4. A system for generating a reference set for use during document review, comprising: a collection of unclassified documents; a clustering module to identify one or more features within each of the unclassified documents, to generate clusters of the features, and to select at least one feature from one or more of the clusters as reference set candidates; a classification module to assign a classification code to each reference set candidate; an identification module to refine the reference set candidates by grouping the reference set candidates into further clusters, selecting at least one of the reference set candidates in one or more of the further clusters, and assigning a classification code to the further reference set candidates; a data module to form a reference set from the unclassified documents associated with the further classified reference set candidates; and a processor to execute the modules.
4. A system for generating a reference set for use during document review, comprising: a collection of unclassified documents; a clustering module to identify one or more features within each of the unclassified documents, to generate clusters of the features, and to select at least one feature from one or more of the clusters as reference set candidates; a classification module to assign a classification code to each reference set candidate; an identification module to refine the reference set candidates by grouping the reference set candidates into further clusters, selecting at least one of the reference set candidates in one or more of the further clusters, and assigning a classification code to the further reference set candidates; a data module to form a reference set from the unclassified documents associated with the further classified reference set candidates; and a processor to execute the modules. 6. A system according to claim 4 , further comprising: building a hierarchical tree of the clusters; and traversing the hierarchical tree to identify the reference set candidates.