1. A system for generating cluster spines, comprising: clusters of documents, each document associated with a document concept formed from one or more terms extracted from that document; a cluster concept determination module to determine at least one cluster concept for each cluster, comprising: a concept ranking module to rank the document concepts; and a concept selection module to select at least one of the document concepts that is highly ranked as the cluster concept; a spine generation module to form one or more spines each comprising two or more clusters that share at least one of the cluster concepts, wherein the shared cluster concept is identified as a spine concept; a cluster assignment module to assign one or more of the remaining clusters to the spines based on a similarity between the cluster concepts for the remaining clusters and the spine concepts for the formed spines; and a processor to execute the modules.