For those of you into IR he discusses the use of set oriented faceted search to refine the meaning of a users query, particularly with the goal of involving the

For those of you into IR he discusses the use of set oriented faceted search to refine the meaning of a users query, particularly with the goal of involving the user in the refinement. He finds a set oriented approach to be better than clustering, which tends to be opaque. The discossion of faceted search begins around minute 29.