Database Reference
In-Depth Information
Executing In-network Queries Using SNEE
Ixent Galpin, Robert Taylor,
Alasdair J.G. Gray, Christian Y.A. Brenninkmeijer,
Alvaro A.A. Fernandes, and Norman W. Paton
School of Computer Science, University of Manchester, UK
{ixent,a.gray,brenninkmeijer,alvaro,norm}@cs.man.ac.uk
Keywords:
Wireless Sensor Networks, In-network Processing, Distributed
Query Processing, Stream Query Languages.
The
SNEE
query optimizer enables users to characterize data requests against
wireless sensor networks
(WSNs), using a declarative query language called
SNEEql
(
SNEE
for
S
ensor
NE
twork
E
ngine, described in [GBG
+
11], and publicly
perative
query execution plans
, which are translated into executable
nesC
source
code
1
. In this paper, we illustrate the lifecycle of a
SNEEql
query
Q
for in-network
execution. This lifecycle encompasses the steps of preparatory metadata collec-
tion, followed by the compilation of
Q
into a query execution plan
QEP
,the
dissemination of binary images implementing
QEP
throughout the WSN, and
the generation of query results.
To demonstrate our approach, we monitor light in a building using a simple
3-node WSN, depicted in Fig. 1, comprising of
Te l osB
motes
2
.InourWSN,
node 1 is the
gateway
node (i.e., the node from which commands and query
execution plans are disseminated to the WSN, and also where query results are
collected), and nodes 2 and 3 monitor light levels for the upstairs and down-
stairs areas of the building respectively. The schema comprises three logical
streams,
building, upstairs
and
downstairs
,oftype
(id:int, time:int,
light:int)
.The
building
stream is the union of the
upstairs
and
downstairs
streams.
The example queries that we use to illustrate our approach are shown in
Fig. 2. Query (a) requests all the light readings in the building; (b) requests the
average value of the light readings in the building; and (c) requests light readings
when the light level upstairs is higher than downstairs (i.e., it may indicate that
someone has forgotten to switch off a light). The QoS expectations are both
an
acquisition interval
and
delivery time
of 10s (i.e., query results need to be
delivered before the next tuple is acquired).
2
This hardware has the following specification: CPU = MSP430 8MHz, RAM =
10 kB, Program Memory = 48 kB, Data Flash = 1 MB, Radio = CC2420. Detailed
