Location dependent data (LDD) is the data whose value is determined by the location to which it is related. In LDD system, caching is a crucial way to improve the performance because a new query can be partially answered locally when the client is continuously moving around. Semantic caching has been paid much attention in traditional database systems. However, the methods of semantic cache management proposed in those systems are not suitable for mobile computing environment. Moreover, although many improved semantic caching strategies for mobile computing application have been proposed in recent years, few papers discussed semantic cache coherence control, which is very important in mobile computing environment. In this paper, we propose PR-tree and HPIR based algorithm, which can significantly reduce the unnecessary uplink requests and downlink broadcasts compared to previous PIR based schemes. Simulation experiments are carried out to evaluate the proposed strategy.
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