Research On Key Technologies Of Mobile Database Systems

Advances in computer and telecommunication technologies have made mobile computing a reality. In mobile computing environment, users can access information through wireless connections regardless of their physical location. In the last decade, this new kind of computing paradigm has gained great development and posed new challenges to database researchers. In mobile database systems, new features such as mobility, disconnection, low bandwidth, high bandwidth variability, heterogeneous networks and security risks make traditional database processing schemes no longer well suited. Therefore, it is necessary to develop new models and algorithms to deal with this new situation.This thesis explores the key technologies in mobile database systems from two aspects. (1) How to eliminate the unfavorable impact on information access posed by mobile computing environment. In this aspect, my research is mainly focused on mobile database replication and mobile transaction processing. (2) How to take advantage of the desirable features introduced by mobile computing and to provide location-based services. In this aspect, my research concentration is on moving objects databases and location dependent data processing.Replication is one of the key technologies in promoting the performance of mobile database systems. In this thesis, a novel mobile database replication scheme, Transaction-Level Result-Set Propagation (TLRSP) model, is put forward. The conflict detection and resolution strategy based on TLRSP is discussed in detail, and the implementation algorithm is proposed. In addition, a new synchronization scheme, Double-Timestamp Transaction-Level Synchronization (DTSTLS) model is put forward to solve the synchronization problem under the 3-tier replication architecture (Mobile Client - Synchronization Server - Database Server). DTSTLS utilizes a novel double-timestamp strategy to promote the efficiency of synchronization. Besides, it ensures serializability and consistency of the mobile database system through transaction-level conflict reconciliation.Mobile transaction processing is another key technology to provide efficient information service in mobile computing environment. In this thesis, a new mobile transaction model, Optimistic Two-Phase Commit for Mobile Transactions (O2PC-MT), is proposed. O2PC-MT combines Optimistic Concurrency Control and Two-Phase Locking in mobile transaction processing, and utilizes Two-Phase Commit protocol for the global commitment of mobile transactions. In this way, O2PC-MT provides an effective support for the long-lived transaction property. In addition, mobile computers are allowed to submit mobile transactions in multiple request messages and to move arbitrarily during transaction execution. Therefore, O2PC-MT presents a flexible support for interactivity and arbitrary mobility.Moving Objects Database (MOD) technology is very valuable in presenting location...