19. A non-transitory computer readable storage medium storing a program of instructions executable by a machine to perform a method of visualizing content change of a data collection over time, comprising: receiving a topic derived from the data collection; extracting a set of documents relevant to the topic from the data collection; segmenting the 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.
19. A non-transitory computer readable storage medium storing a program of instructions executable by a machine to perform a method of visualizing content change of a data collection over time, comprising: receiving a topic derived from the data collection; extracting a set of documents relevant to the topic from the data collection; segmenting the 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. 20. The non-transitory computer readable storage medium of claim 19 , wherein the deriving the set of document clusters comprises performing a constraint-based topic analysis applying constrained clustering algorithm with the generated temporal and visual constraints.