Similarly, a query also uses the name of the data to acquire the
location where the data is stored and the query is sent to that sensor.
A
C B
D
Fig. 4. Data centric storage algorithm [16].
Besides data centric storage, we consider two alternatives: an External
Storage scheme in which all events are stored at a node outside the network;
and a Local Storage scheme where each event is stored at the node at which
it is generated.
For external storage, the cost of accessing events is zero, since all events are
available at one node. However, the cost of transporting data to this external
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Chapter 12 Data Management in Sensor Networks
node is non-trivial; there is an energy cost in sending events to this node, and
significant energy is spent at nodes near the external node in receiving all
these events (these nodes become hot-spots). If events are accessed far more
frequently than they are generated, external storage might be an acceptable
alternative (assuming the event generation rate does not form the bottleneck).
At the other end of the spectrum, local storage incurs zero communication cost
in storing the data, but incurs a large communication cost, a network flood,
in accessing the data. Local storage may therefore be feasible when events
are accessed less frequently than they are generated. Data-centric storage lies
somewhere in between, since it incurs a non-zero cost both in storing events
and retrieving them.
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