11.4 XEROX Information Visualizer

This section presents a collection of tools addressing information exploration and navigational issues that have been developed at XEROX PARC. These navigation tools are somewhat more narrow in scope than the fish eye view concept in that each of the tools described here addresses one specific problem.

The work of Card, Mackinlay, and Robertson [Car91] [Mac91] [Rob91] is embedded into the larger context of trying to reorganize the office. In particular, they have targeted the organization of the desktop. Their system called Information Visualizer tries to provide an information workspace on the computer screen that allows the visual and spatial management of more information than is possible with current technologies. The information visualizer consists of three main components:

Card et al. introduce a virtual 3D room metaphor, where the user switches on the screen between different rooms to enlarge the immediate storage space [Car91]. The rooms metaphor avoids the cognitive overload problem by only showing the items in the active room. Figure I.60 shows an obvious 3D/Rooms example where the 3D structure of an office building is used to give immediate access to offices and their inhabitants through the computer.

Figure I.60 Information visualizer: 3D/Rooms example (ExFig Plate 2 from [Car91])
Cognitive Co-Processor:
To improve the human-computer interface for information retrieval, Card et al. have defined a user interface interaction manager based on the concept of semi-autonomous agents.
Information visualizations:
To visualize the information contained in 3D/Rooms, Card et al. have developed different information representation techniques. Figure I.60 shows the office building metaphor as an interface to people. In the next two paragraphs two other 3D information representation techniques, cone trees and the perspective wall, are introduced.
Cone Trees

Cone trees try to represent hierarchically structured information in a 3D space [Rob91]. The user controls the 3D environment with a conventional 2D device, normally the mouse. Nodes in a cone tree are either laid out horizontally or vertically. Figure I.61 shows a simple vertically oriented cone tree. The user can grab any of the nodes in the tree with the mouse and rotate the whole tree to bring the selected node to the foreground. The rotation of the tree is animated to give the user feedback of what is happening.

Figure I.61 Vertically oriented Cone Tree (ExFig Plate 2 from [Rob91])

Lighting cues like lighter coloring and shadows of the cones on the room floor improve the 3D perception. To hide parts of a complex hierarchical substructure, Robertson et al. use gardening operations. The user can prune or grow a substructure by manipulating a node either with a direct mouse gesture or by using a menu command. Cone trees have been used by Robertson et al. to visualize file directory structures, organization structures, and to visualize a company's operating plan. During user testing, Robertson et al. found that the most important component of the cone tree user interface was the animation capability. Animating tree modifications allows users to simultaneously understand the current operation. Without animation, it takes them a long time to reassimilate the structural relationships. Robertson et al. also found that the 3D representation permitted them to represent an order of magnitude more nodes on the screen than with a comparable optimized 2D representation.

Perspective Wall

While cone trees are used to visualize hierarchical information, the perspective wall represents linearly structured information [Mac91]. The perspective wall employs a simplified fish eye view strategy by representing the linear information in a 3D space and enlarging the current focus in the foreground and bending more distant data to the back (figure I.62).

Figure I.62 Perspective wall (ExFig Plate 2 from [Mac91])

This intuitive 3D metaphor for distorting 2D views allows the user a smooth transition between views. As with cone trees, the user can select an element in the perspective wall which is then moved to the center panel of the wall. This animation permits the user, similarly to cone trees, to reassimilate quickly to the modified view. The user is also able to change the level of detail by stretching the panel edges or the bent back sides of the panel.

The information representation techniques for the information visualizer exhibit some unique features not present in any other existing system. Unfortunately, today's hardware is barely powerful enough to provide the real time, high resolution 3D graphics needed for the information visualizer, as its interface runs on Silicon Graphics IRIS 3D graphics workstations. Nevertheless, the concepts and ideas described here may be guiding information management interfaces of the future, as ideas from XEROX PARC have already influenced the ways of computing frequently in the past.