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A Proxy-Based Approach to Continuous Location-Based Spatial Queries in Mobile Environments

机译:移动环境中基于连续位置的空间查询的基于代理的方法

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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. We propose in this paper a proxy-based approach 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, we devise two new algorithms to accelerate EVR growth, leading the proxy to build effective EVRs even when the cache size is small. On the other hand, we propose to represent the EVRs of window queries 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, we use separate index structures, namely EVR-tree and grid index, for NN queries and window queries, respectively. To further increase efficiency, we develop algorithms to exploit the results of NN queries to aid grid index growth, benefiting EWV creation of window queries. Similarly, the grid index is utilized to support NN query answering and EVR updating. We conduct several experiments for performance evaluation. The experimental results show that the proposed approach significantly outperforms the existing proxy-based approaches.
机译:在移动客户端缓存空间查询的有效区域可有效减少移动客户端提交的查询数量和服务器上的查询负载。但是,移动客户端需要等待服务器计算有效区域的时间更长。我们在本文中提出了一种基于代理的方法来进行连续最近邻(NN)和窗口查询。代理通过利用空间查询的空间和时间局部性为移动客户端创建估计的有效区域(EVR)。对于NN查询,我们设计了两种新算法来加速EVR的增长,即使高速缓存很小,代理也可以构建有效的EVR。另一方面,我们建议以向量的形式来表示窗口查询的EVR,称为估计窗口向量(EWV),以实现更大的估计有效区域。这种新颖的表示形式和相关的创建算法可产生更有效的窗口查询EVR。另外,由于其独特的特性,我们分别对NN查询和窗口查询使用单独的索引结构,即EVR树和网格索引。为了进一步提高效率,我们开发了算法以利用NN查询的结果来帮助网格索引增长,从而有利于EWV创建窗口查询。类似地,网格索引用于支持NN查询应答和EVR更新。我们进行了几项性能评估实验。实验结果表明,该方法明显优于现有的基于代理的方法。

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