Efficient Query Processing in Integrated Multiple Object Databases with Maybe Result Certification
IEEE Transactions on Knowledge and Data Engineering
The intrinsic problems of structural heterogeneity and an approach to their solution
The VLDB Journal — The International Journal on Very Large Data Bases
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In a multidatabase system which consists of object databases, a global schema created by integrating schemes of the component databases provides a uniform interface and high level location transparency for the users to retrieve data. The mapping information between the global and component schemas is important for the global query processing. In this paper, a mapping strategy is presented. A mapping equation is defined to denote the mappings for attributes and object instances among a virtual class and its constituent classes. In addition, a mapping graph is used to describe the mapping equation. According to the mapping information, the mechanism to process global queries is introduced. One processing unit is responsible to decompose the global query into the subqueries against the component databases. Moreover, to handle the effects of schema restructuring, preprocessing and postprocessing units are provided for each local DBMS. Finally, the results returned from component databases need to be integrated. The certain result and maybe result for a global query are discussed. Also, the situation where a real-world entity is represented in different component databases as different objects is considered for the result integration.