a generic framework for monitoring continuous spatial queries over moving objects
DESCRIPTION
A Generic Framework for Monitoring Continuous Spatial Queries over Moving Objects. Outline. Introduction Related Work The Framework Overview Query Evaluation and Reevaluation Safe Region Computation Enhancements Performance Evaluation Conclusion. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
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A Generic Framework for Monitoring Continuous Spatial Queries over Moving Objects
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Outline
• Introduction• Related Work• The Framework Overview• Query Evaluation and Reevaluation• Safe Region Computation• Enhancements• Performance Evaluation• Conclusion
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Introduction
• With the advent of mobile and ubiquitous computing, monitoring continuous spatial queries over moving objects has become a necessity for various daily applications, such as fleet management, cargo tracking, child care, and location-aware advertisement.
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Introduction
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Introduction
• Existing studies on continuous query monitoring focused on reducing the evaluation cost only.
• The previous studies were designed to support specific query types only.
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Introduction
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Introduction
• The first monitoring scheme that addresses the location update issue.
• The framework is generic in the sense that it is not designed for a specific query type.
• The framework offers accurate monitoring results at any time.
• Query reevaluation in this framework is triggered by location updates only.
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Related Work
• Time-Parameterized R-Tree• STRIPES• Q-index• SINA
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The Framework Overview
• At the database server, all registered queries can be fit into main memory whereas not all the moving objects can.
• The database server handles location updates sequentially.
• The communication cost between every client and the database server is constant.
• Mobile clients are able to detect their locations
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The Database Server
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The Object Index
• The object index stores the current safe regions of all the objects.
• Since the safe region changes each time the object updates its location, the index should be optimized to handle frequent updates.
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The Query Index
• For each query, the database server stores: – The parameters of the query– The current query results– The quarantine area of the query
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Query Evaluation and Reevaluation
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Evaluating New Range Query
• Start from the index root and recursively traverse down the index entries that overlap the query rectangle until reaching the leaf entries where the safe regions are stored.
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Evaluating New kNN Query
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Evaluating New kNN Query
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Reevaluating Range and kNN Queries
• The incremental reevaluation of an affected range query is straightforward.
• For an order-sensitive kNN query, there are three cases in reevaluation:– 1) p is not in the quarantine area, but plst is; – 2) p is in the quarantine area, but plst is not; – 3) both p and plst are in the quarantine area.
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Safe Region Computation
• The safe region of a moving object p designates how far p can reach without affecting the results of any registered query.
• The safe region for a query Q is the rectangular region in which p does not affect Q’s result.
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Safe Region Computation
• The server needs to re-compute the safe region of an object p in three cases: – During the evaluation of a new query Q– After processing a source-initiated location
update of object p– During the processing of a source-initiated
location update
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Safe Region Computation
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Safe Region for Range Query
• If Q is a range query and p is in its quarantine area, the safe region is simply the quarantine area itself.
• Otherwise, there are four possible rectangles within the cell that can serve as the safe region, each of which has one of its sides coincide with a side of the cell.
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Safe Region for kNN Query
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Safe Region for a Batch of Range Queries
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Enhancements
• The object always moves steadily towards its destination, in other words, it follows a rough direction for a significantly long period of time.
• Each object is limited by a maximum moving speed.
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Maximum Speed for Query Evaluation
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Steady Movement for Safe Region Computation
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Performance Evaluation
• Safe-Region-Based query monitoring (SRB) framework.
• Optimal monitoring (OPT)• Periodic monitoring (PRD)
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Simulation Setup
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Impact of Communication Delay
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Scalability
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Scalability
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Sensitivity of SRB
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Sensitivity of SRB
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Performance of the Enhancements
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Conclusion
• The framework distinguishes itself from existing work by being the first to address the location update issue and to provide a common interface for monitoring mixed types of queries.