The threshold join algorithm for top-k queries in distributed sensor networks

In this paper we present the Threshold Join Algorithm (TJA), which is an efficient TOP-k query processing algorithm for distributed sensor networks. The objective of a top-k query is to find the k highest ranked answers to a user defined similarity function. The evaluation of such a query in a sensor network environment is associated with the transfer of data over an extremely expensive communication medium. TJA uses a non-uniform threshold on the queried attribute in order to minimize the number of tuples that have to be transferred towards the querying node. Additionally, TJA resolves queries in the network rather than in a centralized fashion, which minimizes even more the consumption of bandwidth and delay. Our preliminary experimental results, using our trace driven simulator, show that TJA is both practical and efficient. Copyright 2005 ACM.