Seeing the forest for the trees: hierarchical displays of hypertext structures

Most recent hypertext systems support hierarchy only as a restricted subset of directed graph structure. Consequently they do not provide many of the capabilities for graphical information hiding and structure manipulation that a tree makes possible. This paper describes display techniques developed for IGD, a hypertext system that supports the creation of large graphical documents whose arbitrary directed graph structure is embedded in a strict hierarchy. IGD offers the full generality of arbitrary keyworded links, while simultaneously allowing hierarchies to be easily manipulated and displayed with much of their structural detail selectively abstracted.