17. A system for retrieving documents from a database comprising: a graphical user interface which enables a user to select text fragments of a displayed text string of one of the documents in the database, the one of the documents being retrieved in response to a user query, the displayed string being labeled with tags corresponding to grammar rules associated with the text fragments of the displayed text string, the grammar rules being selected from a plurality of rules, the graphical user interface configured for displaying the labeled grammar rules of the text fragments of the displayed text string enabling a user to select fewer than all of the grammar rules associated with the text string, the processor applying the grammar rules selected by the user to retrieve additional text strings from the database which satisfy the user-selected grammar rules; and a processor which identifies the grammar rules associated with the selected text fragments and generates a new query for retrieving documents that comprise a text string which satisfies the grammar rules.
18. The system of claim 17 , wherein the graphical user interface is configured for displaying grammar rules associated with user-selected text fragments, whereby a user selects those grammar rules which express a query.