| Date integration is an important direction in the filed of database research. With the growing importance of XML as a data exchange and storage format, researchers gradually shift their focus to XML-based data integration, and intensive interests have been triggered on the issue how to manage and retrieve XML information efficiently in XML-based data integration systems. Under such circumstances, the dissertation explores the issues of data replication and query processing in XML-based data integration system. The key contributions are the followings.1. The dissertation investigates the issue how to optimize XML queries using the schema information, and presents an algorithm on path expansion to lower the processing overhead of non-deterministic regular path expression in ordered XML queries,2. An effective approach to improve the performance of data integration systems is to discover frequent XML query patterns and replicate frequently accessed attributes or documents. The dissertation presents several efficient algorithms to discover frequently occurred ordered XML query patterns or unordered XML query patterns respectively. Experiments show that our algorithms result in significant performance gains.3. The dissertation proposes an algorithm to discover frequent XML query patterns incrementally, and presents a method to choose dynamically the intervals at which the incremental mining algorithm should be re-run.4. The dissertation gives a necessary and sufficient condition of self-maintainability of materialized XML views, and presents an algorithm to implement self-maintenance of XML views to preserve the consistency of replicated data with data sources when base data changes.
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