Hierarchies (Trees) Definition Examples Data repository in which cases are related to subcases Examples Family histories, ancestries File/directory systems on computers Organization charts Animal kingdom: Phylum,…, genus,… Object-oriented software classes ... 9/17/2018 Shengdong Zhao @ UofT

9/17/2018 Shengdong Zhao @ UofT

2 Main Approaches Connection (node & link) Containment (node in node) outliner Containment (node in node) Venn diagram A B C A B C 9/17/2018 Shengdong Zhao @ UofT

Tasks Help understand node characteristics or tree structure? Some kinds of tasks: Find a node Revisit node List node ancestors Understand local topology Understand global topology Different Trees are good for different tasks 9/17/2018 Shengdong Zhao @ UofT

Why is tree visualization hard? Structure AND items (Structure harder, consumes more space) Scaling: data size grows very quickly (exponential) #nodes = bheight How to provide Context (when focus changes) May be multiple hierarchies May be multiple focuses 9/17/2018 Shengdong Zhao @ UofT

Current Status Many 2D and 3D hierarchy visualizations Each works for some tasks and some scales Very few have had user testing 9/17/2018 Shengdong Zhao @ UofT

Node-Link Diagrams 9/17/2018 Shengdong Zhao @ UofT

Tree 9/17/2018 Shengdong Zhao @ UofT

Distortion: Graphical Fisheye - 1992 Sarkar & Brown, DEC SRC, CHI’92 Also a number of 2D network visualizations Graphical Fisheye by Sarkar & Brown at DEC SRC in 1992 Generalization of Furnas fisheye view to 2D graph layout Here the view on the right is the same structure, but focusing on node 48 9/17/2018 Shengdong Zhao @ UofT

Overview + Detail: PDQ Trees Overview+Detail of 2D tree layout Dynamic Queries on each level for pruning 9/17/2018 Shengdong Zhao @ UofT

PDQ Trees 9/17/2018 Shengdong Zhao @ UofT

Auto-arrangement + Thumbnail: Spacetree 9/17/2018 Shengdong Zhao @ UofT

Different Orientation & Refocus: Hyperbolic Trees Rao, “Hyperbolic Tree” http://startree.inxight.com/ Xerox PARC Inxight Focus+context 9/17/2018 Shengdong Zhao @ UofT

Space Optimized Tree Quang & Mao (InfoVis 2002) 9/17/2018 Shengdong Zhao @ UofT

3D: Cone Trees Robertson, “ConeTrees” 3D for focus+context Xerox PARC 9/17/2018 Shengdong Zhao @ UofT

Space-Filling Representation Each item occupies an area Children are “contained” under parent One example 9/17/2018 Shengdong Zhao @ UofT

Treemaps Shneiderman, “Treemaps” Vishal, Jeevak Maryland http://www.cs.umd.edu/hcil/treemap3/ Maryland 9/17/2018 Shengdong Zhao @ UofT

Variation: Cushion Treemap Add shading and texture to help convey structure of hierarchy Van Wijk ‘99 9/17/2018 Shengdong Zhao @ UofT

Sunburst Stasko, GaTech Radial layout Animated zooming 9/17/2018 Shengdong Zhao @ UofT

Sunburst vs. Treemap + Faster learning time: like pie chart + Details outward, instead of inward + Focus+context zooming - Not space filling - More space used by non-leaves All leaves on 1-D space, perimeter Treemap: 2-D space for leaves - Smaller scale? 9/17/2018 Shengdong Zhao @ UofT

CHEOPS Beaudoin, “Cheops” Jon, Mudita http://www.crim.ca/hci/cheops/index1.html 9/17/2018 Shengdong Zhao @ UofT

Challenges Multiple foci George Robertson, Microsoft Research 9/17/2018 Shengdong Zhao @ UofT

Time Tube - 1998 Chi et al., Xerox PARC, CHI’98 9/17/2018 In 1998, Chi et al at PARC introduced the Time Tube A sequence of Disk Trees used to visualize changes in a web site over time This is an example of viewing multiple similar hierarchies 9/17/2018 Shengdong Zhao @ UofT

Taxonomy Visualization - 2000 Graham et al., Napier Univ. IJHCS 2000 Recently, Graham et al at Napier Univ. explored visualizing changing biological taxonomies In this example, individual objects are tracked across the hierarchies Graham told me informally that this approach was abandoned when they tried to scale it up to real sized problems 9/17/2018 Shengdong Zhao @ UofT

MultiTrees - 1994 Furnas & Zacks, Bell Core, CHI’94 DAG’s with shared subtrees MultiTrees were introduced by Furnas and Zacks at Bell Core in 1994 They are basically large DAG’s with shared subtrees The typical example is about a class syllabus created by one professor A second professor reuses some of the material, but only a subset A third professor uses a different subset, possibly reusing some of the material introduced by the second professor 9/17/2018 Shengdong Zhao @ UofT

Polyarchies multiple inter-twined trees Visual pivot George Robertson, Microsoft Research 9/17/2018 Shengdong Zhao @ UofT

Research Questions Can multidimensional data per node be portrayed? How does the visualization scale? What tasks are best supported by each vis? Can users quickly understand the representation? 9/17/2018 Shengdong Zhao @ UofT

Observations Possible Solution It’s hard to preserve the structure of the tree and allow scalability Different approaches are good for certain tasks with certain scale, and one single approach often has limitations and can’t solve a range of problems well Change of representations require learning Possible Solution Try a hybrid approach to balance the structure and scalability Create a solution with continuous variations for a range of tasks Use animation to help users to understand the representation 9/17/2018 Shengdong Zhao @ UofT

Node Link vs. Space Filling Advantage of Node Link Show Structure and Item Natural Disadvantage: Hard to scale (100 nodes) Advantage of Space Filling Using 100% of screen space, scalable monitoring and detect patterns in leaf nodes Harder to see the structure 9/17/2018 Shengdong Zhao @ UofT

What about combining the two techniques to create a continuous series of smooth representations and use animation to help users to understand the these representations better 9/17/2018 Shengdong Zhao @ UofT

Several Ideas Create animated transition between linked tree and treemaps 9/17/2018 Shengdong Zhao @ UofT

Intermediates 9/17/2018 Shengdong Zhao @ UofT

Overview + Detail 9/17/2018 Shengdong Zhao @ UofT

Questions Is this a worthwhile research topic? Suggestions for further directions? Any other combinations? Which variation of the hybrid model is good for what tasks? (Scale?) Anything else? 9/17/2018 Shengdong Zhao @ UofT