1. A method of visualizing content change of a data collection over time, comprising: receiving one or more topics derived from the data collection; extracting a set of documents relevant to each topic from the data collection; segmenting each topic into multiple non-overlapping temporal segments, the segmenting comprising: generating temporal and visual constraints; deriving from the set of documents a set of document clusters that satisfy the temporal and visual constraints, a document cluster in the set of document clusters identified with a sub-topic; and determining a temporal segment boundary associated with said document cluster, wherein the temporal segment boundary identifies a temporal segment for the sub-topic; selecting a set of representative keywords from the document cluster to summarize the temporal segment; and generating a time-based, interactive visual summary of the data collection.