Abstract: Convenience of a user is improved in handling data included in a plurality of structured document files. A child document file is created by a schema inheriting a schema in a parent document file in which a plurality of tags are structured. A name of a substance tag in a child document file inheriting a model tag included in a parent document file is changeable in accordance with a user's input direction. At the time, a tag mapping table is held, in which a name of a substance tag included in a child document file and a name of a model tag which is the origin of the substance tag are associated with each other. A name of a substance tag corresponding to a model tag of which name is a search key is detected, with reference to the tag mapping table, and then, the data of the substance tag is detected from the child document file, by using the name of the substance tag as a new search key.