The database integration reference apparatus stores therein metadata for integration which defines the structure of the XML file used for outputting the query result, the correspondence relationship between the elements in the XML file and the elements in the databases, and the correspondence relationship among the elements in different databases. Using the metadata for integration, pieces of data that are distributed in a plurality of databases including an XML-DB and an RDB are integrated so that the user recognizes the distributed data as one virtual XML file. A query that is made to the integrated data and is written in an XML query language called XQuery is received, and a piece of integrated data is extracted in an XML format and output to the user terminal.