February 4, 2002 1

Location Based M-Services Soon there will be more on-line personal mobile devices than on-line

stationary PCs. Location based mobile-services

Moving users equipped with mobile phones, PDAs, etc., periodically disclose their positions to the service provider

The service provider tracks the movement of the users and provides useful services: “If you want to get home faster today, do not turn into street X (where you will get into a traffic

jam)” “On the right, you should see the Smithsonian Air and Space Museum – the museum you should

definitely visit before leaving Washington D.C.”

February 4, 2002 2

LBS Architecture

Service providerDBMS

Locationsof users

Maps,other info

Data structures

PositioningLocation info

Service requests (queries)

Services (location-specific, on-time, personalized information)

February 4, 2002 3

1.Reducing the Update-Load

In LBS scenarios and in other pervasive computing scenarios (e.g., sensor nets) one of the problems is a high load of updates A million objects, each reporting its position once a

minute: Too high communication loads A database may not be able to keep up (We want to handle

as much as possible updates using a centralized database) If objects move completely randomly and we want to

have very precise positions, not much can be done. In the real world:

Objects move “orderly” We may be satisfied with reduced accuracy

February 4, 2002 4

1.Reducing the Update-Load

Let the database have a much richer knowledge about the future predicted movement of objects and let the objects know what the database “assumes”:

No matter how a road is twisted, if I move with a constant velocity on this road and the database knows the map of roads and my velocity, there is no need to keep reporting my position to the database

Allow for lazy updates. Two step query processing: retrieve a larger candidate set, ask each of the objects to report its latest position, and check if it really satisfies the query

The goal of the project would be to develop and evaluate these techniques assuming a specific type of data (e.g., positions of moving cars)

February 4, 2002 5

2.Indexing in Oracle Indexes are data structures that

support fast answers to queries Commercial ORDBMSs support indices

for static spatial data: “Find gas stations close to me”

No support for the indexing of continuously moving objects: “Find customers close to my gas station”

February 4, 2002 6

2.Indexing in Oracle The goal of the project – to implement and

compare a number of alternatives for how to index moving objects in Oracle: One could view moving objects represented by

(x,y,vx,vy) as four dimensional moving points and index them with the built-in spatial index

One could try to use Oracle index-extensibility interface and implement a new index specifically for continuously moving points

February 4, 2002 7

3.Managing Traffic using DB

The goal of this project would be to investigate a specific application area – traffic management using on-line vehicles: I want to maintain an overview (and possibly

record a history of) the current traffic situation – an approximate number of vehicles on each segment of any road

I need to maintain this aggregate information in the database, not enough just to have possitions of objects

I want to ask “shortest-path” queries, that take into account traffic information

February 4, 2002 8

3.Managing Traffic using DB

Two directions for the project: More theoretical (what kind of external

data structures are needed, how external algorithms, e.g., graph algorithms, work)

More practical – again, take Oracle and look how much we can squeeze out of it to implement the desired functionality

February 4, 2002 9

Realistic Data for Experiments

Data from the tracking of a number of test cars in Aalborg.

Moving object data generated with IBM's City Simulator

February 4, 2002 10

Contact Simonas Šaltenis and Michael

Böhlen Mike is not at the university this week

E1-215b and E1-215 simas@cs.auc.dk, boehlen@cs.auc.dk