarios we also encounter settings where group membership changes in
an ad-hoc fashion and communication is only available at certain points in time and
space.
The main task performed in the settings layer is to combine information gathered
from individual artifacts to meaningful collective context information in the setting.
The integration of sensor data across artifacts and in more general data fusion over
perception information provided by the artifact-layer leads to setting primitives.
These primitives represent the context information of the particular setting and are
higher-level abstractions of combined observations. The output of the settings layer
is therefore the setting context. Similar to the artifact layer it also provides access
to the settings history.
Application Layer
On the application layer loosely and potentially ad-hoc connected and cooperating
settings are considered. In this layer the application that uses context is located.
The context is collected from settings from the layer below.
For a particular application in the application layer it is of interest which settings are
relevant and how the settings are related. The outputs of the settings, abstracted
representations of the world modeled in the setting, become the basis for the per-
ception in the application layer. Based on the perception primitives provided by
the settings, the application layer performs recognition tasks that are required by
an application.
The participation of a particular setting in a number of applications introduces a po-
tential source for conflicts. The resources within a setting, e.g. which primitives are
calculated, at which rate perception is performed, and which information is bu ered,
must then be shared between applications. It can be assumed that applications are
cooperative, but for large scale scenarios the conflict resolution or avoidance has to
be included in the settings layer.
The communication between the application and the underlying settings is a central
issue. The general case is that communication is available in an ad-hoc fashion and
that there is no guarantee that all settings are always accessible. In many cases the
application can define a minimal core group of setting primitives that are required
to ensure useful operation. The application is operational as soon as these settings
are available. If more setting primitives become available the context awareness of
the application may become better.
The central task in the application layer is to combine perception primitives of
settings into meaningful context. This is realized by fusing perception data across
settings, which is of particular interest to an application. The calculated context is
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