Research And Realization Of The Distributed Medical Image Database System

With the rapid advancement of computer technology, the burden of server has been the bottleneck of network in centralized database system. Distributed database system can not only solve this problem but also improve the reliability of system. Distributed database system is a collection of multiple logically interrelated databases distributed over a computer network. A distributed database system which is based on existed centralized medical image database system is designed. As top-down design process, the system structure is devised newly. Data is fragmented and distributed according to application analysis. Most of queries are restricted to local server, so the burden of network is eased. Although one server in the system is in trouble, others will still work well. The method of distributed query optimization is analyzed deeply which use semi-join algorithm and query tree disassembling. A case is used to prove that the data is transmitted through network will be highly reduced by this way.Data dictionary and distributed view are designed, which can help to make the distribution transparent to the users. The module of distributed query and update is designed to realize the access to database. 2PC protocol is used to assure distributed transaction rollbacks when error is occurred. With data replication technology, any change in one server will result in the change in other servers. A module of managing users' grants is approach to realize the safety of database. With this method, users' grants can be managed over whole distributed system.