High Level Definition of Event-Based Applications for Pervasive Systems - Advanced Design Approaches to Emerging Software Systems - page 131

BACKGROUND the design flow of application programming is here

tailored to user needs. In such a user-centric design
flow, the user only needs to describe the physical
phenomenon to be sensed without regard to WSN
properties. The major goal is to allow users to
define applications by a generally valid descrip-
tion of the “things” to be sensed (phenomenon),
as it is exemplified in Figure 1. All further steps
required for configuration and adaption of these
applications to a certain WSN remain fully trans-
parent to the user. The sensor nodes autonomously
configure to a generally defined task description
given by the user. Therefore the user can specify
a physical phenomenon via a GUI by defining the
required sensing features, the spatial and temporal
resolution and the actions to be triggered. Based
on that, an event specification generator expresses
a description of the phenomenon to be detected in
an intuitive XML-dialect. This event specification
is automatically adapted to the requirements of the
target platform. Finally, a minimized deployable
event specification is disseminated within the
sensor network. The sensor nodes autonomously
configure to the received event specification.

Traditional sensor network applications report all
sensor readings to a global sink either continuously
or if certain conditions are met. Sinks are usually
special nodes that provide more resources and
make the final decision about sensed phenomena
based on received readings. Such data gathering
applications exchange extensive amounts of data,
cause much traffic and consume much energy.
Hence, they reduce lifetime, throughput and re-
sponsiveness of the network. Thus, only certain
changes in sensor readings, called events, shall
be transmitted. Events provide a suitable abstrac-
tion of real world phenomena, whose physical
properties can be measured by sensors (Romer
& Mattern, 2004). Events typically describe a
number of measurement related constraints, e.g.,
thresholds of sensor readings. Sensors fire an event
if current measurements indicate the exceedance
of these thresholds. Fired events usually trigger
further actions, such as the activation of alarms or
the recording of detailed data for further analysis.

Figure 1. User-centric application design allows abstraction of the task definition process from WSN-
related properties and internal configuration processes. The user merely specifies the phenomenon to
be sensed, which is then autonomously configured to the desired target sensor platform.