1. Mobile Databases: a Selection of Open Issues and Research Directions Authors: Rachid Guerraoui et al. Sources: SIGMOD Record, 33(2), pp.78-83, 2004 Adviser: Min-Shiang Hwang Speaker: Chun-Ta Li

2. Outline Introduction Data Synchronization Mobile Transactions Embedded Databases Data Privacy and Confidentiality P2P Dissemination Models Middleware Adaptability Conclusion Comments

3. Introduction Mobile Client – Fixed Host –Data Service Provider (banking data, agenda) –Servers broadcasting information (traffic, weather) Requirements –Data consistency (disconnected computing) –Data confidentiality –Data availability (new data access model)

4. Introduction (cont.) Mobile Client – Mobile Host –Portable folders (medical folder on a smart card, phonebook on a SIM card) Requirements –Database embedded in ultra-light devices –Data durability (replica – fixed network – crash resiliency) –Copy synchronization – collaborative applications –Query execution

5. Introduction (cont.) Fixed Client – Fixed Host –Moving objects –Authors do not cover this issue Hardware/Software constraints –Low bandwidth of wireless communication –Frequent disconnection –Scarce computing

6. Data Synchronization Disconnected work (merging divergent data) Three properties for synchronizing data –Causality preservation –Intention preservation –Convergence Every operation is processed in four steps –Generated at one site –Broadcasted to the other sites –Received by them –Executed remotely on them

7. Data Synchronization (cont.) Operational Transformation Model –Integration algorithm Receiving, broadcasting and executing operations –Transformation function Merging two concurrent operations defined on the same state Two research directions –Transformation model – short/longer disconnection –Minimize the size of the log (compression)

8. Mobile Transactions Transaction – mobile unit (MU) Disconnection – global commit –Unilateral commit –Time-out based Transactions at MU are grouped into long- duration transactions (LDT) –Local environment is initialized at the MU in connected mode –LDT are performed at the MU, possibly in disconnected mode and are locally committed –LDT are globally committed when the MU gets a stable connection with the fixed server

9. Mobile Transactions (cont.) To associate each LDT with a contract Main issue to the notion of contract –How to specify them –How to derive operational rules to maintain them at execution time –How to use them to facilitate the reintegration of locally modified copies with the server copies in order to increase the global commit rate

10. Embedded Databases Database techniques embedded in lightweight computing device – hardware constrained New important research efforts have to be undertaken –Capture the impact of each device hardware constraint on databases techniques –Propose new storage, indexing and query techniques –Set up co-design rules to help calibrating the hardware resources of future device

11. Data Privacy and Confidentiality Traditional data bases security principles –User authentication, communication encryption, server enforced access control et al. –Inoperative against insider attacks Server-based security approaches Client-based security approaches

12. Data Privacy and Confidentiality (cont.) C-SDA (Chip-Secured Data Access) –Client-based security component –Between client and an encrypted data –Embedded into a smart card to prevent any tampering to occur on the client side Requirements –More complex data (semi-structured data) –Push-based model (selective information broadcasting) –Sophisticated access right models (rules, permission, prohibition, obligation)

13. P2P Dissemination Models Traditional central database server –Failure and a performance bottleneck –Scalability Decentralize the database maintenance Questions –How do processes get to know each other, and how many do they need to know (membership maintenance) –How to make the connection between processes reflect the actual network topology –Which information to drop at a process when its storage buffer is full (buffer management) –Message filtering

14. Middleware Adaptability The adaptation at various levels –Applications, Middleware, System resources –From any place and any terminal type Research directions –Compatibility with standards (framework) –The middleware layer (reflection or self-adaptability properties) –The concept of fidelity (multi-dimensional) Temporal consistency, semantic consistency, security level, or data precision

15. Conclusion Strong hardware/software constrain Defined a number of research directions Performance, scale-up, quality, adaptability

16. Comments User aspects –Human friendly –Costs/Practicability Technical aspects –Performance (time/space) –Standard Applications