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With the emergence of high data rate sensor network applications, there is an increasing demand for high-performance query services. To meet this challenge, we propose Dynamic Conflict-free Query Scheduling (DCQS), a novel scheduling technique for queries in wireless sensor networks. In contrast to earlier TDMA protocols designed for general-purpose workloads, DCQS is specifically designed for query services in wireless sensor networks. DCQS has several unique features. First, it optimizes the query performance through conflict-free transmission scheduling based on the temporal properties of queries in wireless sensor networks. Second, it can adapt to workload changes without explicitly reconstructing the transmission schedule. Furthermore, DCQS also provides predictable performance in terms of the maximum achievable query rate. We provide an analytical capacity bound for DCQS that enables DCQS to handle overload through rate control. NS2 simulations demonstrate that DCQS significantly outperforms a representative TDMA protocol (DRAND) and 802.11b in terms of query latency and throughput.