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Sensors 2015, 15(3), 6105-6132; doi:10.3390/s150306105

In-Network Processing of an Iceberg Join Query in Wireless Sensor Networks Based on 2-Way Fragment Semijoins

School of Computer Science and Engineering, Chung-Ang University, Seoul 156-756, Korea
Academic Editor: Leonhard M. Reindl
Received: 11 October 2014 / Revised: 27 February 2015 / Accepted: 2 March 2015 / Published: 12 March 2015
(This article belongs to the Section Sensor Networks)
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Abstract

We investigate the in-network processing of an iceberg join query in wireless sensor networks (WSNs). An iceberg join is a special type of join where only those joined tuples whose cardinality exceeds a certain threshold (called iceberg threshold) are qualified for the result. Processing such a join involves the value matching for the join predicate as well as the checking of the cardinality constraint for the iceberg threshold. In the previous scheme, the value matching is carried out as the main task for filtering non-joinable tuples while the iceberg threshold is treated as an additional constraint. We take an alternative approach, meeting the cardinality constraint first and matching values next. In this approach, with a logical fragmentation of the join operand relations on the aggregate counts of the joining attribute values, the optimal sequence of 2-way fragment semijoins is generated, where each fragment semijoin employs a Bloom filter as a synopsis of the joining attribute values. This sequence filters non-joinable tuples in an energy-efficient way in WSNs. Through implementation and a set of detailed experiments, we show that our alternative approach considerably outperforms the previous one. View Full-Text
Keywords: iceberg join query; wireless sensor networks; sensor network database; 2-way fragment semijoin; optimal sequence of 2-way fragment semijoins iceberg join query; wireless sensor networks; sensor network database; 2-way fragment semijoin; optimal sequence of 2-way fragment semijoins
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Kang, H. In-Network Processing of an Iceberg Join Query in Wireless Sensor Networks Based on 2-Way Fragment Semijoins. Sensors 2015, 15, 6105-6132.

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