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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.
Steven Feiner (Fri,) studied this question.