1. Mobile Databases J. H. Wang May 2011

2. Outline Overview Issues in Mobile Databases –Data management –Transaction management Mobile Databases and Information Retrieval Future Challenges and Issues

3. Mobile Database Systems Distributed system with mobile connectivity Full database system capability Complete spatial mobility Wired and wireless communication capability

4. Possible Applications Traffic control Taxi dispatch Emergencies services: police, medical, fire, … Car navigation Location-aware search and recommendation Social applications: information / opinion sharing and search among community …

5. An Example Application: Taxi Dispatch [Source: Alibaba.com]

6. Possible Limitations Limited wireless bandwidth and communication speed Limited power (battery life) Limited screen size for output Limited query capability for input Limited computing & storage capacity Less secure

7. Capabilities Anywhere: can physically move around without affecting data availability Anytime: can store and retrieve any data whenever mobile connection is available Efficiency: can process mobile data efficiently Effectiveness: can give users what they really want (, and skip the less relevant…)

8. Goal To build a ubiquitous information processing system given the inherent limitations of mobile devices and wireless communications

9. Architecture of a Typical Mobile Platform Wired Internet BS Mobile node Base station Wireless domain Fixed node

10. Architecture of Mobile Database Systems Database Internet server client BS

11. Issues in Mobile Databases Data management –Data caching –Representation and storage of mobile data –Data classification Transaction management –Mobile query processing –Mobile concurrency control –Transaction and error recovery

12. Data Management Issues How to improve data availability to user queries in mobile database systems? –Data caching Results of previous queries are cached on mobile clients Query log can be further used in personalization and recommendation –Representation and storage of mobile data Spatial data management Indexing and retrieval schemes –Data classification Location-dependent Location-independent

13. Data Caching Results of previous queries are cached on mobile clients –Cache size –Cache freshness/update frequency –Cache consistency Query log can be further used in personalization and recommendation –User preference learning keywords, categories, location –Collaborative filtering for content recommendation

14. Representation and storage of mobile data Spatial data management –Location information –Data volume, update frequency, persistency Indexing and retrieval schemes –High-dimensional feature space –Structure for improving retrieval efficiency

15. Data classification Location-dependent –Location-based services E.g. nearby gas stations or restaurants within 1km, available paths to the park, … –Database distribution or replication must take location into consideration Distributed vs. centralized Location-independent –Personal name, account information, plate number, …

16. An Example Location-based Service [Source: Google Maps Realtime Traffic]

17. Transaction Management Issues Mobile query processing Concurrency control Transaction and error recovery

18. Mobile Query Processing Query types –Location dependent query –Location aware query –Location independent query Query constraints –Query response time –Search-result accuracy –Throughput: number of queries per time unit

19. Location dependent query A query whose result depends on the geographical location of the query origin –E.g. What are the 3 nearest gas stations or restaurants? What is the shortest path to the park? –GPS can facilitate this Outdoor only WLAN could cover most of the indoor locality

20. Example Find the nearest gas stations –[Source: Google Image Search]

21. Location aware query A query whose context might be related to locations –E.g. Find out all the car plates passing through the traffic light between 7:00-8:00pm Find out the current location of the bus on route #212 Find out the top 5 road segments that have the most traffic in Taipei (the slowest car speed)

22. An Example Red light cameras –[Source: St. Petersburg Times]

23. Query constraints Query response time –Realtime query Search-result accuracy –Distance, time, path, traffic flow, … Throughput: number of queries per time unit –Scalability: large number of simultaneous queries

24. Mobile concurrency control Similar to the issues of concurrency control in distributed systems –Time synchronization Timestamps, clocks –Latency in mobile queries –Similar issues to cache consistency Size of query results

25. Transaction and error recovery Conventional transaction properties –Atomicity –Consistency –Isolation –Durability Too rigid for mobile database –Flexibility can be introduced

26. Possible issues in mobile transactions Transactions –Wireless communication availability and overhead –Hard to manage locking and unlocking operations –Limited power Recovery –Efficient logging and checkpointing –Log duplication

27. Other Concerns In mobile e-commerce, security in mobile data and transactions are critical –Less support in wireless security WEP, IEEE 802.11i –Identity authentication –Privacy issues of user location

28. Mobile Databases and Information Retrieval Mobile information retrieval –Context awareness –Content adaptation Existing mobile search services –Mobile Web browsing –Text messaging (SMS)

29. Context Awareness Location information Built-in camera Social networks

30. Possible research topics related to context awareness Location-based search Spatial data mining Query log mining User profiling and recommendation Knowledge sharing

31. Content Adaptation Small screens Less processing power Less memory and storage

32. Possible research topics related to content adaptation Automatic summarization Information filtering User personalization Efficient indexing and retrieval of mobile media Effective structure for mobile data storage Scalable algorithms

33. Common Types of Mobile Web Services Mobile Web browsing –Search: Web pages, images, products, local, movies, … Text messaging –SMS Others –Maps –GPS

34. Existing Mobile Search Services Google –Google Mobile –Google SMS –Google Maps for Mobile Yahoo –Yahoo! Mobile –Yahoo! Go Others –AOL, MSN, 4INFO, …

35. Google Mobile (1/2) http://mobile.google.com/ (XHTML) (WML)

36. Google Mobile (2/2) (Images)(Mobile Web)

37. Google SMS http://www.google.com/sms/

38. Google Maps for Mobile http://www.google.com/gmm/

39. Future Challenges and Issues Indexing and storage of mobile data Efficient query processing and retrieval of mobile data Content adaptation and information presentation for small display User interface design for mobile search Automatic summarization and personalization of mobile data Scalable algorithms for large mobile databases Knowledge sharing among mobile peers Security and trusted retrieval of mobile data Location-based search for mobile devices

40. Other Resources Recent academic events –Workshop on mobile information retrieval (MobIR 2008), in conjunction with SIGIR 2008 –International workshop on mobile information retrieval for future (MIRF 2010) –International workshop on mobile and ubiquitous information access (MUIA 2009), in conjunction with ECIR 2009 –International workshop on mobile multimedia information retrieval (MoMIR 2009), in conjunction with MoMM 2009

41. Other Related Fields Mobile Ad Hoc Network (MANET) Mobile Peer-to-Peer Network (P2P) Ubiquitous Computing or Pervasive Computing

42. Thanks for Your Attention! Further reading: –Vijay Kumar, Mobile Database Systems, Wiley- Interscience, 2006. –F.S.Tsai, M. Etoh, X. Xie, W.C.Lee, and Q. Yang, Introduction to Mobile Information Retrieval, IEEE Intelligent Systems, Vol. 25, No.1, pp.11-15. –Communications of the ACM, Vol.48, No.3, The Disappearing Computer, Mar. 2005. –Communications of the ACM, Vol.45, No.12, Issues and Challenges in Ubiquitous Computing, Dec. 2002.