Data Retrieval Mechanisms in Mobile Environments by Using Spatial Queries

This work discusses a novel hybrid replacement policy to adopt in the design of our cache. According to our hybrid caching strategy, the results of the most frequently accessed queries are maintained in a static cache of fixed size, which is completely rebuilt at fixed time intervals. Only the queries that cannot be satisfied by the static cache compete for the use of a dynamic cache. Our hybrid cache represents an effective and fast way to address both recency, and frequency of occurrences criteria. While the static cache maintains results of queries that are globally frequent, a simple and fast policy like LRU, which only takes into account query reference recency,could be adopted for the dynamic cache. This novel representation and the associated creation algorithm result in more effective EVRs of window queries. In addition, due to the distinct characteristics, a separate index structures, namely EVR-tree and grid index, for NN queries and window queries, respectively are used. To further increase efficiency, an algorithms to exploit the results of NN queries to aid grid index growth, benefiting EWV creation of window queries is developed. Similarly, the grid index is utilized to support NN query answering and EVR updating. Several experiments for performance evaluation are performed. The experimental results show that the proposed approach significantly outperforms the existing proxy-based approaches.