A method for using dual indices to support query expansion, relevance/non-relevance models, blind/relevance feedback and an intelligent search interface, the method comprising: accessing an inverted index to obtain an initial retrieval of results in response to a query, and to generate a rank list of the results, the results referring to information units (IUs) where the query occurs; and determining a number of “N” IUs in the results that are assumed to be relevant by accessing a forward index; wherein the forward index and inverted index have pointers to locations in the IUs where terms of the query occur, and the forward index retrieves a term frequency vector of the IU or a set of contexts of the IU.