Study On Key Technology In Multidatabase System

With rapid development of internet technology and database technology, more and more application systems have to access many heterogeneous and distributed database. Multidatabase system can provide a uniform and compositive multidatabase environment and make user access these databases by using a uniform schema and a simple query language without changing these databases.The basic task of transaction management is that the concurrency of read-write, guarantee the ACID characteristic property and the database operation correctly. Transaction management mainly uses concurrency and restores mechanism to maintain the characteristic of ACID. Concurrency controls maintain the consistency and the independence.The automicity and durability depend on recovery mechanism.MDBS is built on many of LDBS, these LDBS stored a few data of semanteme relevances. But, these LDBS are developed independently. They have differences in aspect of inquiry language, data pattern and system Structure. For being able to provide consumer with many integrated and unified multidatabase environment, uniting different LDBS data pattern is necessary. This is MDBS to be hit by pattern dispeling of isomerism. It is also called pattern integrated.In MDBS, the overall inquiry which the user submits generally involves the operation dealing with LDBS to many different data patterns. Therefore the overall inquiry must be decomposed into certain overall son inquires. Each son inquiry only carried on one LDBS. LDBS can not distinguish with the overall son inquires which writed by the language of overall inquiry. Therefore the overall son inquires must be transformed into inquiry sentences writed by the inquiry language on LDBS. In order to reduce the response time of the overall inquiry and the implementation price. It needs optimization of the decomposition of inquiries and the result of son inquiries.In this thesis, schema integration, global query decomposition and optimization and global transactions manipulation in multidatabase systems are discoursed elaborately. The algorithm which clears up one to one entity conflict and query process optimization algorithm are presented and analyzed. The assurance strategy of transaction atomity and global deadlock resolution algorithm are also discussed in this thesis. At end of this thesis, a new multidatabase system model is presented by combining multidatabase system and corba technology, and security mechanism is introduced in this model.