System and method for displaying a threaded document

A threaded document display system generates a virtual document by combining documents within a thread, enabling easy understanding of relations between threaded documents and providing the ability to view multiple documents in a required collection simultaneously. A relation between threaded documents is extracted as a tree structure. A section group with this tree structure is generated in a virtual document from the extracted tree structure before mapping a relation between the documents. Contents of documents corresponding to respective sections are mapped and displayed. Consequently, a plurality of documents may be mapped into a single virtual document. The display shows the content of the virtual combined document rather than a document list. Even if a section is treated as an object embedded in a higher sentence, such as a nested structure, relations between independent documents may be mapped into a single document without expanding a text of the higher document.