>Note: This is a temporary version of this file, crudely >dumpted into ASCII text, losing illustrations that were >done with PC line and box drawing characters. Word Perfect > 4.2 for DOS was a long time ago! APPROACHING HYPERTEXT: COGNITIVE MODELS AND USABILITY OF AN ELECTRONIC BOOK TECHNOLOGY by Robert B. Stepno Submitted to the Faculty of Wesleyan University in partial fulfillment of the requirements for the degree of MASTER OF ARTS IN LIBERAL STUDIES May 27, 1988 Essay Advisor: Marc M. Sebrechts Acknowledgements This essay is dedicated to Russ Walter and the Wesleyan University Computing Center, whose courses and equipment brought me into the Graduate Liberal Studies Program, and to Marc Sebrechts and Mary Ferguson, who patiently helped me get out of it in the end. (Russ and company also brought me into the computer age, but it looks like there's no easy way out of that.) Special thanks to Howard Eglowstein of Buffalo, N.Y., and Hindsight, Inc., of Enfield, Connecticut, for capturing Ted Nelson on tape, for the use of desktop publishing facilities, and for technical support; to J. Scott Johnson of NTERGAID, R. John Slade of Knowledge Garden, and Michael Stanford of Personal Computer Support Group (PCSG), for donating hypertext programs for use in this and future writing projects, and to Owl International, whose Guide software first put hypertext on my computer screen. (The Bibliography includes a more complete list of computer software products mentioned in this essay, or used as research tools, writing tools, and distractions.) Preface To paraphrase a former President, "I am not a cognitive psychologist." Nor am I a computer scientist. Some tools of those professions are used or discussed in this essay, but not with a professional's skill or intentions. Rather than a scientific attempt to prove a formal thesis, this essay is a report from the borders of several fields--including cognitive science, computer science, education, communication, and writing. What do you call someone who engages in this sort of border-walking? By profession, I've been a journalist and technical writer, by education "an English major" and an anthropologist. At Wesleyan University such interfield activity is encouraged in a program called "Liberal Studies." Ted Nelson, whose work inspired this essay, uses the phrase "systems humanist."[1] It's not a title I expect to see in the help-wanted pages of the New York Times on graduation day, but I may put it on my resume, just in case. Bob Stepno May 27, 1988 =============================================================== Note: This is an ASCII text version of the original document, which made use of text-graphics and other illustrations that have not been converted to fit this format. The page numbering indicated in the Table of Contents refers to the "official" version of this paper filed as my final essay with the Graduate Liberal Studies Program at Wesleyan University. =============================================================== TABLE OF CONTENTS Acknowledgements. . . . . . . . . . . . . . . . . . . . . . i Preface . . . . . . . . . . . . . . . . . . . . . . . . . . ii PART I: HYPERTEXT . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 1 CHAPTER 1: HYPERTEXT IDEAS . . . . . . . . . . . . . . . . . 2 THE INFORMATION AGE . . . . . . . . . . . . . . . . . . . 3 HYPERTEXT PROPHETS: BUSH, ENGELBART AND NELSON. . . . . . . 4 Bush. . . . . . . . . . . . . . . . . . . . . . . . 5 Engelbart . . . . . . . . . . . . . . . . . . . . . 7 Nelson. . . . . . . . . . . . . . . . . . . . . . . 8 CHAPTER 2: NONSEQUENTIAL TEXT. . . . . . . . . . . . . . . 10 HYPERTEXT ON PAPER. . . . . . . . . . . . . . . . . . . . 10 WORDS ON COMPUTERS. . . . . . . . . . . . . . . . . . . . 13 Word processing . . . . . . . . . . . . . . . . . . 14 Databases and operating systems . . . . . . . . . . 15 Outline processors. . . . . . . . . . . . . . . . . 16 Figure 1: OUTLINING . . . . . . . . . . . . . . . . . . . . 17 TOWARD HYPERTEXT. . . . . . . . . . . . . . . . . . . . . 18 CHAPTER 3: HYPERTEXT SYSTEMS . . . . . . . . . . . . . . . 19 FROM AUGMENT TO ZOG . . . . . . . . . . . . . . . . . . . 19 INTRODUCING GUIDE . . . . . . . . . . . . . . . . . . . . 22 Structures. . . . . . . . . . . . . . . . . . . . . 25 Feedback. . . . . . . . . . . . . . . . . . . . . . 27 Graphics. . . . . . . . . . . . . . . . . . . . . . 30 HYPERTEXT FEATURES. . . . . . . . . . . . . . . . . . . . . 30 PART II: MODELS FOR HYPERTEXT . . . . . . . . . . . . . . . 34 Introduction. . . . . . . . . . . . . . . . . . . . . . . 34 "Three Rs": writing, reading and research . . . . . . . . 35 CHAPTER 4: WRITING AND HYPERTEXT . . . . . . . . . . . . . 37 MODELING THE WRITING PROCESS. . . . . . . . . . . . . . . 37 Figure 2: WRITING . . . . . . . . . . . . . . . . . . . . 38 APPLYING THE MODEL TO HYPERTEXT . . . . . . . . . . . . . 41 A. The Task Environment, with hypertext . . . . . . . . 41 B. Writing Processes, with hypertext . . . . . . . . . . 47 C. Long-term memory and hypertext . . . . . . . . . . . . 58 MENTAL MODELS FOR HYPERTEXT TOOLS . . . . . . . . . . . . 59 Tarzanning: a questionable model. . . . . . . . . . . . . 63 CHAPTER 5: RESEARCH, READING AND HYPERTEXT . . . . . . . . 68 A COGNITIVE MODEL OF READING. . . . . . . . . . . . . . . 68 Figure 3: READING . . . . . . . . . . . . . . . . . . . . 70 APPLYING THE MODEL TO HYPERTEXT . . . . . . . . . . . . . 73 A. The Task Environment, with hypertext. . . . . . . . . 74 B. The Reading Process, with hypertext . . . . . . . . 90 Figure 4: The Talmud as hypertext . . . . . . . . . . . . 93 VISIBILITY AND MENTAL MODELS. . . . . . . . . . . . . . . 98 Another model: "interactive fiction". . . . . . . . . . .100 CHAPTER 6: CONCLUSIONS AND SPECULATIONS. . . . . . . . . . 104 About text models for hypertext . . . . . . . . . . .104 About other models. . . . . . . . . . . . . . .. . .105 About the future of hypertext . . . . . . . . . . .107 About hypertext and liberal studies . . . . . . . .109 About the limitations of hypertext. . . . . . . . .112 About augmenting the mind . . . . . . . . . . . . .114 APPENDIX: SAMPLE TEXTS, MENUS AND SCREENS . . . . . . . . .117 BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . . . . . .126 NOTES =============================================================== PART I: HYPERTEXT Introduction This essay is an exploration of new (and not-so-new) ideas about reading and writing with computers, including suggestions for applying research on conventional reading and writing to recent developments in electronic text technology. Part I introduces that technology, which risks going by the name "hypertext" in an industry where the prefix "hype" suggests national advertising campaigns and expensive overstatement. The three chapters of Part I are an introduction to hypertext concepts and products, including the program called Guide from Owl International, Inc., which is used as an example throughout the essay (including Part II, which compares hypertext concepts to cognitive models of conventional reading and writing). CHAPTER 1: HYPERTEXT IDEAS With claims as grand as "you are participating in the birth of a new era," microcomputer companies have begun to promote "hypertext" concepts--the idea that the computer can be a more powerful tool for reading and writing than conventional printed texts. Hypertext programs use the computer screen to display documents and relationships between them in ways that cannot easily be represented on paper. The author or reader can use a variety of techniques to annotate, cross-reference and retrieve documents, creating or following trails of association through the computer's electronic memory. For more than 40 years, writers and technologists have proposed new ways to store and cross-reference our explosion of scientific literature, business documents, and other written information. But managing paperwork isn't the only goal of hypertext. Its early proponents discuss their larger goals in phrases like "expanding human memory" or "augmenting human intelligence." Today's increasingly powerful, inexpensive computers and new data-storage technology are helping software developers turn some hypertext ideas into reality. Realizing the larger goals is not a job for computer programmers alone. It will take cognitive scientists, teachers, readers and writers of all kinds, as well as designers, publishers, librarians and others who work with printed word. Toward that end, this essay by a non-programmer explores the ways we use and think about old-fashioned texts, and ways we might transfer that understanding to reading and writing hypertext. As examples, it discusses several hypertext systems, especially their usefulness for education and research. THE INFORMATION AGE Computer storage of texts (as well as numerical information) has been possible for four decades. Use of computers for text processing became widespread in the past dozen years, from the modern newspaper with its digitized typesetting facilities to the small office with its desktop word processing computers. Until recently the idea of keeping encyclopedias and reference libraries on computers implied large, expensive, systems that could be used only by highly trained individuals. Today's optical disc[2] storage (CD ROM, Compact Disc Read-Only Memory) makes such systems possible at a cost within the reach of schools, libraries, small businesses, and many individuals.[3] A coat-pocket-sized CD ROM can hold 550 megabytes, the equivalent of 150,000 text pages or two tall filing cabinets of business records (Laub, 1986). Hypertext is one of the most promising methods of using such new high-capacity storage media efficiently and creatively (Brown, 1986). On standard magnetic media, microcomputer hypertext products are already being used successfully for smaller documents, such as program documentation (Binder, 1988). HYPERTEXT PROPHETS: BUSH, ENGELBART AND NELSON Even a hypertext has to start somewhere. The term itself was coined by Ted Nelson in 1965. He credits Douglas Engelbart of Stanford Research Institute with independently arriving at similar ideas and inventing tools that made hypertext systems possible and practical. Engelbart and Nelson both point to a 1945 essay by Vannevar Bush as a predecessor of their ideas. The remainder of this chapter discusses the thinking of these three men, their goals and their models of how people work (or could work) with computers and the written word. Bush The idea of building an associative tool to cope with the information age did not begin with the computer. Vannevar Bush, President Roosevelt's science advisor, foresaw the basic elements of such a system in his 1945 Atlantic Monthly article, "As We May Think." Bush said that alphabetical and numerical indexing was becoming inadequate in the face of "the enormous mass of the common record," particularly scientific research papers. Our ineptitude in getting at the record is largely caused by the artificiality of systems of indexing . . . information is found (when it is) by tracing it down from subclass to subclass. . . . one has to have rules as to which path will locate it, and the rules are cumbersome. . . . The human mind does not work that way. It operates by association. With one item in its grasp, it snaps instantly to the next that is suggested by the association of thoughts, in accordance with some intricate web of trails carried by the cells of the brain. . . . (Bush pp. 14-15) The device Bush proposed, the "memex," would extend human memory by storing thousands of documents.[4] It would hold not only the owner's business correspondence, notes and memoranda, but newspapers, periodicals and full sets of reference works: legal decisions, patent records, medical case histories, historical and scientific literature. The memex user would construct a "trail" through the documents, cross-referencing them at a press of a button, or adding marginal notes and comments. The essential feature, Bush wrote, is "associative indexing," in particular "a provision whereby any item may be caused at will to select immediately and automatically another. . . . The process of tying two items together is the important thing. (Bush, p. 16) Bush predicted that "wholly new forms of encyclopedias will appear, ready-made with a mesh of associative trails running through them, ready to be dropped into the memex and there amplified." Great thinkers then would be able to pass on to future generations not only their additions to human knowledge, but the trail they followed in developing those ideas, he said. Engelbart Among those who read Bush's Atlantic Monthly article in 1945 was Douglas Engelbart, a navy radar technician about to return to civilian life. Engelbart became an electrical engineer and computer scientist, and set to work with the goal of using the new digital computers to "augment human intellect." He was among the first to foresee the value of interactive computer systems for text processing as part of his more general goal of improving comprehension and problem-solving through better information-handling devices. (Engelbart, quoted in Rheingold, p.182) Going a step beyond Bush, Engelbart described a portable device that could store in one of its memory cartridges "the equivalent of an unabridged dictionary." He invited his readers to consider the impact such a machine might have: What changes in language and methodology might not result? If it were so easy to look things up, how would our vocabulary develop, how would our habits of exploring the intellectual domains of others shift, how might the sophistication of practical organization mature (if each person could so quickly and easily look up applicable rules), how would our education system change to take advantage of this new external symbol- manipulation capability of students and teachers and administrators? (Engelbart, 1963; quoted in Rheingold, 1986, p. 186) In 1968, Engelbart demonstrated a prototype "oNLine System" or NLS that not only allowed him to manipulate text on a computer screen, but to navigate a network of documents by pointing at symbols with a "mouse" (his invention) and by opening windows on a display screen. The screen image was projected at 20 times its original size, large enough to be viewed by an auditorium audience with dramatic impact: His manipulations maneuvered the screen display and the audience's consciousness through categories of information, zoomed down into subcategories, broke them into their atomic components, rearranged them, then zoomed back up the hierarchy to meet the vocal narration at a key point in the story, when the words on the screen and the words coming from the narrator merged before branching off again. (Rheingold, 1985) Many of Engelbart's new ideas--word processing, partitioning a display into windows, outline processing and manipulation of icons with a mouse--have become general tools on small computers. Now they are also part of new microcomputer hypertext systems as well as large-computer hypertext systems including Engelbart's NLS/Augment. Nelson In a more roundabout fashion, Ted Nelson also decided in the 1950s to develop new tools for handling text with computers. His ideas for hypertext (he coined the term in 1965) grew out of his unfinished attempts to write a word processing program in college, and out of his personal need to organize notes and drafts for other unfinished projects ranging from film-making to a philosophical system. In one early article he described the main concepts of hypertext as ". . . a combination of natural language text with the computer's capacity for interactive branching, or dynamic display . . . of a nonlinear text." This kind of text, he observed, "cannot be printed conveniently on a conventional page." (Nelson, 1967) Nelson's hypertext, like Engelbart's NLS/Augment and Bush's memex, ultimately involves a grand design for extending our control of information. He proposes a master hypertext database called XanaduTM, able to link millions of documents world-wide (Nelson, 1981, 1988). As a software developer, Nelson most recently has focused on the Xanadu data structure, not the "front end" or user interface for hypertext programs. His books Literary Machines (1981) and Computer Lib/Dream Machines (1974, reprinted 1987) are experiments in using hypertext techniques between paper covers. Some of these techniques will be explored in the next chapter, along with the first hypertext computer programs. CHAPTER 2: NONSEQUENTIAL TEXT Hypertext systems combine new ideas about designing or structuring text with the technology of presenting text on a computer screen. This chapter discusses an early attempt at presenting hypertext design in a printed text (Ted Nelson's Literary Machines), and developments in word processing and the more hypertext-like outline processing. HYPERTEXT ON PAPER Literary Machines introduces the basic hypertext functions and the terminology used by most hypertext programs, including "buttons," "notes" and "links." Links associate two blocks of text in much the way that Bush described the memex's associative indexing. In a hypertext edition of this essay, for example, this paragraph could contain a link to part (or all) of the original text of Nelson's book. Link markers are frequently called "buttons," and can be specially marked words or graphic devices. For example, the words "See Nelson, 1987" could be used as a button linked to a large quotation, such as the following indented paragraphs (from Literary Machines) describing types of hypertext links. In a hypertext, the paragraphs could remain hidden from view unless the reader wanted immediate exposure to the primary source material. In this typed manuscript, our "link" choices are to use the convention of indenting a long quotation, to photocopy it and include it as an illustration or appendix, or simply to print a footnote[5] referring to this hard-to- find, privately published book.[6] LINKS ARE PART OF THE WRITING A link is simply a connection between parts of text or other material. It is put in by a human. Links are made by individuals as pathways for the reader's exploration; thus they are parts of the actual document, part of the writing. As perhaps the simplest type of link, a user may create book-marks--places he may want to re-enter text when returning to it. JUMP-LINK As another simple first example, let us simply think of a link as some sort of a jump opportunity, like a conventional footnote. An asterisk, say, signals that "there's something to jump to from here." If you point at it with your lightpen (or mouse or whatever), Bingo!--you're now at the footnote, or whatever else the author took you to. If you don't like it there, hit some sort of a Return Button . . . you are back where you were and no harm has been done. MARGINAL NOTES, SIDE-BY-SIDE WRITING Marginal notes are another simple and important type of link. (Where the "margin of the screen" is--that is, how to show them--is a matter particular to your own screen setup.) A user may also make side-by-side connections of other types. On contemplating any two pieces of text, he may make a link between them. Thereafter, when he displays either piece of text, and asks to see the links, a link-symbol is displayed, and the other attached text--if he wishes to see it. Naturally, making a marginal note consists of writing the note and hooking the link. HYPERTEXT The link facility gives us much more than the attachment of mere odds and ends. It permits fully non-sequential writing, or hypertext. (Nelson, 1981, p. 2/21) Literary Machines was originally published as a typewritten manuscript with simple pen-and-ink drawings.[7] The experimental hypertext book had several Chapters One, one Chapter Two, several Chapters Three, and instructions advising the reader to take various paths through the chapters--not to simply read it once from front to back. The pages of some chapters were split into "novice" and "expert" versions of the same material using dividing lines and different size type, as well as more conventional "links" in the form of footnotes and "see also" references. Readers were encouraged to read the book several times, "passing repeatedly through Chapter Two, until you understand this book." (Although the pages of Literary Machines were numbered, the book did not use another of sequential text's main tools for navigation and cross- referencing: it had no index.) WORDS ON COMPUTERS Although Literary Machines was a printed text, it emphasized that true hypertext would be electronic, that "Most, or 'all,' of our reading and writing can or will, in this century, be at instant-access screens" (Nelson, 1981, p. 1/2). But before there could be hypertext on computers, there had to be text on computers. Computers have been used to write, edit and store text since the development of the first programming languages. Into the 1970s, programmers gave instructions to the computer on punch cards or with line-printing teletype terminals. Separate programs made it possible to print "listings" of these texts with upper- and lower-case letters, paragraph formatting, variable margin settings, and other print characteristics. Other programs made it possible to send text between computers and through national and international networks of computers as "electronic mail." (See Rheingold, 1985, on the development of ARPANET, and Fuchs, 1983, on BITNET.) Text editors, word processing and electronic mail systems all offer basic text entry and editing capabilities, plus abilities to search for and change text. The early editors coped with limitations of the current data entry and display devices--card readers, teletypes and upper-case-only display screens. (See Schneider, 1974, for a chronicle of one humanist's experience with this rapidly changing technology.) Even as the displays improved, editor programs frequently kept the numbered lines and line-oriented editing commands of the earlier systems. Word processing In the past ten years, editing and print-formatting programs have been integrated into increasingly sophisticated "word processing" and "desktop publishing" systems. Today's computer screens not only display upper- and lower-case letters, but can simulate a wide variety of printed type fonts and sizes on screen. However, systems designed to send text to a printing device, often reflect the limitations as well as the abilities of the printer. For example, word processors commonly display text in the line-length, spacing and (with high-resolution screens) type font style of the printed version--none of which may be the optimum display for reading the text on screen. Electronic mail systems are designed for reading on screen, but since communication systems must be used by many different types of computers, they are frequently limited to displaying "lowest common denominator" text-- plain alphanumeric characters lacking even the simplest display attributes, such as underlining or bold type. The same is true of texts written for interpretation by the computer itself, such as a FORTRAN or Pascal program--only the plain text characters are used by the programming language's compiler or interpreter. Databases and operating systems In addition to displaying text, hypertext involves linking information. Computers also have been used to link texts to each other since the beginning of data processing. Database programs have the ability to connect items of information within and between files. Computer operating systems provide file management and (in the Apple Macintosh, for example) the ability to represent files of text information symbolically. Databases often use indexing and search techniques, rather than direct links, and usually involve information that can be broken into small pieces and stored in clearly defined fields. Some attempts have been made to use databases as writing tools (see Moore, Pfaffenberger) and to combine word processing and database programs, such as Nota Bene from Dragonfly Software. However, database programs do not approach the text-presentation and direct- link capabilities of hypertext software (Conklin, 1987). Outline processors An advanced form of word processing appeared on microcomputers in the mid-1980s, the hierarchical "outline processors." Such programs, include ThinkTank, Kamas, PC-Outline, and Framework. Engelbart's own Augment system includes hierarchical outlining among its features (Nelson, 1988). Outline processors provide dynamic display of texts, allowing blocks of text to be hidden behind an abbreviated display of section headings. The user can manipulate those blocks of text by moving the headings to new positions on the screen. The document can be viewed in many versions, depending on which blocks are "hidden" under their headings. For example, a term paper seen in an outline processor might appear as shown in Figure 1, below. Figure 1: OUTLINING At its topmost level, the outline looks like this: 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 � � � 1. Introduction � � � � 2. History � � � � 3. Future � � � � 4. Conclusions � � � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸 Expanded one level, the outline looks like this: 旼컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴커 � � � 1. Introduction � � � � 2. History � � 2.1 Eighteenth Century � � 2.2 Nineteenth Century � � 2.3 Twentieth Century � � � � 3. Future � � 3.1 Twenty-first Century � � � � 4. Conclusions � � � 읕컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴켸 Each numbered item in such an outline can represent additional subsections, any of which can contain dozens of pages of text. It takes only a few keystrokes to display the full text of a section or to add a new section heading called "Present" between "History" and "Future." The writer can move all of the 20-page "Twentieth Century" chapter under the new "Present" section heading by relocating the single line of text shown on the screen. If the user changes the order of outline sections, most out- line processors renumber the sections automatically. A similar "substitution" technique in which one block of displayed text can be exchanged for another longer (or shorter) block is common in hypertext programs, with or without hierarchical outline numbering. TOWARD HYPERTEXT Outline processors, word processors, and database file managers might seem wonderful tools to Vannevar Bush, but they are still not as powerful as his "memex" proposal. And they are not yet hypertext as defined by Ted Nelson. Speaking at a computer conference in 1987, Nelson said he considered word processing and outline processing when first proposing hypertext twenty years earlier, but he had dismissed the ideas in favor of something "grander." Word processors and outline processors would be confined to the sequential, hierarchical structure of numbered pages and outlines. "There is no reason anymore to suppose sequen- tiality. . . . There is no need for there to be numbered pages on the documents we read from our screens," Nelson said, ". . . The future of our entire literature lies on screens of different sorts."[8] CHAPTER 3: HYPERTEXT SYSTEMS FROM AUGMENT TO ZOG Since Ted Nelson introduced the term, hypertext and near-hypertext programs have been developed for large and small computers. They include Intermedia, which is providing resource texts for Brown University literature and biology courses (Yankelovich, Meyrowitz and van Dam, 1985; Yankelovich, 1987); HyperTIES (The Interactive Encyclopedia System)[9], which has given novice computer users information about museum and gallery exhibits (Marchionini and Shneiderman, 1988); and WE (Writing Environment) being used at the University of North Carolina at Chapel Hill to test cognitive models of writing (Smith et. al., 1986). Other influential systems include ZOG at Carnegie-Mellon University[10] (McCracken and Akscyn, 1984), Engelbart's NLS/Augment and Xerox's Notecards, among others. (For a comprehensive survey, see "Hypertext: An Introduction and Survey" by Jeff Conklin, published in IEEE Computer, September, 1987; or in expanded form as a research report, A Survey of Hypertext, from Microelectronics and Computer Technology Corp., December, 1987.) Owl International, Inc., introduced Guide for the Apple Macintosh in 1986 and for the IBM PC in 1987, calling the program "the first commercially available 'hypertext' system for personal computers." Apple brought hypertext to a much wider audience when it began giving away a product called HyperCard with each new Macintosh in August, 1987. HyperCard combines hypertext concepts with a simple text editor, a sophisticated graphics editor, and a programming language. As its name suggests, HyperCard uses an index card or "Rolodex" metaphor, with each screen-sized display representing a "card" of text and pictures. Cards can be grouped into "stacks" and linked using text or graphic "buttons." Selecting a "next card" button, for example, displays the next card in the stack. Buttons can be programmed to link other stacks, run programs, or control a device, such as a telephone dialer or video disc player. The card metaphor has been used frequently for microcomputer datafile programs (e.g., Zoomracks, CardBox, 3x5 and MultiMate On-File), but such programs do not have the linking, object-oriented graphic interface or programming capabilities of HyperCard. Apple's "bundling" of HyperCard with its computers generated a great deal of interest in the product and hypertext in general. Ironically, this first widely-used "hypertext" program has limited ability to deal with long texts. Its index-card or slide show style of presentation is more suited to smaller chunks of information. Other hypertext programs were introduced after the widespread publicity[11] about HyperCard. Many of these are HyperCard "stacks" including databases and programs developed with Apple's new HyperTalk programming language. New programs for the IBM PC or PS/2, include NTERGAID's Black Magic and Knowledge Garden Inc.'s KnowledgePro, a programming language that is now advertised as a "HypertExpert System." Macintosh adaptations of several of the university-based mainframe systems also have been reported in trade publications in recent months, but these programs are not yet widely marketed. Unlike most of these systems, Guide is available on both IBM and Apple Macintosh computers, has been nationally advertised, and is designed to handle large text documents. For those reasons, it is an appropriate vehicle to use in this discussion of hypertext and its potential for research, education and personal use. The version of Guide designed for the IBM Personal Computer can be used on dozens of brands of machines that use the Microsoft Windows operating environment.[12] Guide provides most of the examples in this essay. HyperCard and other systems provide examples of some techniques not present in Guide. INTRODUCING GUIDE Guide is sold as a hypertext "authoring system," a tool with which the user can create as well as read hypertext documents. Owl International also provides special versions of Guide to developers of software HELP systems or CD ROM document libraries, the original application for which the program was developed (Brown, 1986). The standard commercial Guide package for Microsoft Windows includes sample documents, a tutorial and an on- screen "help" system, all written in Guide. For the Macintosh, Guide has a read-only version called a Guide Envelope, which has been used to "publish" documents in Guide hypertext format, including an edition of Ted Nelson's Literary Machines. Like all programs that operate on the Macintosh or in the Windows environment, Guide uses a hand-held "mouse" pointing device and displays text, menus and graphics on a high-resolution screen. Rolling the mouse on a horizontal surface moves a pointer on the screen; pressing a button on the mouse selects the menu item, icon, or text at the pointer. Guide and HyperCard both call objects on screen that control hypertext functions "buttons." Hence "clicking on a button" means pointing at a button on screen, then pressing and releasing the physical button on the mouse. A Guide button can be a word or phrase, a larger block of text, or an imported graphic image.[13 Guide treats the beginning and ending points of a button as part of the linear stream of characters in the computer file, like a set of quotation marks. As such, a text button can be moved if its page or paragraph is edited. In contrast, a HyperCard button marks a fixed location on the Macintosh screen, like a transparent overlay, and does not respond if the text at that location is moved. Despite its text orientation, Guide is not a word processing[14] system. It is primarily designed to display documents on a computer screen, although it does have basic printing features. Through Microsoft Windows, it allows the user to view several documents at once, and to change the size and position of each document "window" on the screen. Guide automatically wraps each line of text to fit within a new window size, and can temporarily magnify or reduce the characters. While this flexibility enhances the user's ability to read text on the screen, Guide has few of the print- oriented screen formatting features of many word processors, such as centering or justified text. It also lacks a common text-entry and editing feature--use of the IBM keyboard's cursor arrow keys instead of the mouse. (Word processing conventions are discussed in more detail in the next chapter, concerning cognitive models for working with text on computers.) The reader and writer of a Guide hypertext document interact with Guide in the same ways--by choosing commands from seven pull-down menus named at the top of the screen, and by clicking on hypertext buttons. To select a command like MAKE BUTTON the user points to a menu heading (MAKE), presses the mouse button to show the command list, and drags the mouse pointer down the list of one- or two-word command titles to the desired one (BUTTON). Releasing the mouse button executes the selected command. Moving the pointer off the menu without releasing the button cancels the command. (See the Appendix for a listing of Guide's menus and commands, and for examples of the structures and control devices discussed below.) Structures Guide's three main hypertext structures are called Replacements, Notes and References. A fourth structure, the Inquiry, is a group of Replacements. The user is kept informed of the status of the document (whether buttons are present, open or closed) through a variety of feedback mechanisms. Buttons in Guide documents can be text strings or graphic images. Buttons can look like bold-faced, underlined or italicized words, or they can be any kind of icon or image the writer's graphics programs can create. Each of the three main hypertext structures has a distinctive butto