Many different hypertext systems have been presented in the previous section. And each of them introduced new concepts. Even more confusing, each system comes along with its own terminology and might have a slightly different understanding of already existing concepts. For example a hypertext node is called (in alphabetical order) article, card, compound text, document, file, hyperdocument, node, page, parallel document, windowing text and writing space. The same variety of terms can be found for hyperlinks. A clear terminology is necessary to compare the presented hypertext systems with each other and to recognize significant variations.
A couple of approaches have been taken to classify the species of hypertext systems. First is Jeff Conklin 1987 with Hypertext: An Introduction and Survey [Conklin 87]. He presents a table that compares several Hypertext systems against a possible set of features.
The second approach is The Dexter Hypertext Reference Model [Halasz/Schwartz 94]. It grew out of a series of small workshops on hypertext between 1988 and 1990. The initial workshop was held at Dexters Inn in New Hampshire, hence the name for the model. Among the participants were Doug Engelbart (NLS/Augment), Frank Halasz and Randall Trigg (NoteCards), Janet Walker (Symbolics), Catherine Plaisant (Hyperties), and Norman Meyrowitz (Intermedia).
The most recent theory is on Open Hypermedia Systems. Intermedia, Hyper-G and especially Microcosm belong into this category.