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Data Access Models in Location Dependent Information Services

Data Access Models in Location Dependent Information Services. Yu Meng May 1, 2004. Outline. Introduction Related concepts Location models Query types Valid scopes Access models On-demand Access Broadcasting Summary. Introduction. What is LDIS What are the challenges

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Data Access Models in Location Dependent Information Services

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  1. Data Access Models in Location Dependent Information Services Yu Meng May 1, 2004

  2. Outline • Introduction • Related concepts • Location models • Query types • Valid scopes • Access models • On-demand Access • Broadcasting • Summary

  3. Introduction • What is LDIS • What are the challenges • Cellular Architecture for LDIS

  4. Introduction • Provide local or nonlocal news, weather, traffic reports, navigation maps and directory services in wireless environment.

  5. Introducton • Mobile environment constraints, • Spatial data, • User movement.

  6. Introduction

  7. Related Concepts • Location Models • Query types • Valid scope

  8. Related Concepts -Location Models • Geometric model. • Latitude-longitude pair returned by GPS. • Advantage: good for heterogeneous system, • Disadvantage: costly in terms of data volume • Symbolic model. • Real-world entities. • Logical entities • Advantage: easy to manage data with well organized structures. • Disadvantage: hard to convert among heterogeneous systems.(good topic for RFC)

  9. Related Concepts -Query types • Local vs. non-local queries. • “Tell the local weather”, • “Find the weather in New York City”. • Simple vs. general queries. • “Download the local traffic report”, • “List the hotels within 30 miles”, • “List the hotels with a room rate below $100”.

  10. Related Concepts -Valid Scope • The area or areas within which the query result is valid. • Data object returned: (query, result, vs) • (nearest-hotel, A, vs), • (nearby-restaurant, {A,B}, {1,2}).

  11. Related Concepts –Valid Scope Example

  12. Data Access Models • On-demand access • Broadcasting • Hybrid of the two.

  13. On-demand Access • Data placement, • Data replication, • Query scheduling, • Indexing.

  14. On-demand Access-Data Placement

  15. On-demand Access-Data replication • The system creates certain copies of the data and places them at different locations in the network. • Work done are based on network topology and access patterns. • Problem: Access patterns may be time dependent periodically or temporally. Is EMM a solution?

  16. On-demand Access-Query scheduling • Query scheduling determines query processing order. • Work has been seen in improving average queuing delay. • What happens if client moves? • Is prediction a solution?

  17. On-demand Access-Query Scheduling

  18. On-demand Access-Indexing • Disk indexing • Geometric location model: MBR based indexing. May be inefficient caused by overlapping. • Symbolic location model: mapping to valid data object is needed. • Several R tree based algorithms are proposed but none works superior to others in all cases.

  19. On-demand Access-Indexing

  20. On-demand Access-Indexing

  21. On-demand Access-Indexing

  22. Broadcast • Broadcast lets an arbitrary number of users simultaneously access data. • Good for simple queries. • Hard for general queries.

  23. Broadcast-Air indexing • Client can download a indexing info to predict availability of queried data. • Indexing size and latency. • Broadcasting strategy: how to divide bandwidth? Based on the statistics. • Not adaptive!

  24. Data Caching • Data may be cached at the mobile clients for better performance. • Data consistency: • Location dependent cache invalidation. • Time dependent cache invalidation.

  25. Data Caching-Data Replacement • LRU • P/X • Distance based algorithm • Valid scope

  26. Data Caching-Data Prefetching • Feasible for simple queries. • May be hard for general queries. • Not much work on this issue.

  27. Summary • LDIS is a developing technology. • Many research opportunities remains. • SPOT (Smart Personal Objects Technology ) announced by Microsoft in 2003

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