Two-Phase Top-k Query Processing in Mobile Ad Hoc Networks

In mobile ad hoc networks (MANETs), to acquire only necessary data items, it is effective that each mobile node retrieves data items using a top-k query, in which data items are ordered by the score of a particular attribute and the query-issuing mobile node acquires data items with k highest scores. In our previous works, we proposed query processing methods for top-k query for reducing traffic and also keeping high accuracy of query result. However, those methods have the problem that reduction of candidates included in the top-k result is still not enough because nodes cannot know the accurate k-th highest score. In this paper, we propose a two-phase query processing method for top-k query processing. In this method, the query-issuing node collects the information of scores of data items held by each node in the first phase. Based on the received information, it determines the threshold of the score, i.e., the estimated k-th highest score. Then, in the second round, the query-issuing node transmits a query attached with the threshold, and each node that received the query sends back only its own data items whose scores are equal to or larger than the threshold. In this way, our proposed method can further reduce the traffic and also keep high accuracy of the query result.