Database Reference
In-Depth Information
in question. Hence, in practice, out-of-order POG may be delayed but
would not arrive prematurely. Clearly, such delay or even complete loss
of a POG would not cause any errors (such as incorrect purge of the
operator state), rather it would in the worst case cause increased output
latency. Fortunately, no incorrect results will be generated because the
WinNeg operator would simply keep blocking until the subsequent POG
arrives.
5. Conclusions and Summary
Sensor streams generated from sensor and RFID applications provide
rich observations of physical objects. Event based processing of sensor
data enables tracking and monitoring of physical objects and seman-
tically interpreting complex event patterns. Event processing engines
are essential to provide effective, ecient, and near real-time complex
event processing of sensor data streams. Driven by the semantics of
sensor events and event processing, and example use cases, we discuss
two scenarios on event processing: event processing in sensor networks
and event processing in RFID applications. For event processing in sen-
sor networks, we present three major categories of approaches: statisti-
cal methods, topographical techniques, and edge detection algorithms.
RFID events have their unique characteristics, and we discuss event
specification languages, event detection models, event processing meth-
ods and their corresponding optimizations. Finally, we discuss two major
challenges in practice, the effect of event uncertainty and the disorder of
events.
References
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[2] Liu, Y., Li, M.: Iso-map: Energy-ecient Contour Mapping in Wire-
less Sensor Networks. ICDCS, pp. 36-44. (2007)
[3] Li, M., Liu Y., Chen, L.: Non-threshold Based Event Detection for
3d Environment Monitoring in Sensor Networks. ICDCS. (2007)
[4] Li, M., Liu, Y.: Underground Structure Monitoring with Wireless
Sensor Networks. IPSN. (2007)
[5] Chintalapudi, K. K., Govindan, R.: Localized Edge Detection in
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