The Research And Design Of Synchronization Model-based In Replicated Mobile Database System

The advancement of mobile database system meets the requirement of data processin mobile computing environment. The replication mobile database system using thedata replication and data synchronization technology is a very important model ofmobile database, which supports the data operations on mobile devices in disconnectionsituations. In such a mobile database model, the key issue is how to replicate andsynchronize the data more efficiently while ensuring the data consistency.Replication is one of the key techniques in promoting the performance of mobiledatabase systems. A lot of researches have been focused on mobile database replicationrecently, and many models and algorithms have been proposed. However, most of thework does not focus on the conflict reconciliation problem. Some approaches that dofocus on the conflict resolution require specialized knowledge of the system for alltransactions and special concurrency control models, which limits their adaptability.Besides, some proposed methods do not ensure transaction serialize ability, which cancause serious consistency problems in many circumstances. In order to solve theseproblems, in the paper, we propose an evolutionary data synchronization mechanismwhich uses union-transaction result set as its granularity of synchronization and a newmobile database replication scheme, Union-Transaction-Level Result-Set Propagation(UTLRSP) model. The conflict detection and resolution strategy of UTLRSP model isdiscussed in detail, and the implementation algorithm is put forward. In UTLRSP model,mobile users are allowed to access local replicas of the database and locally commitmobile transactions when the system is disconnected. The locally committedtransactions are sent to the fixed database server for conflict reconciliation and result-setincorporation when the system is reconnected. In order to ensure database consistency,transactions locally committed at mobile hosts need to be validated at the databaseserver before they can be globally committed. Therefore, union transactions that haveexecuted conflicting operations will be aborted, and only those union transactions thatdo not violate the consistency of the database system can be globally committed.UTLRSP model uses an incremental refresh method, and only recently updated dataneed to be transmitted during the synchronization process. Besides, by utilizing asimplified log structure and by introducing time version and access control into thesystem, UTLRSP model reduces the resource consumption and communication costs.To sum up, through an efficient conflict reconciliation and union transaction result-setpropagation strategy, UTLRSP model provides a flexible and effective solution to thereplication problem of mobile database systems. Finally, we take advantage of typicalthree-level architecture of mobile database solution to implement our system, anddescribe the key technologies which are used in client application (including embeddeddatabase management system), synchronization server and center database server inmore details. In the last section of this thesis, we analyze the performance of this synchronizationmethod and UTLRSP model, comparing them with some other methods and models inseveral different aspects. A basic conclusion is given as the end of the thesis.