A method for using dual indices to support query expansion, relevance/non-relevance models, blind/relevance feedback and an intelligent search interface, comprising using a computing device to: access 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 determine a number of “N” IUs in the results that are regarded by the computing device to be relevant by accessing a forward index; and use the forward index to perform any one from the group consisting of: computing query expansion weights for top “N” retrieved IUs, building the relevance models by the contexts of query terms in the top “N” retrieved IUs, and finding the longest contiguous sequences of query terms in a query found in an IU; 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.