Study And Implementation Of Web Distributed Database System

~I3 S Th~c~T? Information might be stored in heterogeneous location-distributed databases in distributed database system environments. How to select and renew data distributed in distributed database system in global logic is problems which distributed database technologies mainly solve, distributed database technologies are combined with database technologies and computer network technologies. Besides the characters of central database, it has its own specialities:It not only thinks of the autonomy of local node,but focuses on solving the logical integrity of global database; Except that it possesses logical independency and physical independency that central database has,it has data distribution independency that includes three layers of meanings which, from the top to the bottom,in turn are :slicing transparency allocation transparency data type transparency on local node . In addition, in query conduct ?. transaction management concurrence control . data integrity and security and so on , distributed database system has more complex and richer content. The dissertation simply introduces some knowledge of central database at first, then mainly introduces some knowledge of distributed database including the system structure of distributed database system data slicing and data allocation ... distributed query conduct .. distributed transaction management distributed concurrence control .. distributed database integrity and security and distributed database system development, At last give a tangible application example of distributed database system. The example is that each sub-company in a general company transfer the data in its own database into the database server of the general company so that the general manager anaiyses and ~III~v~ evalutes the prodctiofl and management of each sub-company through which the manager makes general decisions. To realize this target , databases of each sub-company and the general company are indispensible, in addition, data must be transferred between each sub-company and the general company through the local area network or wide area network. Data transfer is realized by PowerBuilder?Pipeline. In application programme, also give tangible realization of security of the distributed system and the management of distributed data and the transparent query of distributed data. The management of distributed data incarnates local data抯 independence global data抯 integrity and the relation of local data and global data through data transfer. Through the security protocol, the security of data transfer can be ensured.ApplicatiOfl systems similar to the application system usually adopt two layer structure of clientlserver.The application system adopt three layer structure,which extends application scope of the application system. .On every sub-company node, not only transfer data into the database of the general company ,but also among sub-company node realize the transparent query of distributed data . In this implication system, the transparent query of distributed data on every sub-company node all regards the general company node as implication server. The real realization of the transparent query of distributed r...