1. A method for presenting related information in a document processing system which includes an input device, a display device, a processor and a document storage, the method comprising the steps of: a) inputting a word string through the input device; b) extracting a related element from the word string, the related element comprising two words and a relational word which indicates a relation between the two words; c) retrieving a related word string from the document storage, the related word string including the related element; and d) presenting the related word string to a user through the display device.