Visualizing hierarchy changes by dynamic indented plots

Visualizing static hierarchical organizations has been a focus of information visualization for many years, but it still remains challenging to produce visual representations of evolving, i.e. dynamic hierarchies. In this paper we extend the concept of indented plots to also support the depiction of changing hierarchies. We exploit the concept of static diagrams in order to support the preservation of a viewer´s mental map. Changes between subsequent hierarchies are precomputed and visually indicated by color coded straight or curved lines depending on the type of change. Interactive features can be used to aggregate or collapse the dynamic hierarchy data in the supported dimensions, i.e. the vertex as well as the time dimension on different levels of hierarchical and temporal granularity. The usefulness of our technique is illustrated by means of a bibliography dataset where we show the changes in the yearly prefix tree acquired by extracting words occuring most frequently in more than 2,000,000 paper titles from the digital library DBLP.