#SECTION# Tree #SECTION_END# #OWNER#jwanken@cs.umd.edu#OWNER_END# #AUTHOR# Wanken, James (jwanken@cs.umd.edu) #AUTHOR_END# #ALL_AUTHOR# jwanken@cs.umd.edu #ALL_AUTHOR_END# #BACKGROUND# Hierarchies, also know as tree structures, are collections of data nodes where each node has a unique parent (node above it in the hierarchy), but may have many siblings (nodes below it in the hierarchy). In general, the nodes and the links between them can have multiple attributes. The entire structure of the hierarchy and its encompassing relations is also usually relevant. Tasks can be applied to a single node, a link, a collection of nodes, or even to the entire structure. #BACKGROUND_END# #BACKGROUND# Hierarchical data is very diverse and is encountered in many forms. Hierarchies naturally arise in taxonomies, the structures of organizations, disk space management, genealogies, and the Dewey Decimal system. Uses of hierarchies are almost as vast, including: finding a particular node, viewing a node in the context of the entire hierarchy, examining the over-all structure and relations of the tree, and even finding duplicates or anomalies within the tree structure. #BACKGROUND_END# #BACKGROUND# The traditional presentation of hierarchies usually consist of a 2-D representation where child nodes are positioned under their parents in wedge-like formations. Representing trees in this manner severly limits both the depth and breadth of the tree that one can view at a single time. Furthermore, navigating and finding specific nodes in such a structure can be confusing, disorienting and downright frustrating. More recent visualization techniques attempt to show many more nodes, if not the entire tree itself, as well as providing mechanisms for navigation and searching which allows the user to keep the context of the entire tree in mind as well as reducing the disorientation. #BACKGROUND_END# #BACKGROUND# Hierarchies can be seen as a special case of networks, except the definition of hierarchies eliminates the possibilities of dual paths and cycles. Every node in a hierarchy also has a unique path to the root node which is not guaranteed to be the case with networks. Visualization of hierarchies is related to 3-D data, as many visualizations use 3-D graphics to render the results. Hierarchies are similiar to the multi-dimensional data since the nodes in hierarchies usually contain a fair number of attributes, but multi-dimensional data does not contain the intrisic hierarchy in the data that hierarchical data usually provides (e.g. folders and files on a disk). #BACKGROUND_END# #BACKGROUND# The major players in the hierarchical visualization are Xerox PARC, with their Cone Trees, and Hyperbolic Trees approachs, both of which have been copied or used as a basis for many other projects. Treemaps, is another significant representation in this genre, which was developed in the HCIL at the University of Maryland. #BACKGROUND_END# #CITATION# Carriere, Jeremy and Kazman, Rick, Interacting with huge Hierarchies: Beyond cone trees, Proc. IEEE Information Visualization '95, IEEE Computer Press, Los Alamitos, CA (1995), 74-81.

This report describes an augmentation of cone trees with graphical and interaction technieques: usage-based filtering, animated zooming, hand-coupled rotation, fish-eye zooming, coalescing of distant nodes, texturing, effective use of color for depth cueing, and the applications of dynamic queries. It also enhances the usefulness of cone tree visualization for large hierarchies by all but eliminating clutter.

#CITATION_END# #CITATION# Johnson, Brian, and Shneiderman, Ben, Tree-maps: A space-filling approach to the visualization of hierarchical information structures, Proc. IEEE Visualization '91, IEEE, Piscataway, NJ (1991), 284-291.

This technique of hierarchical information allows 100% utilization of the display space, while mapping the full hierarchy onto a rectangular region. This efficient use of space allows large hierarchies to be displayed in their entirety and facilitates the presentation of semantic information.

#CITATION_END# #CITATION# Lamping, John, Rao, Ramana, and Piroli, Peter, A focus + context technique based on hyperbolic geometry for visualizing large hierarchies, Proc. of ACM CHI'95 Conference: Human Factors in Computing Systems, ACM, New York, NY (1995), 401-408.

The essence of this scheme is to lay out the hierarchy in a uniform way on a hyperbolic plane and map this plane onto a circular display region. This approach makes components diminish is size as they move outwards, and the display allows an exponential growth in the number of components being viewed.

#CITATION_END# #CITATION# Asahi, T., and Shneiderman, B., Using treemaps to visualize the analytic hierarchy process, Information Systems Research, 6, 4 (December 1995), 357-375.
Abstract: The Analytic Hierarchy Process (AHP), a decision-making method based upon division of problem spaces into hierarchies, is visualized through the use of treemaps, which pack large amounts of hierarchical information into small screen spaces. Two direct manipulation tools, presented metaphorically as a "pump" and a "hook," were developed and applied to the treemap to support AHP sensitivity analysis. The problem of construction site selection is considered in this video. Apart from its traditional use for problem/ information space visualization, the treemap also serves as a potent visual tool for "what if" type analysis.

#CITATION_END# #CITATION# Chimera, R., Wolman, K., Mark, S., and Shneiderman, B. Evaluation of three interfaces for browsing hierarchical tables of contents. Technical Report CAR-TR-539, CS-TR-2620, University of Maryland, College Park (February 1991).

#CITATION_END# #CITATION# Furnas, George W., Generalized fisheye views. In Proceedings of the ACM SIGCHI Conference on Human Factors in Computing Systems, ACM (April 1986), 16-23.

#CITATION_END# #CITATION# Feiner, R. Seeing the forest for the trees: Hierarchical display of hypertext structures. In ACM Proc. COIS88 (Conf. on Office Information Systems), Palo Alto, CA (March 1988), 205-212.

#CITATION_END# #CITATION# Jungmeister, W. A., Turo, D. (Nov. 1992)Adapting treemaps to stock portfolio visualization, CS-TR-2996, CAR-TR-648, SRC-TR-92-120.
Abstract: Treemap visualization techniques are extended and applied to stock market portfolios via a prototype application. Designed to facilitate financial decision-making, the prototype provides an overview of large amounts of hierarchical financial data and allows users to alter aspects of the visual display dynamically. Treemap concepts are illustrated via examples which address common portfolio management needs.

#CITATION_END# #CITATION# Johnson, B., TreeViz: treemap visualization of hierarchically structured information, In: CHI '92. Conference proceedings on Human factors in computing systems, 369-370.

#CITATION_END# #CITATION# Koike, Hideki and Yoshihara, Hirotaka. Fractal approaches for visualizing huge hierarchies. In Proceedings of the 1993 IEEE Symposium on Visual Languages. IEEE (1993).
Abstract: This paper describes fractal approaches to the problems which associate with visualizing huge hierarchies. The geometrical characteristic of a fractal, self-similarity, allows users to visually interact with a huge tree in the same manner at every level of the tree. The fractal dimension, a measure of complexity, makes it possible to control the total amount of displayed nodes. A prototype visualization system for UNIX directories is also shown. Browsing hierarchical data with multi-level dynamic queries and pruning, International Journal of Human-Computer Studies 46, 1 (January 1997), 103-124.

#CITATION_END# #CITATION# Lamping, John, Rao, Ramana, and Pirolli, Peter, A focus + context technique based on hyperbolic geometry for visualizing large hierarchies, Proc. of CHI'95.

#CITATION_END# #CITATION# Mitchell, Richard, Day, Davis, and Hirschman, Lynette, Fishing for information on the internet, Proc. IEEE Information Visualization '95, IEEE Computer Press, Los Alamitos, CA (1995), 105-111.

#CITATION_END# #CITATION# Mukherjea, Sougata, Foley, James D., and Hudson, Scott, Visualizing complex hypermedia networks through multiple hierarchical views, Proc. of ACM CHI '95 Conference: Human Factors in Computing Systems, ACM, New York (1995), 331-337.
Abstract: Our work concerns visualizing the information space of hypermedia systems using multiple hierarchical views. Although overview diagrams are useful for helping the user to navigate in a hypermedia system, for any real-world system they become too complicated and large to be really useful. This is because these diagrams represent complex network structures which are very difficult to visualize and comprehend. On the other hand, effective visualizations of hierarchies have been developed. Our strategy is to provide the user with different hierarchies, each giving a different perspective to the underlying information space to help the user better comprehend the information. We propose an algorithm based on content and structural analysis to form hierarchies from hypermedia networks. The algorithm is automatic but can be guided by the user. The multiple hierarchies can be visualized in various ways. We give examples of the implementation of the algorithm on two hypermedia systems.

#CITATION_END# #CITATION# Nation, D.A., Plaisant, C., Marchionini, G., Komlodi, A. (May 1997) Visualizing websites using a hierarchical table of contents browser:WebTOC To appear in Proceedings of 3rd Conference on Human Factors and the Web, Denver, Colorado (June 12), 1997. CS-TR-3791, UMIACS-TR-97-41,CLIS-TR-97-08
Abstract: A method is described for visualizing the contents of a Web site with a hierarchical table of contents using a Java program and applet called WebTOC. The automatically generated expand/contract table of contents provides graphical information indicating the number of elements in branches of the hierarchy as well as individual and cumulative sizes. Color can be used to represent another attribute such as file type and provide a rich overview of the site for users and managers of the site. Early results from user studies suggest that WebTOC is easily learned and can assist users in navigating websites.

#CITATION_END# #CITATION# Rekimoto, Jun and Green, Mark,"The Information Cube: Using Transparency in 3D Information Visualization", Proceedings of the Third Annual Workshop on Information Technologies & Systems (WITS'93), (1993), 125-132.

#CITATION_END# #CITATION# Robertson, George G., Card, Stuart K., and Mackinlay, Jock D., Information visualization using 3-D interactive animation, Communications of the ACM 36, 4 (April 1993), 56-71.

#CITATION_END# #CITATION# Roberston, G.G., Mackinlay, J.D., and Card, S.K. Cone Trees: Animated 3D visualizations of hierarchical information, In Proceedings of SIGCHI'91, (1991), 189-194.

#CITATION_END# #CITATION# Sarkar, M., Brown, M. Graphical Fisheye Views. Communications of the ACM. 37, 12 (1994), 73-84.

#CITATION_END# #CITATION# Sarkar, Manojit,Snibbe, Scott, and Reiss, Steven . Stretching the rubber sheet: A metaphor for visualizing large structure on small screen. In Proceedings of the ACM Symposium on User Interface Software and Technology. ACM Press (Nov 1993).

#CITATION_END# #CITATION# Shneiderman, B. Tree visualization with tree-maps: A 2-d space filling approach. ACM Transactions on Graphics. (1992).

#CITATION_END# #CITATION# Turo, D. (April 1994) Hierarchical visualization with Treemaps: Making sense of pro basketball data, Video in CHI '94 Video Program, ACM, New York. A two page video summary also appears in ACM CHI '94 Conference Companion, (Boston, MA, April 24-28, 1994), 441-442. Video also available through HCIL as part of the 1993 HCIL Video Report.
Abstract: Treemaps support visualization of large hierarchical information spaces. The treemap generation algorithm is straightforward and application prototypes have only minimal hardware requirements. Given primary graphical encodings of area, color and enclosure, treemaps are best suited for the tasks of outlier detection, cause-effect analysis and location of specific nodesósatisfying user-specified criteriaóin their hierarchical context. Distortion effects extend treemap capabilities by emphasizing node relationships in the diagram.

#CITATION_END# #CITATION# Vicente, K.J., Hayes, B.C., and Williges, R.C., Assaying and isolating individual differences in searching a hierarchical file system. Human Factors. 29(3) (1987), 349-359.

#CITATION_END# #CITATION# Vroomen, Louis C., Beaudoin, Luc, and Parent, Marc-Antoine, Cheops: A Compact Explorer For Complex Hierarchies. Visualization Conference. San Francisco, (1996).

#CITATION_END# #USER# Web Surfer. #USER_END# #USER# Network Management. #USER_END# #USER# Anyone performing a directory search. #USER_END# #USER# Role managers and people who use organizational charts. #USER_END# #TASK# Obtain global relationships and structure from the entire hierarchy. #TASK_END# #TASK# Find the most recent common ancestor between two nodes. #TASK_END# #TASK# Find the path to a particular node from the root of the hierarchy. #TASK_END# #TASK# Find clusters, duplicates, relationships, and inheritance properties from the structure of the hierarchy. #TASK_END# #TASK# Discovering attributes (especially the size) of nodes or entire subtrees. #TASK_END# #PROJECT# CHEOPS. Centre de recherche Informatique de Montréal. The Cheops approach maintains context within a huge hierarchy, while simultaneously providing easy access to details. #PROJECT_END# #PROJECT# Visage. Maya design Group. Visage provides an environment for exploring, analyzing, and visualizing information. #PROJECT_END# #PROJECT# WebTOC. HCIL - University of Maryland. By following local links, WebTOC generates and displays a hierarchical representation of the documents local to the site in the standard web-browsing environment. #PROJECT_END# #PROJECT# Info Cube. Sony. This technique is based on the nested box metaphor and uses 3D interactions. #PROJECT_END# #PROJECT# TreeBrowser Abstract. HCIL - University of Maryland. Treeview is a traditional hierarchy viewing object using a link-node diagram. #PROJECT_END# #PROJECT# TreeMap. HCIL - University of Maryland. Treemaps are a novel visualization approach which completely utilizes the display as well as being able to place over 5,000 nodes on the screen. #PROJECT_END# #PROJECT# TreeViz. HCIL - University of Maryland. TreeViz is a Macintosh implementation of the Treemap concept. #PROJECT_END# #PROJECT# WebSpace. University of Minnesota. WebSpace is a program developed to visualize the connections between HTML documents. Several types of display are available. #PROJECT_END# #PROJECT# Webviz. Geometry Center - University of Minnesota. A web visualization tool that views the web as a graph with the nodes being pages and the links are represented as edges in the graph. #PROJECT_END# #PROJECT# Docuverse. Department of Information Science and Telecommunications - University of Pittsburgh. Docuverse represents a large document space in colored pie segments, somewhat similiar to the structures of treemaps. #PROJECT_END# #PROJECT# Webview. Department of Information Science and Telecommunications - University of Pittsburgh. Related to Docuverse, Webview provides a tree-based structural display of a smaller part of the file system or document space. #PROJECT_END# #PRODUCT# Hyperbolic Tree. VizControls from Inxight (spinoff from Xerox - PARC). Displays tree structures mapped to a hyperbolic space and which is visualized in a fixed screen space. #PRODUCT_END# #PRODUCT# Cone Trees. VizControls from Inxight (spinoff from Xerox - PARC). Provides a 3-D representation and navigation of tree structures. #PRODUCT_END# #PRODUCT# Winsurfer. HCIL - University of Maryland. Winsurfer is a Microsoft Windows implementation of the treemaps concept. #PRODUCT_END# #PRODUCT# HyperDir - Cygron. Visualizes your disk or directories in hyperbolic space. (Microsoft Windows implementation). #PRODUCT_END# #PRODUCT# Explorer - Microsoft. Allows you to visualize your directories in a hierarchical scrolling list. #PRODUCT_END# #VIDEO# Viewing websites using a hierarchical table of contents browser: WebTOC - David Natio (5:40). #VIDEO_END# #VIDEO# Dynamic Queries and Pruning for Large Tree Structures - Harsha Kumar. #VIDEO_END# #VIDEO# WinSurfer: Treemaps for Replacing the Windows File Manager - Marko Teittinen. #VIDEO_END# #VIDEO# Visual decision-making: using treemaps for the analytic hierarchy process - Toshiyuki Asahi, Ben Shneiderman, David Turo (8:34). #VIDEO_END# #VIDEO# Hierarchical visualization with Treemaps: making sense of pro basketball data - Dave Turo (10:47). #VIDEO_END# #VIDEO# TreeViz(TM): file directory browsing - Brian Johnson (10:04). #VIDEO_END# #VIDEO# Treemaps for visualizing hierarchical information - Ben Shneiderman, Brian Johnson, Dave Turo (11:25). #VIDEO_END# #VIDEO# Three strategies for directory browsing - Rick Chimera (10:30). #VIDEO_END# #VIDEO# Visualizing Large Trees Using the Hyperbolic Browser - J. Lamping, R. Rao, Xerox PARC. #VIDEO_END#