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This paper describes general storage and retrieval methods for XML documents using object-relational databases. The storage method decomposes tree structure of XML documents into nodes, and stores them in relational tables according to the node types. By using this method, being independent of DTDs or element types, any XML documents can be stored in databases. Also it is possible to utilize index structures(e.g. B ⁺ trees, R trees, etc.) which are provided in database management systems. As for retrieval, we show the transformation of XQL queries into SQL queries. It is possible to realize the storage method by doing minimal extension to object-relational databases and the retrieval method by adding a preprocessor of a query language.We also performed experiments using XML documents on the plays of Shakespeare, to show the effectiveness of our methods.