Processing Monitoring Queries on Mobile Objects

1. Processing Monitoring Queries on Mobile Objects CS461 Lecture Department of Computer Science Iowa State University

2. What is a mobile database? • A mobile database is a set of mobile devices • Centralized: there exists a central server with which each mobile device can communicate • Decentralized: these devices form a network by themselves • Mobile ad hoc network (MANET) • Mesh networks

3. Characteristics • Large number of mobile objects • Continuous movement of mobile objects • Limited battery power • Limited communication bandwidth

4. Processing Range-Monitoring Query • What is range-monitoring query? • Retrieve mobile objects in a spatial region, and • continuously monitor the population in the area

5. Range-Monitoring Queries Q2 a d e Q1 c b f

6. Range-Monitoring Queries Q2 a d Q1 e b c f

7. Some Potential Applications • Tourist guiding • Automatic traffic control • Digital battlefield vehicle tracking • Wild animal tracking

8. Research Issues • How to minimize location updates? • Excessive mobile communication could drain battery power quickly • How to minimize server processing cost? • Query results keep changing

9. Related Works • Location Estimation [Woflson98, Woflson99, etc.] • Trajectory Indexing [Kollios99, Saltenis00, etc.] • Safe Region Approach [Prabhakar00, Prabhakar01]

10. Safe Regions Rectangular Safe Region Q1 Q2 Q5 a Q3 Q4 Circular Safe Region

11. Problems with Safe Regions • Computing a safe region takes from O(n) to O(n log3 n) • Adding a new query requires to re-compute safe regions for all objects

12. Challenge How to provide • accurate query results, and • real-time updates?

13. Proposed: Monitoring-Query Management Q1 Q6 Q3 Q2 a Q5 Q7 Q4 Resident Domain

14. Computing a Resident Domain • Given an object’s position P and its processing capability N, its resident domain should • contain position P, and • be as large as possible, but • contain no more than N queries

15. Domain and Query Decomposition Q2 Q3 R1 R21 R22 Q1 R31 Q4 R41 R42

16. Domain and Query Decomposition Q2 Q3 R1 R21 R22 Q1 R31 a Q4 R41 R42

17. Domain and Query Decomposition Q2 Q3 R1 R21 R22 Q1 R31 a Q4 R41 R42

18. Domain Tree (D-tree) D domain node D data node

19. Domain Tree (D-tree) D d1 d2 d1 d2

20. Domain Tree (D-tree) D d21 d1 d2 d1 d21 d22 d22

21. Mobile Communication Cost 30 25 20 Safe Region 15 Number of messages sent by mobile objects (millions) MQM 10 5 0 10 20 30 40 50 60 70 80 90 100 Number of monitoring queries (thousands)

22. Server Processing Cost 1000 100 Safe Region 10 MQM Number of index nodes accessed (millions) 1 0.1 10 20 30 40 50 60 70 80 90 100 Number of monitoring queries (thousands)

23. Significant and Impact of MQM • MQM is the first scalable technique, in terms of mobile communication and server processing costs, for real-time range-monitoring query management

24. Questions • Any other types of queries? • Can any type of queries be converted into one or a number of range monitoring query?