Hypertext features are available in a great variety of software. The packages we have evaluated provide examples of the most important structural paradigms. (Another classification scheme is provided by Rada.)
Card-based systems provide for fixed-size, full-screen nodes. Scrolling is not available; all of the text in the node must fit on the screen. Such software is based on the cue card or slide show metaphor, and is commonly used to create software demonstrations, simple front ends to command-based tools, interactive presentations, etc. We believe that the card metaphor is too limiting for most purposes, as it forces writers to chunk text into nodes which may be unnaturally small for the given document. Examples include HyperShell, HyperTies, HyperWriter!, and Orpheus.
HyperCard-like systems are based on the card paradigm, but add rich interface tools and an English-based scripting language. This last feature is the most important. The phenomenal success of HyperCard turned hundreds of thousands of computer users into computer programmers, almost without them realizing it. However, it is our belief that writers should not need to be programmers simply to explore the benefits of hypertext. Other examples include HyperPad, LinkWay, PLUS, and ToolBook.
Note that with continued development, few packages fall strictly into the card paradigm; it has proven too limiting. For example, HyperCard 2.1, Plus 2.5, and HyperWriter! 3.0 all allow for scrollable windows; text in a node is no longer limited to that which may be displayed on one screen. However, the default configuration of these packages still highly favours the card metaphor. They do not provide a rich environment for hypertext without programming. An exception is KMS, which takes the card paradigm to its logical limit.
Document-based systems focus on text editing and formatting single documents. They are often extensions to word-processors, and are not optimized for non-linear writing. Examples include FrameMaker and Guide.
Windowing systems provide a rich event-driven interface which allow multiple scrolling windows. Users will be familiar with this interface from operating systems such as Microsoft Windows and Mac System 7. Such environments provide readers with the ability to compare two pages of text, write notes while viewing a second page, and so on. We believe that such activities must be fluidly supported for the benefits of hypertext to become apparent. Examples include Dart, Folio VIEWS, gIBIS, Intermedia, Knowledge Pro, NoteCards, SmarText, StorySpace, and the Windows Help Compiler.
Monk et al. have investigated structural paradigms from the viewpoint of a reader's efficiency at completing a given task. They found that a single document in a scrolling window was a more efficient interface than either an outline view or a dual-window tiled display with paging. When a map showing structural information was added, the tiled interface was ranked highest.
In any case, window interfaces take longer to learn and are more difficult for novices to use. However, according to Tombaugh et al, experienced users perform better with such systems. The advantages of the window paradigm outweigh the greater learning time.
For more on hypertext usability, see Nielsen's chapter in Hypertext and Hypermedia (Chapter 9).