Jakob Nielsen is the author of Hypertext and Hypermedia, a fine overview of the field which could be considered as a companion volume to this study. In "The Art of Navigating Through Hypertext," he writes:
Hypertext is non-sequential writing: a directed graph, where each node contains some amount of text or other information. [...] [T]rue hypertext should also make users feel that they can move freely through the information according to their own needs. This feeling is hard to define precisely but certainly implies short response times and low cognitive load when navigating. (298)