"a Three Dimensional Browser for Visualizing Orthogonal Hierarchies" (using Only Two-and-a-half Dimensions) a Three Dimensional Browser for Visualizing Orthogonal Hierarchies (dsing Only Two-and-a-half Dimensions)

Using three dimensional graphics to visualize abstract data presents an interesting challenge because, by definition, there is no physical counterpart to abstract data; its extension into three-space is not due to the fact that it is the natural thing to do. Prior work in using three dimensional graphics to aid abstract data visualization has concentrated on increasing the quantity of data visualized, using the third dimension as a natural but symmetrical extension to the world of two dimensional layouts. Little has been done, however, to actually use it to capture the semantics of abstract data. This paper presents the notion of using the third dimension asymmetrically so that our familiarity with two dimensional layouts and our abilities to mentally group things confined to a plane are exploited, leaving the third dimension as a means to encode semantic information. A design principle is forwarded whereby the notion of orthogonality in an analytic sense (independence) is captured by using orthogonality in a geometric-and hence, visual-sense. Two systems that illustrate the design principle applied to two very useful areas are described: a visualizer for a set of data with multiple relationships defined over it and a visualizer for program structure and control flow in an object-oriented environment.