Minkyoon Kim, Sangjin Han1 Querying in Highly Mobile Distributed Environments T.Imielinski and B. R. Badrinath Minkyoon Kim Sangjin Han

Minkyoon Kim, Sangjin Han2 Base Stations and Cells Base station Cell

Minkyoon Kim, Sangjin Han3 Hierarchical Structure of Cellular Network Location Server Base Server Mobile Unit Public Access Network (PSTN, Internet, …) Radio Link

Minkyoon Kim, Sangjin Han4 Location Information As a Database

Minkyoon Kim, Sangjin Han5 Queries What We Desire Where’s Alice? Where is the nearest doctor?! Find me the best route to the…

Minkyoon Kim, Sangjin Han6 Control of Update Volume Cell 1 Cell 2 How can we maintain locations of all users?

Minkyoon Kim, Sangjin Han7 Updates Principle: Do not tell me if I do not want to know

Minkyoon Kim, Sangjin Han8 Three Strategies for Locating Users Broadcast List Partition Total cost is “Update Cost” + “Locating Cost”  Response time is not considered here.

Minkyoon Kim, Sangjin Han9 Broadcast

Minkyoon Kim, Sangjin Han10 List

Minkyoon Kim, Sangjin Han11 Pointer

Minkyoon Kim, Sangjin Han12 Simulation Model

Minkyoon Kim, Sangjin Han13 Simulation Results of Three Strategies

Minkyoon Kim, Sangjin Han14 Main problem arising from query processing How to minimize the communication cost to answer the query?

Minkyoon Kim, Sangjin Han15 Naïve strategy of query processing Find objects satisfying constraints on individual objects Determine exact locations of each object by paging the partition of each object Check if the result satisfies the constraints on locations of the objects

Minkyoon Kim, Sangjin Han16 Query Example Give the names of doctors located near Kim’s current location {d| Near(d.loc, Kim.loc) and Doctor(d)} For all doctors, check if Kim and the doctor is nearby Kim

Minkyoon Kim, Sangjin Han17 Naïve Strategy a partition of the doctor’s profile a partition of Kim’s profile Page both partitions Determine whether the actual positions of a doctor and Kim is “near by”

Minkyoon Kim, Sangjin Han18 Another Strategy First determine whether paging is required at all If paging is required, there’re two choices  page U first or page V first? a partition of the doctor’s profile a partition of Kim’s profile U V

Minkyoon Kim, Sangjin Han19 Paging order matters! If we page U first, paging V is not necessary If we page V first, paging U is required. U V

Minkyoon Kim, Sangjin Han20 *** Classification Tree Here

Minkyoon Kim, Sangjin Han21 Minimal communication cost strategy Strategy means  the sequence in which we will page partitions How hard is it to find an optimal strategy?  NP-complete

Minkyoon Kim, Sangjin Han22 Open problems in the mobile environment

Minkyoon Kim, Sangjin Han23 More refined cost model The total time necessary to broadcast all paging messages Queried object may reside in the same area

Minkyoon Kim, Sangjin Han24 New Types of Queries Queries depending on location of the person asking the query  ‘Give me the best directions to the hospital including the current traffic reports’ Queries depending on direction of movement

Minkyoon Kim, Sangjin Han25 Querying Transient Data Information my change during query evaluation Consider a limited number of paging channels

Minkyoon Kim, Sangjin Han26 Conclusions Identified a number of new research problems arising due to mobility Provided preliminary solutions  Update control problem  Query processing problem