In order to improve the two-level signature file method designed by Sacks-Davis et al.[20], we propose new multikey access methods based on term discrimination and signature clustering. By term discrimination, we create separate, efficient access methods for the terms frequently used in user queries. We in addition cluster similar signatures by means of these terms so that we may achieve good performance on retrieval. Meanwhile we provide the spacetime analysis of the proposed methods and compare them with the two-level signature file method. We show that the proposed methods achieve 15-30% savings in retrieval time and require 3-9 % more storage overhead.