Hypertext: an Introduction and Survey

SURVEY & TUTORIAL SERIES

Hypertext: An Introduction and Survey

Jeff Conklin Microelectronics and Computer Technology Corp.

ost modern computer sys- design issues that go into fashioning a tems share a foundation hypertext environment. M which is built of directories The concept of hypertext is quite sim- containing files. The files consist of text Hypertext systems ple: Windows on the screen are associated which is composed of characters. The text with objects in a database, and links are that is stored within this hierarchy is linear. feature machine- provided between these objects, both For much of our current way of doing graphically (as labelled tokens) and in the business, this linear organization is suffi- supported links-both database (as pointers). (See Figure l.) cient. However, for more and more appli- within and between But this simple idea is creating much cations, a linear organization is not excitement. Several universities have adequate. For example, the documenta- documents-that open created laboratories for research on hyper- tion of a computer program * is usually exciting new text, many articles have been written about either squeezed into the margins of the the concept just within the last year, and program, in which case it is generally too possibilities for using the Smithsonian Institute has created a terse to be useful, or it is interleaved with demonstration laboratory to develop and the text of the program, a practice which the computer as a display hypertext technologies. What is all breaks up the flow of both program and communication and the fuss about? Why are some people will- documentation. ing to make extravagant claims for hyper- As workstations grow cheaper, more thinking tool. text, calling it "idea processing" and "the powerful, and more available, new possi- basis for global scientific literature"? bilities emerge for extending the tradi- In this article I will attempt to get at the tional notion of "flat" text files by essence of hypertext. I will discuss its allowing more complex organizations of advantages and disadvantages. I will show the material. Mechanisms are being that this new technology opens some very devised which allow direct machine- exciting possibilities, particularly for new supported references from one textual pioneers of hypertext, once defined it as "a uses of the computer as a communication chunk to another; new interfaces provide combination of natural language text with and thinking tool. However, the reader the user with the ability to interact directly the computer's capacity for interactive who has not used hypertext should expect with these chunks and to establish new branching, or dynamic display ... of a that at best he will gain a perception of relationships between them. These exten- nonlinear text ... which cannot be printed hypertext as a collection of interesting fea- sions of the traditional text fall under the conveniently on a conventional page." I tures. Just as a description of electronic general category of hypertext (also known This article is a survey of existing hyper- spreadsheets will not get across the real ele- as nonlinear text). Ted Nelson, one of the text systems, their applications, and their gance ofthat tool, this article can only hint design. It is both an introduction to the at the potentials of hypertext. In fact. one "Documentation is the unexecutable English text world of hypertext and, at a deeper cut, a must work in current hypertext environ- which explains the logic of the program which it accompanies. survey of some of the most important ments for a while for the collection of fea-

September Tsx? 0018-9162/87/0900-0017$01.00 <01987IEEE 17

ful to have a sense of the central aspects of using a hypertext system, particularly if you have never seen one. Below is a list of Display screen with browser the features of a somewhat idealized hypertext system. Some existing systems have more features than these, and some have fewer or different ones. • The database is a network of textual (and perhaps graphical) nodes which can be thought of as a kind of hyperdocument. • Windows on the screen correspond to nodes in the database on a one-to-one \ basis, and each has a name or title which \ \ is always displayed in the window. How- \ \, ever, only a small number of nodes are , ever "open" (as windows) on the screen at ,, the same time. , • Standard window system operations ,, are supported: Windows can be reposi- \, tioned, resized, closed, and put aside as \ \ \ small window icons. The position and size \ of a window or icon (and perhaps also its ,---- -;------,, color and shape) are cues to remembering I the contents of the window. Closing a win- " I I dow causes the window to disappear after \ " , I any changes that have been made are saved I to the database node. Clicking with the I I mouse on the icon of a closed window I I causes the window to open instantly. • Windows can contain any number of I I link icons" which represent pointers to I I other nodes in the database. The link icon I I contains a short textual field which sug- I I gests the contents of the node it points to. Clicking on a link icon with the mouse I I causes the system to find the referenced L ~ node and to immediately open a new win- Hypertext database dow for it on the screen. • The user can easily create new nodes and new links to new nodes (for annota- Figure 2. The screen at the top illustrates how a hypertext browser provides a direct tion, comment, elaboration, etc.) or to two-dimensional graphic view of the underlying database. In this illustration, the existing nodes (for establishing new con- node "A" has been selected for full display of its contents. Notice that in the nections). browser view you can tell not only which nodes are linked to A but also how the • The database can be browsed in three subnetwork fits into the larger hyperdocument. (Of course, hyperdocuments of any ways: (1) by following links and opening size cannot be shown all at once in a browser-only portions can be displayed.) windows successively to examine their contents, (2) by searching the network (or part of it) for some string, ** keyword, or attribute value, and (3) by navigating around the hyperdocument using a browser that displays the network graphically. The user can select whether the nodes and links display their labels or not. of hypertext systems. As the hyperdocu- Using a browser can be likened to using The browser is an important component ment grows more complex, it becomes dis- visual and tactile cues when looking for a tressingly easy for a user to become lost or certain page in a book. Sometimes we °Note that I am are describing two uses of icons: those disoriented. A browser displays some or all remember the general way the page looked that function as placeholders for windows that have of the hyperdocument as a graph, provid- and about how far it was through the been temporarily put aside, and those within windows that represent links to other nodes. ing an important measure of contextual book, although we don't recall the page and spatial cues to supplement the user's number or even which keyword terms model of which nodes he is viewing and would help us find it by using the index or ··A string is a series of alphabetic and numeric charac- how they are related to each other and their ters of any length, for example "listening" or table of contents. The browser display can "000274." neighbors in the graph. (See Figure 2.) be similarly scanned and scrolled when the

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Table 1. Hypertext systems and their features.

Hierarchy Graph- Link Attri- Paths Ver- Proced- Keyword Text Con- Pictures Graphical based Types butes sions ural or Editor current or Browser Hypertext Attach- String Multi- Graphics Systems ment Search users Boxer Yes Yes Fixed' No' No No Yes Yes Emacs No Yes Yes

CREF Yes Yes Yes No No By link No Yes Zmacs No Yes No

Emacs INFO Yes No No No No No No Yes Emacs No No No

IBIS Yes Yes Yes No No By link No No A basic Yes No No text editor

Intermedia Yes Yes Yes Yes No' No No' Yes Custom Yes Yes Yes

KMS Multiple Yes Fixed No No' Yes Yes Yes Text! Yes Yes No graph. WYSIWYG

Neptune Yes Yes Yes Yes No Yes Yes Yes Smalltalk- Yes Yes Yes 80 editor

NLS/ Augment Yes Yes Yes Yes Yes Yes Yes Yes Custom Yes Yes No

NoteCards Multiple Yes Yes Nodes No No Yes Yes Interlisp Yes Yes Yes

Outline Processors Yes No No No No No No Yes Various No No No

PlaneText Unix Yes No No No No No Unix/ SunView Yes Yes Yes file sys. grep text ed.

Symbolics Yes Yes No No Yes No No Yes None No No No Document Examiner

SYNVIEW Yes No No No No No No No line.ed.! No No No Unix

Textnet Multiple Yes Yes Yes Yes No No Keyword Any No No No

Hyperties No Yes No No No No No No' A basic No Yes No text editor

WE Yes Yes No Fixed No' No' No' No Smalltalk- No' Yes Yes 80 editor

Xanadu No Yes Yes Yes Yes Yes No No Any No Yes No

ZOG Yes No No No No No Yes Full text Spec. Pur. Yes No No

I Can be user programmed. z Planned for next version.

In this table, each column represents one possible feature or ability that a hypertext system can provide. The negative or affirmative entries in the table indicate whether the corresponding hypertext system meets the standard criteria for a specified feature. These criteria are listed below.

Hierarchy: Is there specific support for hierarchical structures? Graph-based: Does the system support nonhierarchical (cross-reference) links? Link types: Can links have types? Attributes: Can user-designated attribute/value pairs be associated with nodes or links? Paths: Can many links be strung together into a single persistent object? Versions: Can nodes or links have more than a single version? Procedural attachment: Can arbitrary executable procedures be attached to events (such as mousing) at nodes or links? String search: Can the hyperdocument be searched for strings (including keywords)? Text editor: What editor is used to create and modify the contents of nodes? Concurrent multiusers: Can several users edit the hyperdocument at the same time? Pictures or graphics: Is some form of pictorial or graphical information supported in addition to text? Graphics browser: Is there a browser which graphically presents the nodes and links in the hyperdocument?

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multiperson distributed conferenc- ing/editing. NLS has evolved over the years. It is now called Augment (or NLS/ Augment) and is marketed as a commercial network system by McDonnell Douglas. In developing NLS, the emphasis has been on creating a consistent environment for "knowledge workers" (that is, office automation for software engineers). The system now includes many forms of computer-supported communication, both asynchronous (email with links to all documents, journaling of ideas and exchanges, bulletin boards, etc.) and syn- chronous (several terminals sharing the same display, teleconferencing, etc.). It includes facilities for document production and control, organizational and project information management, and software engineering. (See Figures 3 and 4.)

Nelson's Xanadu Project. During Engelbart's development of Augment, another hypertext visionary, Ted Nelson, was developing his own ideas about aug- mentation, but with an emphasis on creating a unified literary environment on a global scale.Nelson coined the term "hypertext." His thinking and writing are the most extravagant of any of the early Figure 4. Augment display showing five windows. Window 1 (W-l) has a passage workers. He named his hypertext system as if embedded in a message, showing a link to Branch 7c of Document 2250 in the Xanadu, after the "magic place of literary OAD Journal. AViewSpec ("ebtzgm") provides the following specifications: tar- memory" in Samuel Taylor Coleridge's get level plus one, truncate to one line per statement, no blank lines between state- poem "Kubla Khan." In Xanadu, storage ments, show only that branch (e.g., not Branch 7d), and turn on Location space is saved by the heavy use of links. Numbers. Window 2 (W-2) shows the view obtained with a jump link command. Only the original document and the To perform a jump link command, the operator clicks on the link in W-l, then changes made to it are saved.The system moves the cursor into W-2 for the final click. The very top-left system message easily reconstructs previous versions of announces that the desired Journal Item has been accessed, and the cluster at the documents. Nelson describes his objec- top left of the screen verifies that the view is clipped to three levels and the state- tives as follows: ments truncated to one line each. Window 3 (W-3) shows an indirect link that specifies the linkage path. In effect, this link says "go to the statement in the file Under guiding ideas which are not technical but literary, weare implementing a system for named 'Ref-6,' follow the link found there to its target file, and in that file find storage and retrieval of linked and window- Location Number 6."Note that the same ViewSpec is specified here as for the link ing text. The document, our fundamental in W-l. Window 4 (W-4) identifies Ref-6 and provides its general reference source unit, can have windows to any other docu- as the reference section at the end of the document; a user can jump from the link ments. The evolving corpus is continually expandable without fundamental change. citation in W-3 to see this statement by using the jump name command. To per- New links and windows can continually add form this command, he clicks on "Ref-6" in W-3 then clicks on W-4. Window 5 new access pathways to old material.Fast (W-5) shows a view in the OAD-Journal Item 2250.The user can obtain this view proprietary algorithms render the extreme by performing a jump link command on the indirect link of W-3. To perform this data fragmentation tolerable in the planned command, the user clicks on the indirect link of W-3 and then clicks in W-S. back-end service facility. 5

The long range goal of the Xanadu project has been facilitating the revolutionary process of placing the entire world's liter- tainable, and that a system for the elec- The back end of the Xanadu system has ary corpus on line. In fact, Xanadu's tronic accounting and distribution of been implemented in Unix and is available design makes a strong separation between royalties is in place.Nelson predicts that in several forms, induding as an on-line the user interface and the database server, the advent of on-line libraries will create service (much like Engelbart's Augment). with most of the emphasis placed on the a whole new market for the organization A crude front end for the Xanadu system latter. In particular, great care has been and indexing of this immense information is also available which runs on Sun work- taken that copyright protection is main- store. stations.

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hand. The function of this debate is not to arrive at specific conclusions, but rather to collect and order the best available evidence on each topic."

UNC's WE. A group at the University of North Carolina at Chapel Hill has been developing a writing environment called WE.9 Their research is based on a cognitive model of the communication process which explains reading as the process of taking the linear stream of text, compre- hending it by structuring the concepts hierarchically, and absorbing it into long-term memory as a network. Writing is seen as the reverse process: A loosely structured network of internal ideas and external sources is first organized into an appropri- ate hierarchy (an outline) which is then "encoded" into a linear stream of words, sentences, etc. WE is designed to support the upstream part of writing. It contains two major view windows, one graphical and one hierarchical, and many specialized commands for Question moving and structuring material (nodes and links with attached text) between these two views. Normally a writer will begin by creating nodes in the graph view, where he can place them anywhere within the window. At this stage, little or no structure is imposed on the conceptual material. The writer can place nodes in "piles" if they seem to be related, or he can place individual nodes between two piles if they are somewhat related to both.As some con- Figure 5.A segment of a possible IBIS-style discussion showing the topology of the ceptual structure begins to emerge from IBIS network. Each node contains information on the type of the node, the time this process, the writer can copy nodes into and date of creation, the author, a short phrase describing the content, a longer the hierarchy window, which has special- body of text with the text of the comment, a list of keywords, and a list of the ized commands for tree operations. The incoming and outgoing links. hierarchy window has four different display modes: (1) the tree can be laid out on its side, with the root node on the left; (2) come with further experiments and opening up just those entries that are rele- the tree can be hung vertically with the root analysis. vant or useful to the idea that he is work- at the top; (3) child nodes can be displayed ing on. In addition, each outline entry can inside their parent node; and, (4) the hier- Outline processors. An outline proces- have a textual body of any length archy can be shown in the traditional out- sor is a word processing program which is associated with it, and the user can make line view. specialized for processing outlines, in that this body appear or disappear with a sin- WE uses a relational database for the its main commands deal with movement gle keystroke. This feature is a real boon storage of the nodes and links in the net- among, creation of, and modification of to the writing process, because it allows the work. The user points with a mouse to outline entries. In this respect, these pro- user to have a view of both the immediate select a node. A third window is an editor grams commercialize many ideas from text that he is composing and the global for the material within the currently Engelbart's NLS/ Augment. Outline context for it. It also facilitates rapid selected node. A fourth window on the processors also have at least simple text movement between sections, particularly screen is for queries to the database. A editors and do some text formatting, so in large documents, because in outline fifth window is used to control system that the user can use the same tool to go mode a remote section is never more than modes and the current working set of from outline to finished document. One of a few keystrokes away. nodes. the most powerful features of outline Most outline processors are personal WE is designed to be an experimental processing is the ability to suppress lower computer programs, and they have done platform to study what tools and facilities levels of detail in the outline. As with much to bring some of the concepts under- will be useful in a writer's environment. Engelbart's NLS/ Augment, the user can lying hypertext into popularity. The first The real validation of these ideas, as with view just the top level of the outline, or the of these was called ThinkTank. It was so many of the systems described here, will top n levels, or he can "walk the tree," released in 1984. It has since been joined.

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which will provide string search. bookmarks, multiple windows, and user anno- tation.

Symbolics Document Examiner. The most advanced of the on-line help systems, this tool displays the pages from the entire twelve-volume manual set on the Syrn- bolics Lisp machine screen.l ' Certain textual fields in the document (printed in bold) are mouse-sensitive. Touching one of these fields with the mouse causes the relevant section of the manual to be added to the current working set of manual pages. The system allows the reader to place bookmarks on any topic and to move swiftly between bookmarked topics. The protocol for link following is tailored to browsing in a reference manual or ency- clopedia. Mousing a link only causes it to be placed on a list of current topics. Then, mousing an entry in this list causes that link to be followed, bringing up the referenced topic in the main viewing window. The system also supports on-line string search of preidentified keywords, includ- PLACES: AUSTRIA PAGE 10F3 ing the search for whole words, leading substrings. and embedded substrings. The Austria (see map) holds a special place in the history of the Holocaust. system is thus well designed for the specific task of browsing through a technical man- Situated between Eastern and Western Europe, possessing a vibrant and ual and pursuing several aspects of a tech- culturally creative Jewish community on the eve of World War II, nical question or several levels of detail simultaneously. The user cannot make any Austria had also provided the young Adolf Hitler, himself an Austrian changes or additions to the manual set (although it is possible to save personalized raised near Linz, with important lessons in the political uses of collections of bookmarks). antisemitism Leading Nazis came from Austria: the names of Adolf General hypertext technology. So far I Hitler, Adolf Eichmann, who organized the deportations of the Jews to have discussed hypertext systems that have particular practical applications. The fol- the death camps, and Ernst Kaltenbrunner, the head of the lowing systems also have one or more applications. but their primary purpose is Reich Main Office for Security, 1943-45, readily come to mind. As experimentation with hypertext itself as a technology. For example, while Linz - city in northern Austria; childhood home of Adolf Hitler and other NoteCards has been used for authoring, programming, personal information man- leading Nazis agement, project management, legal research, engineering design, and CAI, its NEXT PAGE RETURN TO GYPSIES INDEX developers view it primarily as a research vehicle for the study of hypertext.

Xerox PARe's NoteCards. Perhaps the Figure 6. The Hyperties Browser enables users to traverse a database of articles and best known version of full hypertext is the pictures by selecting from highlighted items embedded in the text of the articles. NoteCards system developed at Xerox The photos show the IBM PC version of Hyperties. The upper node shows a map PARC.14 The original motivation in of Austria. The lower node shows double-spaced text with link terms highlighted. building NoteCards was to develop an Either a touchscreen or jump-arrow keys are used for selection of brief definitions, information analyst's support tool, one full articles, or pictures. The Hyperties Author permits people with only word that would help gather information about processing skills to create and maintain databases.Research versions of Hyperties a topic and produce analytic reports. The run on the Enhanced Graphics Adapter to give more lines and multiple windows designers of Notecards observed that an and on the Sun 3 workstation to show two full pages of text at a time. Current information analyst usually follows a development efforts will enable readers to point at pictures and videodisc images to general procedure that consists of a series retrieve further information.

September 1987 27 project builds on two decades of work and pIe, it can show whole documents and the three prior generations of hypertext links between them, or each link and its systems. 16 approximate location within its docu- The first system was the Hypertext Edit- ments. (See Figure 8.) ing System designed by Ted Nelson, Andy The Intermedia project has a long his- For example, in the English literature course van Dam, and several Brown students for tory, many participants, and a serious the first time a student is searching for back- the IBM 2250 display in 1968. This system ground information on Alexander Pope, he institutional commitment to long-term was used by the Houston Manned Space- or she may be interested in Pope's life and the objectives. It conducts creative hypertext craft Center to produce Apollo documen- political events that prompted his satiric criti- experiments and uses the classroom as a tation. cism. To pursue this line of thought the stu- proving ground. Although this project is dent might retrieve the biography of Pope The second system was the File Retrieval and a timeline summarizing political events still in its early stages, we can expect it to and Editing System (FRESS). FRESS was taking place in England during Pope's life. contribute significantly to the develop- a greatly enhanced multiterminal Subsequently, the student may want to comment of effective cooperative work envi- timesharing version designed by van Dam pare Pope's use of satire with other later ronments based on hypertext. and his students.It became available in, authors' satiric techniques. This time the student may look at the same information about 1969 and was commercially reim- Pope but juxtapose it with information about Tektronix Neptune. Tektronix Neptune plemented by Phillips in the early 1970's. other satiricists instead of a time line. The is one hypertext system that has been par- FRESS was used in production by instructor (and other students, if permitted) ticularly designed as an open, layered hundreds of faculty and students over could read the student's paper, examine the architecture. 17 Neptune strongly separates reference material, and add personal anno- more than a decade. Its users included an the front end, a Smalltalk-based user inter- tation links such as comments, criticism, and English poetry class that did all of its read- suggestions for revision. While revising the face, from the back end, a transaction- ing and writing on a communal hypertext document, the student could see all of the based server called the Hypertext Abstract document. Like NLS, FRESS featured instructor's comments and examine the Machine (HAM). The HAM is a generic both dynamic hierarchy and bidirectional sources containing the counter-arguments. hypertext model which provides opera- reference links, and keyworded links and Like most of the serious workers on tions for creating, modifying, and access- nodes. Unlike NLS, it imposed no limits hypertext, the Intermedia team is espe- ing nodes and links. It maintains a on the sizes of nodes. On graphics termi- cially concerned with providing the user complete version history of each node in nals, multiple windows and vector with ways of managing the increased com- the hyperdocument, and provides rapid graphics were supported. plexity of the hypertext environment. For access to any version of a hyperdocument. The third project, the Electronic Docu- example, they contend that multiple links It provides distributed access over a comment system, was a hypermedia system emanating from the same point in a docu- puter network, synchronization for mul- emphasizing color raster graphics and ment may confuse the reader. Their alter- tiuser access, a complex network navigation aids. native is to have a single link icon in the versioning scheme, and transaction-based As part of Brown's overall effort to material (text or graphics) which can be crash recover)'. bring graphics-based workstations into quickly queried via the mouse to show the The interface layer provides several effective use within the classroom, the specific outgoing links, their names, and browsers: A graph browser provides a pic- Intermedia system is being developed as a their destination nodes. 15 They also pro- torial view of a subgraph of nodes and framework for a collection of tools that pose a construct called a web to implement links; a document browser supports the allow authors to create links to documents context-dependent link display.Every link browsing of hierarchical structures of of various media such as text, timelines, belongs to one or more webs and is only nodes and links; and a node browser diagrams and other computer-generated visible when one of those webs is active. To accesses an individual node in a hyper- images, video documentaries, and music. view documents with the links that belong document. Other browsers include attrib- Two courses, one on cell biology and one to a particular web, a user opens a web and ute browsers, version browsers, node on English literature, have been taught then opens one or more of its documents. differences bro wsers, and demon using the system. Current applications Although other webs may also reference browsers. (See Figure 9.) include InterText, a text processor; the document, only the links which were In Neptune, each end of a link has an InterDraw, a graphics editor; InterVal, a made in the current web are displayed. As offset within its node, whether that node time line editor that allows users interac- a 'result, the user does not have to sift is textual or graphical. * The link attach- tively to organize information in time and through the connections made in many ment may refer to a particular version of date sequences; InterSpec, a viewer for different contexts. a node, or it may refer to the current ver- sections of 3D objects; and InterPix, a The Intermedia project is also studying sion. The HAM provides two mechanisms scanned-image viewer. Under develop- ways of providing an effective browser for that are useful for building application ment are a video editor, a 2D animation a network that can include hundreds or layers: Nodes and links may have an editor, and more complex methods for even thousands of nodes. The Intermedia unlimited number of attribute/value pairs; filtering the corpus and creating and browser has two kinds of displays: a global and special high-speed predicates are traversing trails. map, which shows the entire hyperdocu- included for querying the values of these Intermedia is being developed both as a ment and allows navigation within it; and pairs in the entire hyperdocument, allow- tool for professors to organize and present a local map, which presents a view cen- their lesson material via computer and as tered on a single document and displaying an interactive medium for students to its links and nearest neighbors in the web. 'Unlikeinmosthypertextsystems,thedestinationend study the materials and add their own In addition, a display can show nodes and of a Neptunelinkisan iconicpoint in the textof the annotations and reports. links at several levels of detail. For exam- destination node rather than the whole node.

September 1987 29

Neptune Documents: Graph Browser

r by er Inte ac

Mu t me 10 conten

[KCBII6] Katz. R.H.• Chang. E. and Bhate!a. R. version modeling concepti for Multimedia content computer-aided design databases. I'roc. ileM SICMOD"6, (May 1986) 379-386. The name hypertext Is actually a misnomer for many of several systems,lndudlng Augment, )(anad~, N [Mey1l6] Mevrowltz. N. Intermedla: The Architecture and Construction of an Neptun~ and the Electronic Document Syste Object-OrIented Hypermedia System and Applications Frameworll. contents of a node to text. In general the contents of a rroc. ileM OOl'SLiI"6, (Noy 1986) 186-201. can be arbitrary digital data whose Interpretation may In or digitized speech. [Nellll~ Nelson. T.H. Literary Machines. T.H. Nelson, swarthmore, PA., 1981.

[RMNlIlJ Robertson, G., McCracken, D. and Newell, A. The ZOG approach to man-machine communication. '------1 International Journal of Man-Machine Studies, 14, 461-488, 1981.

Figure 9. Neptune browsers. Three browsers from Neptune are illustrated. A pictorial view of a network of nodes and links is shown in the Graph Browser (the upper window). The lower right window and the lower pane of the Document Browser are viewers for text nodes. Icons representing link attachments are shown embedded within the text in each of the nodes.

advantage of showing a natural hierarchy tigate more general hypertext design tions, which can be defined implicitly by of nodes: The windows of lower-level issues.!" Much of the interactive feel of a predicate (called an abstract collection) nodes are nested directly within their par- CREF reflects the style of use and pro- or explicitly by a list (called a static collec- ents. In most hypertext systems, no gramming of the Syrnbolics Lisp machine, lion). At any time, the selected collection attempt is made to display the parent-child on which it was built. Chunks of text, appears as a continuous length of text with relationship once the nodes are opened as called segments, constitute the nodes in the the segment boundaries marked by named windows. system. Segments are arranged in linear horizontal lines (such as "Segment 1," series, and can have keywords and various "Segment 2," etc.). This view can be Pitman's CREF. The Cross-Referenced kinds of links to other segments. The edited as if it were a single document. Editing Facility (CREF) is a prototype of notion of a linear set of segments is natu- One way of forming an abstract collec- a specialized text and graphics editor ral to the protocol analysis problem, since tion is by selecting segments using a which was developed originally as a tool the first step with such protocols is to seg- boolean predicate over keywords. To for use in analyzing the transcripts from ment them into the episodes of the exper- extend the power of this keyword facility. psychological experiments (known as pro- imental session. CREF allows the user to define a type hier- tocols), but which was also used to inves- CREF organizes segments into collec- archy on the keywords. For example, if

September 1987 31 a serial process and is, in any case, limited However, not all link traversals can be by the bandwidth of human linguistic instantaneous. Perhaps as important as processing. Spoken communication of rapid response is providing cues to the user parallel themes must mark items with about the possible delay that a given query stresses, pauses, and intonations which the than the nodes. The links form the "glue" or traversal might entail. For example, listener must remember as the speaker that holds the nodes together, but the some visual feature of the link icon could develops other lines of argument. Graphi- emphasis is on the contents of the nodes. indicate whether the destination node is in cal forms can use lists, figures, and tables From a computer science viewpoint, the memory, on the disk, somewhere else on to present ideas in a less than strictly lin- essence of hypertext is precisely that it is a the network, or archived off line. ear form. These visual props allow the hybrid that cuts across traditional bound- reader/viewer to monitor the items which aries.Hypertext is a database method, Properties of links. Links can be used he must understand together. One of the providing a novel way of directly access- for several functions. These include the challenges of good writing, especially good ing data. This method is quite different following: technical writing, is to present several par- from the traditional use of queries. At the • They can connect a document refer- allellines of a story or an argument in a same time, hypertext is a representation ence to the document itself. way that weaves them together coherently. scheme, a kind of semantic network which • They can connect a comment or anno- Traditional flat text binds us to writing mixes informal textual material with more tation to the text about which it is written. and reading paragraphs in a mostly linear formal and mechanized operation's and • They can provide organizational succession. There are tricks for signalling processes. Finally, hypertext is an interface information (for instance, establish the branching in the flow of thought when modality that features "control buttons" relationship between two pieces of text or necessary:Parenthetical comments, foot- (link icons) which can be arbitrarily between a table of contents entry and its notes, intersectional references (such as embedded within the content material by section). "see Chapter 4"), bibliographic refer- the user. These are not separate applica- • They can connect two successive ences, and sidebars all allow the author to tions of hypertext: They are metaphors for pieces of text, or a piece of text and all of say' 'here is a related thought, in case you a functionality that is an essential union of its immediate successors. are interested." There are also many rhe- all three. • They can connect entries in a table or torical devices for indicating that ideas figure to longer descriptions, or to other belong together as a set but are being The power of linking. In the next two tables or figures. presented in linear sequence. But these are sections of this article, I will explore links Links can have names and types. They rough tools at best, and often do not pro- and nodes in more detail as the basic build- can have a rich set of properties. Some sys- vide the degree of precision or the speed ing blocks of hypertext. tems allow the display of links to be turned and convenience of access that we would on and off (that is, removed from the dis- like. Linkfollowing. The most distinguishing play so that the document appears as ordi- Hypertext allows and even encourages characteristic of hypertext is its machine nary text). the writer to make such references, and support for the tracing of references. But The introduction of links into a text sys- allows the readers to make their own deci- what qualifies a particular reference- tem means that an additional set of sions about which links to follow and in tracing device as a link? How much effort mechanisms must be added for creating what order. In this sense, hypertext eases is permissible on the part of a user who is new links, deleting links, * changing link the restrictions on the thinker and writer. attempting to trace a reference? The names or attributes, listing links, etc. It does not force a strict decision about accepted lower limit of referencing sup- whether any given idea is either within the port can be specified as follows: To qualify Referential links. There are two flow of a paper's stream of thought or out- as hypertext, a system should require no methods for explicitly linking two points side of it. Hypertext also allows annota- more than a couple of keystrokes (or in hypertext-by reference and by organ- tions on a text to be saved separately from mouse movements) from the user to follow ization. The reference method is a non hi- the reference document, yet still be tightly a single link. In other words, the interface erarchical method. It uses referential links bound to the referent. In this sense, the must provide links which act like "magic that connect points or regions in the text. "linked-ness" of hypertext provides much buttons" to transport the user quickly and Referential links are the kind of link that of its power: It is the machine processible easily to a new place in the hyper- most clearly distinguishes hypertext. They document. links which extend the text beyond the sin- generally have two ends, and are usually gle dimension of linear flow. Another essential characteristic of directed, although most systems support At the same time, some applications hypertext is the speed with which the sys- "backward" movement along the link. demonstrate that the "node-ness" of tem responds to referencing requests. Only The origination of the link is called the hypertext is also very powerful. Particu- the briefest delay should occur (one or two "link source," and usually acts as the larly when hypertext is used as a thinking, seconds at most). Much design work goes reference. The source can logically be writing, or design tool, a natural cor- into this feature in most systems. One rea- either a single point or a region of text. At respondence can emerge between the son for this concern is that the reader often the other end, the "destination" of the link objects in the world and the nodes in the does not know if he wants to pursue a link usually functions as the referent, and can hypertext database. By taking advantage reference until he has had a cursory look of this object-oriented aspect, a hypertext at the referenced node. If making this 'Link deletion is problematical. For example, what user can build flexible networks which judgement takes too long, the user may should the policy be for nodes which are stranded when all their links have been deleted?Should they be model his problem (or solution). In this become frustrated and not bother with the placed in "node limbo" until the user decides what 10 application the links are less important hypertext links. do with them?

September 1987 33 from its neighboring material within the same node raises a tough implementation issue-how to display the selected region to the user. It must be highlighted some- how, using reverse video, fonts, or color, A but each of these options poses difficulties in keeping overlapping regions clearly Asl dlksjdf dkf sl 4elsldfj aslkdfj sljsad asdlkfj;l fjslkja a\;kjd jl highlighted. The Intermedia designers pro- slkjv erwoiwnmm em, uink1l-_-~~_ pose to draw a light box around regions Indm dsotuewr, djld' w, Y and a darker box around region/region kjdf d'\ owmd. On nv vn sdlfkj xxxx jl dlew vio nvi overlaps, thus showing a single level of sve vkins ; vkluv cvoiew , m k oi ovcrlapping'<; however, this technique is ionolf f1kd. not effective if there are more than two SOY vi voinsek voierwd. vienm overlapping regions. aio vimns ivds li vinoern vi dinv wor glkr lt l reiubc rcbier uvrcbx Another difficulty posed by link regions rhkrkb "lkdslksd djnvuin" dfoi is how to show the name ofthe link. Unlike sew cv ebnwe iubvi cvubw viu iuhsdibn denewin niouc dsiub d a link point, a link region has no obvious indsi iousk dk ds iuwi. _- •..••••.•"------••••.• position for a title, unless it is placed arbitrarily at the beginning or end of the B region. Bgh sdkj dlkjs kewoj vodiu od soi Link regions can also be difficult to slke id sdoi aionsl dsiunfl soi dis oi s soijsdi sdoijsd oids dios oi dsoi manipulate. Designers must devise a sys- sdoi sdois sdoids dsoijsd doi dsoids tem for copying, moving, modifying, and s II oiosdj ewos sdoie dioiewnzxon osidoiw soidn. deleting the region and the substrings within it. The movement of regions Ywe we d eoid soinvcoiz zxoid di sdoia asoinv aoidsna oianaois dnoi involves logistical dilemmas which are not soandoia a aoinds said aid odno easy to resolve: For example, when one soia aoidnaoinao 0 oisdo dcloind aoinal. moves a major portion of the text in a destination region to someplace else in the node, should the link destination move with it or stay with what remains? Also, designers must make special provisions for Figure 10. An example of a link with a point source and a region destination. The deleting, moving, or copying the defining source of the link is a token in the text of document A which contains a textual end points of a region. identifier ("xxxx"). The identifier may be (1) the name of the destination node (in this case it would be "B"), (2) the name of the link, or (3) an arbitrary string which Organizational links. Like reference is neither the name of the link nor the destination node. The destination of this link links, organizational links establish is node B which is a region. The link has an internal name (5327) which is normally explicit links between points in hypertext. visible to the user. Organizational links differ from referen- tiallinks in that they implement hierarchical information. Organizational links connect a parent node with its children and thus form a strict tree subgraph within the hypertext network graph. They correspond to the [S- also be either a point or a region. (See Fig- ure 10 illustrates the most common form A (or superconcept) links of semantic net ure 10.) of hypertext link, in which the source is a theory, and thus operate quite differently A link point is some icon indicating the point and the destination is a region. This than referential links. * For example, presence of the link. It usually shows the example typifies many of the link applica- rather than appearing as explicit high- link's name and perhaps also its type. Or tions listed above, because it shows how a lighted tokens in each node, organiza- it may show the name and/or type of the chunk of text-a region-is written about tional links are often traversed by a destination node. In systems such as Nep- or referenced by some smaller chunk of separate mechanism at the node control tune which support links with both point text, often a sentence. Since most readers level (i.e., special go to-parent , goto-first- source and point destination, the icon also are accustomed to single point references child, and goto-next-sibling commands). indicates which type of link is indicated. In to sentences (i.e., footnotes), they have no In other cases, there are organizational some systems, the display of links can be problem accepting a link with a point nodes (such as toc nodes in Tcxtnet and suppressed, so that the documents appear source. There can be regions in graphics as File Boxes in NoteCards) which record the linear. well-either bordered regions or collec- organizational structure. A link region is a set of contiguous tions of graphic objects in a figure. Link regions can pose difficult design *Note that organizational links are distinct from the characters which is displayed as a single class hierarchy links that would be used (in the object- unit. In Figure 10, the link destination is problems. They are easiest to implement oriented programming paradigm) to define types and a link region, namely, an entire node. Fig- as whole nodes, since setting a region off subtypes of nodes in the hypertext system.

34 COMPUTER Keyword links. In addition to the several ways. Links can connect more than explicit linking performed by referential two nodes to form cluster links. Such clus- and organizational links, there is a kind of ter links can be useful for referring to implicit linking that occurs through the use several annotations with a single link, and of keywords. This type of linking is yet to for providing specialized organizational be fully explored. (73 percent) of which connected FileBoxes structures among nodes. Indeed, the toe One of the chief advantages of text stor- to each other or to individual notecards, nodes of Textnet and the FileBoxes of age on a computer is the ability to search 261 (7.5 percent) of which were nonhier- NoteCards are both forms of cluster links. large and complex documents and sets of archical referential links, and the One useful way to extend the basic link documents for substrings and key- remainder of which were mail links (used is to place attribute/value pairs on links words. * Naturally, this ability is also a by the system to tie mail messages to other and to query the network for them. The valuable aspect of hypertext. Indeed, most nodes). This example, for what it is worth, Neptune system, for example, has an users of large hyperdocuments insist on suggests that hierarchical structure is very architecture that is optimized for this func- having some mechanism for scanning their important in organizing a hypertext net- tion. Coupled with specialized routines in content, either for selected keywords work, and that referential links are impor- the database interpreter (the HAM), these (which can apply to nodes, links, or tant but less common. attribute lists allow users to customize regions) or for arbitrary embedded strings. One advantage of a strictly tree-oriented links in several ways, including devising From a functional standpoint, link fol- system is that the command language for their own type system for links and per- lowing and search are similar: Each is a navigation is very simple: From any node, forming high-speed queries on the types. way to access destination nodes that are of the most one can do is go to the parent, a It is also possible to perform procedural possible interest. Link following usually sibling, or a child. This simplicity also attachments on a link so that traversing the yields a single node, whereas search can diminishes the disorientation problem, link also performs some user-specified side yield many; hence, a keyword is a kind of since a simpler cognitive model of the effect, such as customizing the appearance implicit computed link. The value of this information space will suffice. of the destination node. This ability is insight is that it may allow design of a Of course, the great disadvantage of any provided in Neptune and Boxer. hypertext interface which is consistent hierarchy is that its structure is a function across all link-tracing activities. of the few specific criteria that were used Hypertext nodes. Although the essence in creating it. For example, if one wishes of hypertext is its machine-supported link- To tree or not to tree. Some hypertext to investigate what sea-based life forms ing, the nodes contribute significantly to systems (for example,Emacs INFO) sup- have in common with land-based life defining the operations that a hypertext port only hierarchical structures, others forms, one may find that the traditional system can perform.Most users of hyper- (such as Xanadu and Hyperties) provide classification of life forms into the plant text favor using nodes which express a sin- no specific support for hierarchical struc- and animal kingdoms breaks up the infor- gle concept or idea, and are thus much tures, and others (such as Textnet and mation in the wrong way. The creator of smaller than traditional files. When nodes NoteCards) support both kinds of a hierarchical organization must anticipate are used in this fashion, hypertext structures. the most important criteria for later access introduces an intermediate level of One could question just how sufficient to the information. One solution to this machine support between characters and strictly hierarchical structures are, and for dilemma is to allow the information ele- files, a level which has the vaguely seman- which applications they are sufficient and ments to be structured into multiple hier- tic aspect of being oriented to the expres- for which they are not. On the one hand, archies, thus allowing the world to be sion of ideas. But this sizing is completely abstraction is a fundamental cognitive "sliced up" into several orthogonal at the discretion of the hypertext writer, process, and hierarchical structures are the decompositions. Any hypertext system and the process of determining how to most natural structures for organizing which has hierarchy nodes, such as Text- modularize a document into nodes is an levels of abstraction. On the other hand, net (toe nodes) and NoteCards (FileBox art, because its impact on the reader is not cases obviously exist where cross- nodes), can perform this operation quite well understood." hierarchical links are required. Frank easily. These are the only systems which Halasz, one of the developers of explicitly claim to support multiple hierar- The modularization of ideas. Hypertext NoteCards, has gathered statistics on the chies. Indeed, one early user of NoteCards invites the writer to modularize ideas into hyperspace of a single representative used the system in doing the research and units in a way that allows (1) an individual NoteCards user; this person had 1577 writing for a major project paper; he idea to be referenced elsewhere, and (2) nodes (cards) in all, 502of which were File- imposed one organization on the data and alternative successors of a unit to be Boxes (hierarchical nodes). Connecting his writings while doing the research, and offered to the reader (for instance, more these nodes were a total of 3460links, 2521 then quite a different (yet coexistent) detail, an example, bibliographic refer- organization on the same material to pro- ences, or the logical successor). But the duce his paper. As a generalization, it "There is some controversy over the relative merits of writer must also reckon with the fact that keyword retrieval as onnoseno full text search. On the seems that engineering-oriented hypertext a hypertext node, unlike a textual para- one hand. keyword retrieval is only asgood asthe skill users prefer hierarchical organizations, graph, tends to be a strict unit which does and thoroughness of the person selecting the key- whereas arts- or humanities-oriented users words. On the other hand, full text search does not not blend seamlessly with its neighbors. find all the relevant documents, nor does it always find prefer cross-referencing organizations. Some hypertext systems (Notecards, only the relevant documents. Its shortcomings are due CREF, Boxer,FRES, NLS) allow nodes to in part to the commonness of synonyms in English. In addition, full text search can be computationally pro- Extensions to basic links. Certain fea- be viewed together as if they were one big hibitive in large networks. tures of the link enable it to be extended in node, and this option is essential for some

September 1987 35 applications (for example, wntmg and Semistructured Nodes. So far I have reading prose). But the boundaries around spoken of the hypertext node as a struc- nodes are always discrete and require tureless "blank slate" into which one sometimes difficult judgements about how might put a word or a whole document. to cleave the subject matter into suitable ment hierarchically (i.e., as an outline) at For some applications, there is growing chunks. the same time that one adds new sections interest in semistructured nodes-typed The process of identifying a semanti- and embellishes existing ones. People nodes which contain labelled fields and cally based unit, such as an idea or con- don't think in terms of "screenfulls"; they spaces for field values. The purpose of cept, with a syntactic unit, such as a think in terms of ideas, facts, and evi- providing a template for node contents is paragraph or hypertext node, is not unique dence. Hypertext, via the notion of nodes to assist the user in being complete and to to hypertext. Manuals of style notwith- as individual expressions of ideas, provides assist the computer in processing the standing, traditional text has rather loose a vehicle which respects this way of think- nodes. The less that the content of a node conventions for modularizing text into ing and working. is undifferentiated natural language (for paragraphs. This looseness is acceptable example, English) text, the more likely that because paragraph boundaries have a rela- Typed nodes. Some hypertext systems the computer can do some kinds of limited tively minor effect on the flow of the read- sort nodes into different types. These processing and inference on the textual ing. Paragraph boundaries are sometimes typed nodes can be extremely useful, par- subchunks, This notion is closely related provided just to break up the text and give ticularly if one is considering giving them to Malone's notion of semistructured the eye a reference point. Thus, decisions some internal structure, since the types can information systems." about the distribution of sentences among be used to differentiate the various struc- To continue with the example of the paragraphs is not always critical. tural forms. Design Journal, we have developed a Hypertext, on the other hand, can For example, in our research in the model for the internal structure of deci- enforce a rather stern information hiding. MCC Software Technology Program, we sions. The model is named ISAAC. It In some systems, the only clue a user has have been implementing a hypertext inter- assumes that there are four major compo- as to the contents of a destination node is face for a design environment called the nents to a design decision: the name of the link (or the name of the Design Journal. The Design Journal is (I) an issue, including a short name node, if that is provided instead). The intended to provide an active scratch pad for the issue and a short paragraph writer is no longer making all the decisions in which the designer can deliberate about describing it in general terms; design decisions and rationale, both about the flow of the text. The reader can (2) a set of alternatives, each of which and must constantly decide which links to individually and in on-line design meet- resolves the issue in a different way, pursue. In this sense, hypertext imposes on ings, and in which he can integrate the each having a name and short design itself with this less formal kind of both the writer and the reader the need for description, and each potentially information. For this purpose we have more process awareness, since either one linked to the design documents or ele- has the option of branching in the flow of provided a set of four typed nodes for the ments that implement the alternative; the text. Thus hypertext is best suited for designer to use-notes, goals/constraints, (3) an analysis of the competing alter- applications which require these kinds of artifacts, and decisions. Notes are used for natives, including the specific criteria judgements anyway, and hypertext merely everything from reminders, such as "Ask being used to evaluate them, the offers a way to act directly on these judge- Bill for advice on Module X," to specific trade-off analysis among these alter- ments and see the results quickly and problems and ideas relating to the design. natives, and links to any data that the graphically. Goals/ constraints are for the initial analysis draws upon; and requirements as well as discovered con- (4) a commitment to one of the alter- Ideas as objects. While difficult to docu- straints within the design. Artifacts are for natives (however tentatively) or to a ment, there is something very compelling the elements of the output: The Design. vector of preferences over the alter- about reifying the expression of ideas into And decisions are for capturing the branch natives, and a subjective rating about discrete objects to be linked, moved, and points in the design process, the alterna- the correctness or confidence of this changed as independent entities. Alan Kay tives considered by the designer, and some commitment. and Adele Goldberg+' observed of of the rationale for any commitment (how- Smalltalk that it is able to give objects a ever tentative) that has been made. The Without getting into the details of the perceptual dimension by allocating to designer captures assumptions in the form underlying theory, I merely wish to stress them a rectangular piece of screen real of decisions with only one alternative. Our here that the internal structure of ISAAC estate. This feature offers enhanced prototype of the Design Journal uses color suggests that the author of an ISAAC deci- retrieval and recognition over computer- to distinguish between note types in the sion is engaged in a much more structured processed flat documents, because to a browser, and we have found this to be a activity than just' 'writing down the deci- much greater degree abstract objects are very effective interface. sion," and the reader is likewise guided by directly associated with perceptual Hypertext systems that use typed nodes the regularity of the ISAAC structure. objects-the windows and icons on the generally provide a specialized color, size, Of course, it may not be clear why we do screen. or iconic form for each node type. The dis- not treat each of the elements listed above Paragraphs, sections, and chapters in a tinguishing features help the user di fferen- as its own typed hypertext node. The rea- book, viewed through a standard text edi- tiate at a glance the broad classes of typed son is that the parts of an ISAAC frame tor or word processor, don't stand out as nodes that he is working with. Systems are much more tightly bound together first-class entities. This is particularly such as NoteCards, Intermedia, and IBIS than ISAAC frames are bound to each apparent when one canview one's docu- make extensive use of typed nodes. other. For example, we could not have an

36 COMPUTER analysis part without an alternatives part; importance of hypertext is simply that yet if we treat them as separate hypertext references are machine-supported. Like nodes, we have failed to build this con- hypertext, traditional literature is richly straint into the structure. The general issue interlinked and is hierarchically organized. here is that some information elements One problem with composite nodes is In traditional literature, the medium of must always occur together, while others that as the member nodes grow and change print for the most part restricts the flow of may occur together or not, depending on the aggregation can become misleading or reading to follow the flow of linearly how related they are in a given context and incorrect. A user who encounters this arranged passages. However, the process how important it is to present them as a problem is in the same predicament as a of following side links is fundamental even cluster distinct from "surrounding" infor- writer who has rewritten a section of a in the medium of print. In fact, library and mation elements. This problem is recur- paper so thoroughly that the section title information science consist principally of sive; An element that is atomic at one level is no longer accurate. This "semantic the investigation of side links. Anyone may turn out on closer inspection to con- drift" can be difficult to catch. who has done research knows that a contain many components, some of which are siderable portion of that effort lies in clustered together. Analogy to semantic networks. The idea obtaining referenced works, looking up In hypertext this tension presents itself of building a directed graph of informal cross-references, looking up terms in a dic- as the twin notions of semistructured textual elements is similar to the AI con- tionary or glossary, checking tables and nodes and composite nodes. cept of semantic networks. A semantic figures, and making notes on notecards. Composite nodes. Another mechanism network is a knowledge representation Even in simple reading one is constantly for aggregating related information in scheme consisting of a directed graph in negotiating references to other chapters or hypertext is the composite node. Several which concepts are represented as nodes, sections (via the table of contents or refer- related hypertext nodes are "glued" and the relationships between concepts are ences embedded in the text), index entries, together and the collection is treated as a represented as the links between them. footnotes, bibliographic references, side- single node, with its own name, types, ver- What distinguishes a semantic network as bars, figures, and tables. Often a text sions, etc. Composite nodes are most use- an AI representation scheme is that con- invites the reader to skip a section if he is ful for situations in which the separate cepts in the representation are indexed by not interested in greater technical detail. their semantic content rather than by some items in a bulleted list or the entries in a But there are problems with the traditional methods. table are distinct nodes but also cohere into arbitrary (for example, alphabetical) a higher level structure (such as the list or ordering. One benefit of semantic net- • Most references can't be traced back- table). This practice can, however, under- works is that they are natural to use, since wards: A reader can not easily find where mine the fundamental association of one related concepts tend to cluster together in a specific book or article is referenced in interface object (window) per database the network.Similarly, an incompletely or a document, nor can the author of a paper object (node), and thus must be managed inconsistently defined concept is easy to find out who has referenced the paper. well to avoid complicating the hypertext spot since a meaningful context is provided • As the reader winds his way down var- idiom unduly. by those neighboring concepts to which it ious reference trails, he must keep track of A composite node facility allows a is already linked. which documents he has visited and which group of nodes to be treated as a single The analogy to hypertext is straightfor- he is done with. node. The composite node can be moved ward: Hypertext nodes can be thought of • The reader must squeeze annotations and resized, and closes up to a suitable icon as representing single concepts or ideas, into the margins or place them in a sepa- reflecting its contents. The subnodes are internode links as representing the seman- rate document. separable and rearrangeable through a tic interdependencies among these ideas, • Finally, following a referential trail subedit mode. The most flexible means of and the process of building a hypertext net- among paper documents requires substan- displaying a composite node is to use a work as a kind of informal knowledge tial physical effort and delays, even if the constraint language (such as that devel- engineering. The difference is that AI reader is working at a well-stocked library. oped by Symbolics for Constraint Frames) knowledge engineers are usually striving to If the documents are on line, the job iseas- which describes the sub nodes as panes in build representations which can be ier and faster, but no less tedious. the composite node window and speci fies mechanically interpreted, whereas the goal the interpane relationships as dynamic of the hypertext writer is often to capture New possibilities for authoring and design. constraints on size and configuration. an interwoven collection of ideas without Hypertext may offer new ways for authors Composite nodes can be an effective regard to their machine interpretability. and designers to work. Authoring is means of managing the problem of having The work on semantic networks also sug- usually viewed as a word- and sentence- a large number of named objects in one's gests some natural extensions to hypertext, level activity.Clearly the word processor * environment. Pitman described the prob- such as typed nodes, semistructured nodes (frames), and inheritance hierarchies of 'Actually, the term "word processor" is quite mis- lem this way: node and link types. leading. Most such tools accept input only at the In this sort of system, there is a never-ending character level, and manipulate characters, words, tension between trying to name everyttung (in semences, and parllsraphs with equal facility. So these which case, the number of named things can tools manipulate units of text, not words. But do they grow quickly and the set can become quickly "process" these units? "Processing" implies that the computer performs some additional work, such as unmanageable) or to name as little as possi- The advantages and changing the verb form if the subject was changed ble (in which case, things that took a lot of uses of hypertext from singular to plural, or performing real-rime spell- trouble to construct can be hard to retrieve ing and grammar correction. Since this is not the case, if one accidentally drops the pointers to we really should return to the original term for these them)." Intertextual references are not new. The 1001s: "text editors".

September 1987 37

File Edit Ulew font Rrrnngement Rlign Ooto ( ustcmtze

IIsh/ConteHt32.304.1BO: Global Map

Figure 11. Tangled web of links. This experimental implementation of a global map in the Interrnedia system shows the difficulty of providing users with spatial cues once a linked corpus contains more than a few dozen documents. This global map only represents about one tenth of the documents in a corpus designed for a survey of English literature course.

properties useful in visual differentiation large hyperdocument, one is by definition standard database search and query tech- (color, size, shape, texture), and maintain- disoriented. In addition, an adequate vir- niques to locating the node or nodes which ing certain similarities to our physical envi- tuality is very difficult to maintain for a the user is seeking.This is usually done by ronment (for example, no two objects large or complex hypertext network. Such using boolean operations to apply some occupy the same space, things only move parameters as (1) large numbers of nodes, combination of keyword search, full string if moved, etc.), browser designers are able (2) large numbers of links, (3) frequent search, and logical predicates on other to create quite viable virtual spatial envi- changes in the network, (4) slow or awk- attributes (such as author, time of crea- ronments. Users orient themselves by vis- ward response to user control inputs, (5) tion, type, etc.) of nodes or links. Simi- ual cues, just as when they are walking or insufficient visual differentiation among larly, one can filter (or el/ide) information driving through a familiar city. However, nodes and/or links, and (6) non visually so that the user is presented with a manage- there is no natU'ral topology for an infor- oriented users combine to make it practi- able level of complexity and detail, and can mation space, except perhaps that higher cally impossible to abolish the disorienta- shift the view or the detail suppression level concepts go at the top or on the left tion problem with a browser alone. while navigating through the network. side, so until one is familiar with a given One solution to this dilemma is to apply However, much research remains to be

September 1987 39

Intellect," in Vistas in Information Han- 20. P.J. Brown, "Interactive Documentation," dling, vol. I, Spartan Books, London, in Software: Practice and Experi- 1963. ence, March 1986, pp. 291-299. 4. D.C. Engelbart and W.K. English, "A 21. D. Shasha, "When Does Non-Linear Text Research Center for Augmenting Human Help? Expert Database Systems, Proc. of Intellect," AFlPS Conf. Proc., vol. 33, the Firs!Int'! Conf., April 1986, pp. Pari I, The Thompson Book Company, 109-121. Washington, D.C., 1968. 22. A. Kay and A. Goldberg, "Personal 5. T.H. Nelson, "Replacing the Printed Dynamic Media," Computer, March 1977, Word: A Complete Literary System, " IFIP pp.31-41. Proc., October 1980, pp. 1013-1023. E. Jeffrey Conklin is a member of the research 23. T.W. Malone et al, "Intelligent staff and GE's liaison to the Software Technol- 6. R.H. Trigg, A Network-basedApproach to Information-Sharing Systems," Communi- ogy Program in the Microelectronics and Com- Text Handling for the Online Scientific cations of the ACM, May 1987, pp. puter Technology Corporation (MCC). His Community, PhD. Thesis, University of 390-402. research centers on constructing information Maryland, 1983. 24. W .Gibson, Neuromancer, Ace Science Fic- systems for the capture and use of design 7. H. Rittel and M. Webber, "Dilemmas in a tion, 1984. rationale. General Theory of Planning," Policy Conklin Received his BA from Antioch Col- Sciences, Yol. 4,1973. A more detailed version of this article, lege and his MS and PhD from the University 8. D.G.Lowe, "Cooperative Structuring of including an extended bibliography, is avail- of Massachusetts at Amherst. Information: The Representation of able from the author. To obtain a copy, cir- Reasoning and Debate," in Int'l. 1. of Man- cle number 181 on the Reader Service Card Readers may write to Conklin at MCC Soft- Machine Studies," Yol. 23, 1985, pp. at the back of the magazine. ware Technology Program,P.O. Box 200195, 97-111. Austin, TX 78720; (512) 343-0978. 9. 1.B Smith et ai, "WE: A Writing Environ- ment for Professionals," Technical Report Copyright © 1987 The Institute of Electrical and Electronics Engineers, Inc. 86-025, Department of Computer Science, Reprinted with permission from COMPUTER, University of North Carolina at Chapel 10662 Los Vaqueros Circle,Los Alamitos, CA 90720 Hill, August 1986. 10. W. Hershey, "Idea Processors," BYTE, June 1985, p. 337. II. D. McCracken and R.M. Akscyn, "Expe- rience with the ZOG Human-computer Interface System," Int'l J. of Man-Machine Studies, Yol. 21,1984, pp. 293-310. 12. B.Sbneiderman and J. Morariu, "The Interactive Ency-clopedia System (TIES)," Department of Computer Science, Univer- sity of Maryland, College Park, MD 20742, June 1986. 13. J.H. Walker,"The Document Examiner," SIGCRAPH VideoReview, Edited Compi- lation from CH1'85: Human Factors in Computing System, 1985. 14. F.G. Halasz, T.P. Moran,andT.H. Trigg, "NoteCards in a Nutshell," Proc. of the ACM Conf on Human FactorsinComput- ingSystems, Toronto, Canada, April 1987. 15. N.L. Garrett, K.E. Smith, and N.Mey- rowhz, "Intermedia: Issues,Strategies, and Tactics in the Design of a Hypermedia Document System," in Proc. Conf. on Computer-Supported Cooperative Work, MCC Software Technology Program, Aus- tin, Texas, 1986. 16. N. Yankelovich,N. Meyrowitz, and A. van Dam, "Reading and Writing the Elec- tronic Book," Computer, October 1985. 17. N. Delisle and M. Schwartz, "Neptune:A Hypertext System for CAD Applications," Proc. of ACM SIGMOD Int'l Conf. on Management of Data, Washington, D.C., May 28-30, 1986, pp. 132-143. (Also available as SIGMOD Record Yol. 15, No.2, June 1986). 18. A. diSessa, "A Principled Design for an Integrated Computational Environment," Human-Computer Interaction, Vol.I, Lawrence Erlbaum, 1985, pp. 1-47. 19. K.M.Pitman, "CREf: An Editing facility for Managing Structured Text," A.I. Memo No. 829, M.I.T. A.I. Laboratory, Cambridge, Mass.,February 1985.

September 1987