Asymmetric Visual Hierarchy Comparison with Nested Icicle Plots

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Package structure of the Azureus project as primary hierarchy in comparison to a clustered decomposition as secondary hierarchy

The comparison of hierarchies is a data analysis task for that a number of visualization approaches already exist. Generally, this can be regarded as a special form of graph comparison. These techniques typically handle two or more compared hierarchies all in the same way. In many practical applications, however, there are reasons why one of the hierarchies is more important than others. We, hence, propose a novel visualization approach to reflect this asymmetry in importance. A focused primary hierarchy is visualized as a large icicle plot, whereas a secondary hierarchy is only shown on demand, nested in the nodes of the primary hierarchy. Similarities of the two hierarchies are color-coded. We show the applicability of the approach in a case study comparing a hierarchically organized software system to a clustering result.