I have studied visualizing XML documents in order to create a visual XML editor. As part of this, I defined some research questions one answers when creating a new XML visualization. Existing XML editors and tree visualizations were analyzed using these research questions.
Three improvements of existing tree visualization techniques were presented:
Focus+context in Icicle plot, maximizing nodes in Cheops and Tabbed Treemaps. I also discussed the possibility to combine several visualizations. A new visual XML editor was created based on Tabbed Treemaps. The other presented visualizations were left for further research.
The new XML editor was evaluated and found to give an unprecedented view of XML documents. It enabled getting an overview of the structure of the document or a selected subtree. Although not using space optimally, the visualization was more effective in using screen space than current editors. I also gave directions on how to compact the visualization further.
When editing documents smaller than 100 kilobytes, users preferred using the implemented editor for navigating and searching the document over other XML editors they had tried. They were, however, unsure about how suitable it was for editing content as they were used to editing XML documents as text instead. No documents between 100 kilobytes and one megabytes (about 2000-20 000 lines) were evaluated. With documents larger than 1 megabytes navigating in the document and finding where most content was did not work well in the new editor. This was because the editor showed nodes as lines when they could not be shown using Tabbed Treemaps.
The largest files in the evaluation contained tree structures that were more wide than high. Files consisted of up to ten levels of elements but instead had over thousands of elements per level. Large XML documents were hard to edit because it became difficult to choose the wanted element from among several siblings. This problem was present in other editors also. Solving this problem can mean a breakthrough in editing large XML documents.
During evaluation several improvements were suggested for the created editor.
Three important issues without straightforward answers were found. I have discussed possible solutions for these issues but these should be validated by implementing them in the editor and performing a new evaluation.
Firstly, there is a problem with how to present a wide level that cannot be shown completely due to space constraints. A combination of using Squarified Treemaps and showing only every nth element could solve this problem. This would allow a user to navigate approximately to the correct position in the subtree before navigating sideways
to the correct element. Alternatively, nodes could be clustered and navigated to by expanding one cluster at a time.
Secondly, the current visualization does not show the height of elements clearly.
Shading in the frames or in the rectangle of the element could answer this need. Using shading in the rectangle, however, can hinder showing the content.
Thirdly, users want parts with much content to stand out from the visualization. As this problem occurs when elements are not shown using Tabbed Treemaps, the background color of the element can be used, as the element’s content is not necessarily shown. Alternatively, the size of an element can indicate the size of its subtree.
To summarize: There is a need to visualize XML documents in order to learn and navigate their structure. Tabbed Treemaps have been implemented in a new XML editor that has been found to outperform existing editors in showing the structure of XML documents. This motivates to continue developing the editor, starting from the suggested improvements.
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