Correct execution of continuous monitoring queries in wireless sensor systems

Two important objectives in processing a continuous monitoring queries (CMQ) are: (1) to minimize the processing overheads, especially in communication and query evaluation; and (2) to provide temporally consistent sensor data for query evaluation. The first one is important to normal operations of sensor devices while the second one is to ensure the correctness of the query results. We propose periodic pushing schemes, called PerPush and ConPush, to aggregate the subquery results of a CMQ. To further improve the performance, we propose the Sequential Pushing (SeqPush) scheme for aggregating the sensor data values generated by the sensor nodes which are close to each other. The pushing path in SeqPush follows a sequential pattern according to the semantic of the queries and the results of evaluation of the subqueries at the nodes participating in the CMQ.