Information Technology Reference
In-Depth Information
as smoke limit and 353 Kelvin (80 centigrade)
as the ambient temperature limit. Whereas the
existence of carbon monoxide is a good stand-
alone indicator for fire, temperature and smoke
readings should be suitably combined to gain a
higher false alarm resistance. Therefore, smoke
and temperature thresholds are linked using a
logical AND and are combined with the carbon
monoxide threshold using a logical OR. Hence,
an event
fire
is detected if either the carbon
monoxide readings exceed 100 ppm OR both
smoke AND temperature readings exceed their
assigned thresholds. In case of having evaluated
the phenomenon
fire
to exist, the sensor node
triggers the
sendalert
event handler. A radius of
2.5 meters around the sensor nodes is assumed
a reasonable collaboration region for distributed
detection. Hence, the dimension element defines
that region as a ball specifying a maximum radius
of 2.5 meters.
The event specification generator creates
hardware-specific binary event specifications of
universally valid event specifications. It is obvi-
ous, that general event specifications cannot be
uniformly transferred to every sensor platform
due to different hardware and software properties.
To overcome these problems introduced by per-
vasiveness and heterogeneity, the event specifica-
tion generator adapts variables, thresholds, han-
dlers, phenomenon constraints etc. to the target
sensor platform regarding expected hardware,
sensing capabilities and the available OS. After-
wards, the elements in the adapted event specifi-
cation are substituted by symbols and compressed
into the final minimized binary event specifica-
tion, which can then be used for configuration.
All mentioned steps are fully-transparent to the
user and automatically done by the event speci-
fication generator. That allows to keep the event
definition process quite simple and intuitive by
decoupling it from the configuration process.
The ESL event specification generator is
written in Java to enable execution on different
devices and platforms providing a Java Virtual
Machine (JVM). In particular, we focus on mo-
bile devices like laptops or smartphones. This
provides the necessary mobility for envisioned
applications in pervasive technologies. The
integrated hardware abstraction layer interface
enables to implement the mentioned adaptation to
meet the requirements of target sensor platform.
More precisely, this interface provides a couple
of functions for harmonization of general ESL
elements. These functions process the elements
that need to be adapted to hard- and software spe-
cifics and return the customized variants. Hence,
each sensor platform only needs to provide a
suitable implementation of this interface to gain
compatibility to the introduced event configura-
tion system. That allows to easily create different
hardware-specific binary event specifications for
deployment on various platforms. To simplify
matters, the following presents the generation of
the binary event specification for the introduced
Generation of Deployable Binary
Event Specifications
Event specifications provide flexible and easy-to-
use configuration means for using sensor networks
beyond the scope of research, even for non-experts
in the field such as medical employees adapting
them for customized patient monitoring. However,
XML is oversized for direct use on sensor nodes,
which are subject to strict energy and memory
constraints. To minimize the calculation effort on
the sensor nodes as well as to minimize the amount
of data to be transferred, event specifications are
pre-parsed to generate smaller versions before in-
network deployment. These compacted versions
are called binary event specifications. Binary event
specifications are applied for initial configuration
as well as for updates, i.e., reconfiguration or
deletion of configured event specifications. This
section presents implementation details and the
workflow of the event specification generator,
which is depicted in Figure 5.
Search WWH ::
Custom Search