The Research And Application Of Query Optimization In Distributed Database System

Distributed database, an important part of database system, is a combination of the technology of database and Internet. People begin to focus on the development of distributed database when traditional database technology and Internet becoming more and more perfect.Query of distributed database is to provide an interface between user and database, which is key technique in this field. Querying in distributed database system is more complicated than in centralized database system. And different ways to query may cause differences in the transmission costs, parallelity and response time. Although some technique and ways to query in centralized database system can also be used in distributed one, there are basic differences between them in terms of scale and factors of databases.There are two different standards to evaluate the results of query optimization in distributed database system. One is to minimize the total costs which include not only CPU, I/O costs but also transmission costs on the Internet. The other is to shorten the querying time. These two stardards are often used at the same time. If necessary, when one is considered as the main standard, the other can be used as secondary standard.The transmission costs on the Internet is considered as the main element of the total costs in the paper. This paper is mainly discussing semi-join technique which is used to reduce the transmission costs in Book-borrowing Management System.