A system for constructing, in a storage device of a computer, data expressing a document to be revised as an XML document, in which a volume, a chapter, a clause, an item, a section, a sub-section, a paragraph and the like of the document to be revised are expressed as a tree structure is provided. An element corresponding to a branch node of tree structured data is assigned a set of a unique revision ID and an attribute representing a type of the revisions written in a list structure every time a revision is made and the element prior to the revision is saved so that a revision operation of the element is performed using the information.