Study And Realization Of Mobile Database System-Mobile NHDB

NHDB is DBMS developed by our group. Users can access the'database'through a subset of SQL. We implement a prototype of mobile-database system based on NHDB.Mobile NHDB simulates the transmission of mobile communication system on local network. We can simulate almost all the characteristics of mobile communication, such as instability of mobile connections and the moving of mobile terminal by calling the relative interfaces.The data replication model is the most important model among the mobile database system. We analyze the previous replication algorithms, and bring forward a new replication algorithm on the basis of'access rate'. Different from the previous which account the access of data items, the algorithm records the relative access rate of attributes. In the way, a large amount of memory space and CPU time is saved. And the structure of restoration in the bottom level is adjusted, which greatly benefits to the restoration of data and replication process.Referring the multi-channel data broadcast and the index mechanism of single broadcast, we improve the data broadcast algorithm and put forward an adaptive multi-channel data broadcast algorithm. And we also bring forward the strategy of optimizing the transaction and data broadcast process.At the end of this dissertation, the interface of Mobile NHDB is represented and the combination of mobile database and Agent is introduced represent. We also summarize the limitations of Mobile NHDB and give out the new approaches and directions of further research.