21.2 The genesis of hypertext

We do not intend this section to be a general overview of everything that has gone before. The reader who is interested in such a description would do well to read Jeff Conklin's

excellent review (Conklin, 1987), followed by Jakob Nielsen's popular book (Nielsen, 1990). Rather, we would like to present some of the historical highlights as being representative of three different conceptual stances, and we represent each of these by an influential figure in the field. These are:

• The human being as possessor of a cognitive system based on association: the view of Vannevar Bush
• Technology as an augmenter of the human intellect: the personal philosophy of Doug Engelbart
• The need for a flexible and usable access mechanism to the world of interrelated information: the dream of Ted Nelson

The article most often cited as the modern birthplace of hypertext is Vannevar Bush's "As We May Think" (Bush, 1945). Bush was appointed the first director of the Office of Scientific Research and Development by President Roosevelt in 1941. He saw clearly the problems associated with the everincreasing volumes of information that were the product of the Second World War research and technology initiatives:

There is a growing mountain of research. But there is increased evidence that we are being bogged down today as specialization extends. The investigator is staggered by the findings and conclusions of thousands of other workers conclusions which he cannot find time to grasp, much less to remember, as they appear. Yet specialization becomes increasingly necessary for progress, and the effort to bridge between disciplines is correspondingly superficial.

It surprises many people to learn that this statement was made 50 years agothe information explosion is not such a modern phenomenon after all! To cope with this plethora of information, Bush conceived the memex, a device " . . . in which an individual stores his books, records, and communications, and which is mechanized so that it may be consulted with exceeding speed and flexibility." More than a simple repository, the memex was based on the principle of association, the notion that all facts, concepts, and ideas are linked in the mind, and that any one knowledge chunk can act as a stimulus or trigger to remember another.

In devising a supporting technology of this kind, Bush sought to create a means of information storage and retrieval that was intuitive to the user by virtue of its similarity to the workings of the mind. The appeal to intuitive operation predates many of the arguments that have subsequently emerged in the design of information technology. For Bush, it was sufficient that a principle such as associationat that time a current view of the human cognitive systemwould satisfy the organizational requirements of information users, an approach to design that is also neatly mirrored in current human factors thinking. However, given the volume of information a person might need to handle and what we now know about the vagaries of human association (e.g., Howe, 1980), it appears unlikely to us that such a principle alone could act as a sufficient design constraint on a hypermedia system.

These objections aside, it is interesting that Bush viewed the need for system design in such a user-centered manner. Unfortunately, the technology of the day was not as developed as the ideas: Bush conceived of the memex as being microfilm based. Hence, his ideas lay dojrmant for at least 2 decades, waiting for the technology to catch up. However, it is still commonplace to hear hypertext spoken of as a "natural" information system and a viable model of the human mind.

Whereas Bush (and others) sought to devise systems based on cognitive equivalence, Doug Engelbart has been developing his conception of hypertext since the early 1960s by placing his emphasis on the augmenting or amplifying of human intellect (cf. Engelbart, 1963), as reflected in the naming of his system as Augment. Engelbart's first implementation was NLS (oN Line System), which was meant as an environment to serve the working needs of his Augmented Human Intellect Research Center at Stanford Research Institute. This was a computer-based environment containing all the documents, memos, notes, reports, and so forth, in addition to supporting planning, debugging, and communication. As such, NLS can be seen as one of the earliest attempts to provide a hypertext environment in which computer-supported collaborative work (CSCW) could take place.

Engelbart's pragmatic position is less concerned with modeling the information-processing tendencies of the human being than with extending them, although to some extent such a position is logically determined by an image of the mind that one is trying to enhance or augment. In conceptualizing the technology in this way, Engelbart espoused the notion of hypertext as some form of cognitive artifact, extending the capabilities of the human being and offering the potential to attain performance levels in information tasks which would be difficult or impossible to achieve without hypertext. This is not dissimilar to McLuhan's ideas of technologies as extensions of human faculties, for example, wheels as an extension of legs (McLuhan, 1964), ideas that had their own philosophical roots in the "personal knowledge" work of Michael Polanyi (1957).

The actual term hypertext is attributed to Ted Nelson, who called his dream system Xanadua "docuverse" in which the entire literature of the world is linked, a "universal instantaneous hypertext publishing network" (Nelson, 1988). In Xanadu nothing ever needs to be written twice; a document is built up of original, or native, bytes and bytes that are transclusions, a term that implies the transfer and inclusion of part of one document into another. However, an important aspect of Xanadu is that the transclusion is virtual, with each document containing links to the original document rather than to copies of its parts.

While Nelson's view may appear to be the most ambitious, in many ways his advocacy gf this form of system is the most realistic, since it rests less on contemporary assumptions drawn from the psychological theories of the day and more on the requirement for a technology to provide rapid, easy access to the world of information. At an abstract level, the World Wide Web developed by Tim Berners-Lee and colleagues at CERN (Berners-Lee et al., 1994) comes close to realizing Nelson's dream, since it allows links between documents anywhere in the world (or at least anywhere with a connection to the Internet).l Indeed, this may be the route through which some of the ideas behind Xanadu will now be instantiated. When Autodesk, the CAD company, purchased Xanadu in 1988, there was hope that an actual product would be developed. However, 5 years and reputedly $5 million later, Autodesk has abandoned the project, and the Xanadu name is back with Nelson who, at the Hypertext '93 conference, was talking about "Xanadu Light" based on existing tools such as Gopher and Telnet.

The three views represented here are not mutually exclusive; it is possible to advocate a hypertext system that provides ready access to all information and therefore allows users to perform new tasks. Indeed, there is a fine line between these idealized positions, and it is not possible, or indeed very useful, to describe any particular contemporary system (or system designer's viewpoint) in terms of one or any of them. However, the fact that different views can proliferate illustrates the point that hypertext is not a unitary concept, not a single thing that can be defined any more precisely than in terms of nodes and links. It is for this reason that hypertext software packages with completely different "look and feel" (cf. Guide and HyperCard) can be produced and still claim to embody the concept of hypertext.

The corollary to this is that we should not expect any particular hypertext system to be ideal in all task situations. It is not surprising that Conklin's (1987) histogrical survey of hypertext systems groups them in a largely task-based way. He uses four categories: macroliterary systems, which center on the integration and ready accessibility of large volumes of information; problem exploration systems, which are designed to allow the interactive manipulation of information; systems for structured reading/browsing/reference; and, finally, systems that might have been applied to a specific application but whose real purpose in construction had been the experimental investigation of hypertext technology itself.

As we shall attempt to demonstrate here, the pedagogic implications of hypertext rest on a mixture of these three underlying philosophies. However, a major weakness of the field has been the inadequate theoretical explication of the nature of learning that hypertext systems might support. In particular, an oversimplistic acceptance of the naturalistic argument advocated by Bush remains, even if the models of the mind subscribed to by contemporary learning theorists (e.g., Greeno et al., 1978) are more sophisticated than the principle of association current in Bush's time. Consequently, the field lacks a dominant theoretical perspective that can draw on significant empirical support, and much of the literature in the field is rhetorical in style, reflecting the preparadigmatic nature of the field.

At the detailed level, there are still numerous important differences between Xanadu and the World Wide Web, the former including consideration of, for example, copyright payment, storage and usage charging, addressing to the character level, typed links, and, of course, transclusions.