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5.3. The Artifact-Based Approach
79
Grouping of artifacts describes how similar sensor readings from di erent ar-
tifacts are. The correlation coe cient of sensor pairs indicates the degree of
dependence. This has proven useful to define semantic proximity of devices
[
Antifakos and Schiele 2002
]
.
Rating, allows the alignment of multiple measurements on a one-dimensional
scale for comparison. This is implemented by a decision tree structure that
uses thresholds of various sensors as decision nodes.
Artifacts that execute sensor integration by one of the principles mentioned above
are regarded as setting leaders. They also act as gateways and communicate the
gathered results to the application layer. These functions are implemented on the
Smart-Its devices utilizing a basic message oriented communication. They are pro-
vided as a C include file for the CSS compiler. There is also a Java equivalent, for
cases where the functions are used on more powerful systems and in the back-end.
Application Layer
The application layer is the highest layer of the proposed model and accommodates
the main functionality of the application. It takes results from artifact and setting
layer and combines them to information directly useful to the application. In many
applications this means that the sensing information needs to be feed into some kind
of context model or a representation of the task at hand. Finally, the control of the
user interface is another eminent part of the application-layer. The application layer
can be implemented on a particular Smart-It, which is communicating with other
artifacts, or on standard hardware such as laptops or handheld computers, depending
on the characteristics of the application at hand. It communicates wirelessly with
the custom hardware of the enabled artifacts. In the next Section we present several
applications that were implemented using the artifact-based approach.
5.3.3 Case Studies/Evaluation
In this section we demonstrate the applicability and e ciency of the perception
model by means of various applications that have been implemented so far. The
artifact-based model fostered the development of the applications by its di erent
layers.
Proactive Instructions
This application, aims to overcome limitations of today’s printed instructions (see
Section 3.1). By means of a piece of flat-pack furniture it is demonstrated how
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