A Proxy-Based Approach to Continuous Location-Based Spatial Queries in Mobile Environments
Caching valid regions of spatial queries at mobile clients is effective in reducing the number of queries submitted by mobile clients and query load on the server. However, mobile clients suffer from longer waiting time for the server to compute valid regions. A proxy-based approach is proposed to continuous nearest-neighbor (NN) and window queries. The proxy creates estimated valid regions (EVRs) for mobile clients by exploiting spatial and temporal locality of spatial queries. For NN queries, two new algorithms is implemented to accelerate EVR growth, leading the proxy to build effective EVRs even when the cache size is small. EVRs of window queries is posed in the form of vectors, called estimated window vectors (EWVs), to achieve larger estimated valid regions. This novel representation and the associated creation algorithm result in more effective EVRs of window queries. In addition, due to the distinct characteristics, separate index structures are used, namely EVR-tree and grid index, for NN queries and window queries, respectively. The experimental results show that the proposed approach significantly outperforms the existing proxy-based approaches.