processing monitoring queries on mobile objects lecture for coms 587 department of computer science...

Processing Monitoring Queries on Mobile Objects

Lecture for COMS 587

Department of Computer Science

Iowa State University

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

Characteristics

Large number of mobile objects

Continuous movement of mobile objects- Limited battery power

- Limited communication bandwidth

Processing Range-Monitoring Query

• What is range-monitoring query?

– Retrieve mobile objects in a spatial region, and

– continuously monitor the population in the area

Range-Monitoring Queries

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Range-Monitoring Queries

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Tourist guiding

Automatic traffic control

Digital battlefield vehicle tracking

Wild animal tracking

Some Potential Applications

How to minimize location updates?

– Excessive mobile communication could

drain battery power quickly

How to minimize server processing

cost?

– Query results keep changing

Research Issues

Related Works

Location Estimation [Woflson98, Woflson99, etc.]

Trajectory Indexing [Kollios99, Saltenis00, etc.]

Safe Region Approach [Prabhakar00, Prabhakar01]

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Q5

Q2

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Safe Regions

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Circular Safe Region

RectangularSafe Region

a

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

How to provide

– accurate query results,

and

– real-time updates?

Challenge

Proposed: Monitoring-Query Management

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Resident Domain

Given an object’s position P and its

processing capability N, its resident

domain should

Computing a Resident Domain

– contain position P, and

– be as large as possible, but

– contain no more than N queries

Domain and Query Decomposition

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R1

R42

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Domain and Query Decomposition

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R42

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Domain Tree (D-tree)

D

D domain node

data node

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d1

d1 d2d2


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d1 d2d21

d22

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D


Mobile Communication Cost

0

5

10

15

20

25

30

10 20 30 40 50 60 70 80 90 100Num

ber

of

mes

sage

s se

nt

by m

obile

obj

ects

(m

illio

ns)

Number of monitoring queries (thousands)

MQM

Safe Region

Server Processing Cost

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1

10

100

1000

10 20 30 40 50 60 70 80 90 100Num

ber

of in

dex

node

s ac

cess

ed (

mill

ions

)

Number of monitoring queries (thousands)

MQMSafe Region

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

Mobile Range Monitoring Queries (M-RMQ)

A M-RMQ retrieves the mobile

objects within a range

centered on a mobile object

It is associated with a mobile

object called focal node

The movement of the focal

node and other mobile

objects may lead to the

change of query results

Proposed: MobiEye

The network domain is divided into a number of grid cells

Each focal node reports its velocity to the server and update when such information changes

Each query window is associated with a bounding box

All nodes within a bounding box are notified of the velocity of the query

When a node detects that its moves into/out of a bounding box, report to the server

Decentralized Mobile Database Management

Mobile ad hoc networks A set of mobile objects form a

network by themselves The communications among

these objects are done through packet relaying Without relying on any fixed

infrastructures Low cost and easy setup (great

for battlefields)

Many protocols have been developed for efficient routing discovery and communications

a

bcf

d

e

g

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Handling Stationary Range Monitoring Queries

Key research issue: where the queries are stored Solution 1: each node keeps a

copy of each query Great for query evaluation Expensive for query installation

and removal

Solution 2: each node keeps only the queries it issues Great for query installation and

removal Expensive for query evaluation

a

bcf

d

e

g

h


Network partitioning

Each node caches all queries relevant to its home cell

While moving inside a cell, a node monitors its movement against the queries it knowsif crossing over any

boundary, update the query issuer

What happens when moving into/out of a cell?


When moving out of its cell, a node checks if it is the last node No - remove the queries

Yes – keep the queries, the node becomes the retaining node to the cell

When moving into a new cell, a node retrieves the new relevant querieseither from any node in the cell,

or

from the cell’s retaining node


Searching for a retaining node can be done by expanding the search range step by step

A cell’s retaining node may move far away from the cell Keep the queries in a node

that is close to the cell

Compute the distance whenever moving into a new cell, and if necessary, unload the queries to some nearby node

Handling Mobile Range Monitoring Queries

Handling Mobile Range Monitoring Queries

Concept of safe boundary

Handling Stationary KNN queries

Handling Mobile KNN queries

Questions

Any other types of queries?Can any type of queries be converted

into one or more stationary range monitoring queries?

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