嵌入式移动实时数据库中一种基于代价模型的查询优化技术

AbstractWith the cutting edge technology advance in wireless and mobile computers,the queryprocessing in a mobile environment involves join processing among different sites whichinclude static servers and mobile computers.Because of the need for energy saving and alsothe presence of asymmetric features in a mobile computing environment,the conventionalquery processing for a distributed database cannot be directly applied to a mobile computingsystem.the regular optimization algorithms of distributed query,such as the optimizationalgorithm based on join,the optimization algorithm based on semi join,SDD-1 algorithm,have been greatly researched and widly used in DDBMS.Mobile DBMS is one kind ofDDBMS which supports mobile computing.However,the regular optimization algorithmsused in DDBMS must be developed so as to apple to the Mobile DBMS.without doing anychanges,these algorithms won't be fitted for the mobile computing environment.There are many asymmetric features in a mobile environment.Then,in light of thesefeatures,query processing methods for both join and query processing can be devised.Intuitively,employing semijoin operations in a mobile computing environment is able tofurther reduce both the amount of data transmission and energy consumption.According tothose asymmetric features of a mobile computing system,two different join methods havebeen examined.For query processing,which refers to the processing of multijoin queries,two query processing schemes are devised.It is shown by the simulation results that,by exploiting the asymmetric features,thesecharacteristic functions are very powerful in reducing both the amounts of energyconsumption and data transmission incurred and can lead to the design of an efficient andeffective query processing procedure for a mobile computing environment.Key words:mobile computing,query processing,join method,multijoin queries.