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Figure 7. Detailed architecture of the EDT-engine
later in this section. Finally, the timer of the EDT
is set up to the next evaluation interval and the
EDT is returned to the EDT scheduler. In addition
to the configured evaluation interval, EDTs are
also triggered on demand by collaboration requests
from other devices. In that case, evaluation of the
EDT is executed as usual but consequently answers
the request, too. After finishing an unscheduled
evaluation, the corresponding timer is reset to a
full detection interval. On the one hand, that as-
sures a sufficient detection interval as required
by the event specification. On the other hand, it
simultaneously reduces the number of evaluation
processes to a certain minimum to save energy
resources.
based on a tiny Generating Finite State Machine
(GFSM) with eight states. That enables to imple-
ment the EDT generator on almost every available
sensor platform. In the simulator the implementa-
tion of the GFSM required only 25 lines of C/C++
code. The EDT generator transforms the prefix
notation of the sensor data element into a congruent
representation as an EDT. Leaf nodes identifying
sensing capabilities or constant values according
to the specification of thresholds provide the basis
for EDTs. Leaf nodes are child nodes of relational
or algebraic elements. Algebraic nodes define al-
gebraic operations between its child nodes. On top
of leaf nodes or algebraic nodes, relational nodes
constitute the respective relation between its two
children. These minimal trees of three nodes are
primitive events. In complex events they become
respective subtrees.
Logic nodes, representing the logic combina-
tions of several primitive events, are generated
as parent nodes on top of relational elements. In
the fire detection example, the root node of the
EDT represents a Boolean OR-relation between
Establishing Event Decision Tree
Binary event specifications are parsed at the sensor
nodes to generate evaluable event configurations
by establishing EDTs. These represent the phe-
nomenon based on the sensor data element of the
binary event specification. The EDT generator is
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