1. A computer-implemented method of querying an index of first objects comprised of a plurality of index entries and a pool of second objects, the method comprising: evaluating the index of the first objects to produce a group of one or more possible candidates based on whether one or more index entries of the first objects satisfy a query; adding second objects from the pool to said group of possible candidates to produce an interim group of possible candidates: filtering the interim group of possible candidates by comparing approximations of the candidates of the interim group with the query to produce filtered candidate objects; and determining if the filtered candidate objects satisfy the query by comparing the first and second objects corresponding to the filtered candidate objects with the query.