Abstract: Upon receiving XML data input, a database management system calculates a processing cost for reflecting the XML data to an index. If the calculated processing cost exceeds a predetermined threshold, the database management system stores structure analysis information concerning the XML data in a structure analysis information storage area. When an input of a retrieval request of the structured data containing a structure condition of the structured data is accepted and structured data that is an object of the retrieval request is structured data that is not reflected to the index, the database management system takes out structure analysis information stored in the structure analysis information storage area, discriminates a range of XML data that becomes the object of the retrieval request, and conducts retrieval over the range.