15. A method according to claim 11 , further comprising: generating one such spine group, comprising: arranging two or more clusters of documents along a spine based on concepts of the clusters; and grafting at least one other spine of clusters to one of the clusters arranged along the spine.
15. A method according to claim 11 , further comprising: generating one such spine group, comprising: arranging two or more clusters of documents along a spine based on concepts of the clusters; and grafting at least one other spine of clusters to one of the clusters arranged along the spine. 17. A method according to claim 15 , wherein the cluster on which the other spine of clusters is grafted is most similar to the other spine of clusters.