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Interactive Visualization of Hierarchical, Multi-Variate, and Time-Varying Data

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Hierarchical data sets – e.g. software system structure data – are collected on a growing scale. In order to understand a software system, the data sets are visualized and analyzed. As software changes frequently, the analysis of data sets at different points in time is important for the comprehension of their evolution. Existing approaches for the visualization of temporal hierarchical data have their limitations either in the amount of visualizable data or in the comparability of data sets at different points in time. The visualization of hierarchical structures in complex software systems is usually done using a treemap. A treemap recursively subdivides a two-dimensional area in order to encode a hierarchy and enables the visualization of multiple attributes e.g. with the size, the extruded height or the color of a node. Traditional treemap layout algorithms and rendering techniques can only be used for the comparison of two data sets at different points in time to some extent, as (1) no comparison between nodes in a treemap and between different states is possible and (2) there are no rendering techniques for the size differences of a node over time. This thesis introduces the techniques EvoCell-Layouting, Change Map, and Change Hints. EvoCell-Layouting is a novel treemap layout algorithm that iteratively changes a given treemap layout. Change Maps are density maps to locate changes in attribute values disregarding the difference and the size of the node. Change Hints visualize spatial changes between two states of a treemap. These three techniques enhance the comprehension of the evolution of temporal hierarchical data. A prototypical implementation, a discussion about alternatives, and performance and memory analyses demonstrate real data applicability. An additional case study reveals distinctive changes in the software system of a monitored open-source project that are hard to detect with traditional hierarchy visualizations.
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