Database Reference
In-Depth Information
within a speci
c area. As soon as the sensors are found the node toolbox is updated
with the list of available sensor types (classes) that match the search criteria.
Each sensor node represents all the sensor instances of a particular sensor type that
are available at a speci
c location. When dragged into the workspace, the node encodes
the search criteria that were used for locating it into its embedded properties. By
dragging the appropriate sensor nodes into the workspace one can model graphs that
process similar data from different locations. A sensor node example and its properties
are shown on Fig. 4 . All available sensor attributes appear as output endpoints. The
node provides an additional input endpoint for connecting a selection
lter node. The
functions of this special node are described in the following paragraph.
Fig. 4. A sensor node and its properties
Selection Filter Nodes. In IoT applications it is sometimes desirable to process data
within a speci
lter node allows one to limit the data
records that will be processed using time-based criteria. Once connected to a sensor
node, the selection
c time window. The selection
lter node will expose its
recordTime
endpoint. This end-
point can be connected to a comparator node that describes
lter parameters.
Comparator Nodes. Comparator nodes can be connected to a selection
lter node to
de
ne a time-based
lter. Each node
'
s
lter parameters are exposed as node properties.
The following nodes are provided:
Between (date): Ensures that the processed records fall between two speci
c dates.
￿
Compare (abs. date): Ensures that the processed records satisfy the condition
recordTime operator userDate
￿
, where operator is a user-selected oper-
ator (less, less or equal, equal, greater or equal, greater) and
userDate a user-selected date.
Compare (rel. date): Ensures that the processed records satisfy the condition
(NOW - recordTime) operator value timeUnit
￿
, where operator is a
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