Efficient Valid Scope Computation for Location-Dependent Spatial Queries in Mobile and Wireless Envi...
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Efficient Valid Scope Computation for Location-Dependent Spatial Queries in Mobile and Wireless Environments. Ken C.K. Lee, Wang-Chien Lee, Hong Va Leong, Brandon Unger and Baihua Zheng, ICUIMC’09 Manu Shukla August 2, 2009. Introduction.

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Efficient Valid Scope Computation for Location-Dependent Spatial Queries in Mobile and Wireless Environments

Ken C.K. Lee, Wang-Chien Lee, Hong Va Leong, Brandon Unger and Baihua Zheng, ICUIMC’09

Manu Shukla

August 2, 2009


Introduction
Introduction Spatial Queries in Mobile and Wireless Environments

  • Mobile clients access information with respect to their location by submitting Location Dependent Spatial Queries (LDSQ) to Location-Based service servers

  • Due to limited mobile bandwidth and limited client battery life, frequent LSDQ submission must be avoided

  • Authors define the concept of valid-scope, a spatial area in which a set of LSDQs will retrieve exactly the same query results

  • Propose algorithms for valid scope computation for common LDSQs like range query and NN query


Valid scope
Valid Scope Spatial Queries in Mobile and Wireless Environments

  • Determine a small and representative subset of non-result objects called “complementary objects” together with result objects

  • Use R-tree and best first search


Valid scope for nn query
Valid Scope for NN Query Spatial Queries in Mobile and Wireless Environments

  • Objects that contribute the bisector as voronoi cell perimeter are added to complementary objects

  • Exploit the largest empty circle property


Nn query
NN Query Spatial Queries in Mobile and Wireless Environments

  • Two steps to determine the NN query result and the valid scope of the result and one index lookup

    • First retrieve the nearest object

    • Examine non-result objects to refine valid scope


Valid scope for knn query
Valid Scope for kNN Query Spatial Queries in Mobile and Wireless Environments


Valid scope for range query
Valid Scope for Range Query Spatial Queries in Mobile and Wireless Environments

  • Minkowski region is defined as

  • Valid Scope is computed as an area equal to the intersection of the Minkowski regions of all result objects


Range query
Range Query Spatial Queries in Mobile and Wireless Environments

  • Formula for valid scope can be defined as


Experiments
Experiments Spatial Queries in Mobile and Wireless Environments

  • Compared with time-parameterized query method by Zhang et.al

  • Three data sets, real and two synthetic based on Gaussian and Uniform distribution


Experiments1
Experiments Spatial Queries in Mobile and Wireless Environments

  • Overhead incurred by valid scope computations


Conclusions
Conclusions Spatial Queries in Mobile and Wireless Environments

  • Valid for spatial queries in mobile environment where bandwidth and battery power in mobile devices are limited

  • Most calculations done on server and hence scalable


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