Developement and Implementation of Access Protocols for Heterogeneous Distributed Database Systems

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The aim of this research was to investigate the feasibility of heterogeneous federated distributed databases, especially focusing on its application for the document delivary on high-speed wide area networks, such as digital libraries on the Internet.The first step we have done is a theoretical analysis of the distributed database query processing. In a distributed database with similarities in their schemata, it is required to introduce a query decomposition method for sending sub-queries to each database servers whose database are relevant to the issued query. We studied the decomposition method of queries, introducing the concept of 'virtual database' and 'component database'. The presented method of schema integration allows us to issue a database query without considering logical distribution of component databases, using an algorithm for automatically decomposing the query and transmitting sub-queries to several relevant servers.Along with the decomposition algorithm and query processing method, a theory for the correctness and soundness of the proposed methods is also developed based on the relational theory.The presented method can generally provide us a large set of query results than the set given by the conventional methods which issue queries separately to each server. The investigators also showed that the degree of increase of the result set by simulation.The presented algorithm was implemented on a prototype database system which holds sample bibliographic information. The system, which is operational on a local area network, demonstrated the effectiveness of the presented method by giving larger number of resultant records for example queries.This investigation could reveal fundamental methods and implementation strategy by theoretical analysis of queries over heterogeneous distributed database environment, and it will be effective on wide-area networks such as the Internet.