JOHN B. SMITH and STEPHEN F. WEISS
`Guest Editors
`
`This special issue is devoted to a form of electronic
`is
`document called hypertext. More precisely, hypertext
`an approach to information management in which data
`is stored in a network of nodes connected by links.
`Nodes can contain text, graphics, audio, video, as well
`as source code or other forms of data. The nodes, and in
`some systems the network itself, are meant to be
`viewed through an interactive browser and manipu-
`lated through a structure editor.
`While the term, hypertext, was coined by Ted Nelson
`during the 1960s [5], the concept can be traced to Van-
`nevar Bush’s 1945 description of “the memex”:
`A. device in which an individual stores his books,
`records, and communications, and which is mecha-
`nized so that it may be consulted with exceeding
`speed and flexibility.
`It is an enlarged intimate sup-
`plement to his memory [I].
`
`What distinguished Bush’s concept from other forms of
`data storage was its associative structure that closely
`modeled the structure of human memory:
`The human mind . . . 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.
`
`0 7988 ACM OOOI-0782/88/0700-0816
`
`$1.50
`
`Selection by association, rather than indexing,
`may yet be mechanized. One cannot hope . . . to
`equal the speed and flexibility with which the
`mind follows an associative trail, but it shmould be
`possible to beat the mind decisively in regard to
`the permanence and clarity of the items resur-
`rected from storage.
`
`The first serious attempt to build a memex did not
`take place until 20 years after Bush’s description. In
`1968, Doug Engelbart, then at Stanford Research Insti-
`tute, conducted a dramatic live demonstration of his
`Augment system at the Fall Joint Computer (Conference
`in which he worked collaboratively on a hypertext doc-
`ument with a colleague 500 miles away [4]. .During that
`session, Engelbart also demonstrated two of bis other
`inventions-the mouse and the chord key set.
`In the 20 years since Engelbart’s demonstration, both
`interest and activity
`in hypertext have grown steadily.
`Jeff Conklin’s excellent survey traces this history in
`detail [2]. Some of the more important milestones in-
`clude the following:
`
`ZOG, a high-performance system developed at Carne-
`gie-Mellon University and used aboard the USS Carl
`Vinson. ZOG is the predecessor of KMS, a commercial
`system described in the article by Robert Akscyn,
`Donald McCracken and Elise Yoder that begins on
`page 820.
`
`616
`
`Commumications of the ACM
`
`July 1988 Volume 31 Number 7
`
`Facebook's Exhibit No. 1020
`Page 1
`
`

`

`l
`
`and several earlier systems, developed by
`Intermedia,
`a research group at Brown University
`that traces its
`ancestry
`to Nelson
`[8].
`l NoteCards,
`the most ambitious system of the past
`decade, developed at Xerox PARC. NoteCards
`is de-
`scribed
`in detail
`in the article by Frank Halasz begin-
`ning on page 836.
`engineered high-
`a beautifully
`l Document Examiner,
`that provides on-
`performance
`system by Symbolics
`line access to their user documentation
`[7].
`l Neptune, a hypertext
`system for computer assisted
`software engineering,
`developed at Tektronix
`[3].
`l WE, a hypertext
`authoring system developed at the
`University
`of North Carolina
`that produces conven-
`tional paper as well as electronic documents and
`closely models human cognitive processes
`[6].
`
`has accel-
`in hypertext
`the past year interest
`During
`erated sharply. No one factor explains
`it. More power-
`ful workstations,
`high-resolution
`graphic displays,
`in-
`creased network communications,
`and decreased costs
`for large on-line storage all contributed.
`Two specific events, however, seem to have played a
`particularly
`strong role. The first event was Apple’s
`in-
`troduction of HyperCard. While
`this system is relatively
`primitive
`compared with some earlier ones, Apple’s ag-
`gressive promotion of it is changing hypertext
`from an
`esoteric concept known
`to a few hundred people
`to a
`household staple of computing being used by millions.
`The second event was Hypertext
`‘87, the first major
`conference devoted entirely
`to hypertext. This work-
`shop brought
`together an extremely
`broad spectrum of
`people.
`It drew participants
`from five continents. The
`meeting
`included computer scientists
`from a number of
`different areas, among them information
`retrieval,
`text
`and image handling, software engineering, VLSI design,
`graphics, and human-computer
`interaction. Academics
`came from a number of additional
`disciplines,
`includ-
`ing classics, philosophy,
`psychology, English,
`foreign
`languages,
`religious studies, and medicine. A number of
`commercial
`interests were also represented,
`including
`system developers, on-line
`information
`vendors, and
`people planning
`to develop hypertext
`databases
`in spe-
`cific subject areas. And there were the users, those
`wanting
`to use hypertext
`to deliver medical
`informa-
`tion, train writers, and manage software development.
`This meeting of individuals
`from such a broad spec-
`trum of backgrounds and interests has generated con-
`siderable momentum
`that is appearing
`in many differ-
`ent forms: hypertext meetings
`in specialized areas, new
`commercial
`ventures such as hypertext
`publishing
`companies, and a number of publications
`on the topic,
`including
`this special
`issue.
`such at-
`is attracting
`To understand why hypertext
`“docu-
`tention, one must understand how a hypertext
`ment” differs
`from a conventional
`paper document.
`In most conventional
`paper documents-such
`as
`journal articles, specifications,
`or novels-physical
`structure and logical structure are closely related. Phys-
`ically,
`the document
`is a long linear sequence of words
`
`into lines and pages for conven-
`that has been divided
`ience. Logically,
`the document
`is also linear: words are
`combined
`to form sentences, sentences
`to form para-
`graphs, paragraphs
`to form sections, etc. If the docu-
`ment has a hierarchical
`logical structure, as do many
`expository documents such as journal articles,
`that hi-
`erarchy
`is presented
`linearly:
`the abstract or overview
`of the whole comes first, followed by the introduction,
`the first section,
`the second section, etc., until
`the con-
`clusion. This linearity
`is easy to see if one imagines
`the
`hierarchical
`structure
`represented as an outline, with
`the sections of the document appearing
`in the same
`order as they normally do in the outline. Such docu-
`ments strongly encourage
`readers
`to read them linearly,
`from beginning
`to end following
`the same sequence.
`A few conventional
`paper documents-such
`as ency-
`clopedias, dictionaries,
`and other reference works-
`separate
`logical structure
`from physical structure. Phys-
`ically,
`these documents are linear sequences of inde-
`pendent units, such as articles on specific
`topics or en-
`tries for individual words. Logically,
`they are more
`complex. The reader seldom reads such documents
`from beginning
`to end, but rather searches them to
`
`Hypertext electronic documents provide
`most of the flexibility of reference works as
`well as add a number of new features.
`
`(a form of random
`locate the article or entry of interest
`access), and then reads that portion sequentially. How-
`ever, the reader
`is likely
`to encounter various cross
`references
`to other entries while
`reading as well as a
`list of “see also’s” at the end of an article. To follow
`those pointers,
`the reader must locate the appropriate
`volume,
`find the appropriate
`entry, and then the rele-
`vant portion. The logical structure of reference and
`other similar documents
`is, thus, more complex. They
`have a sequential structure
`that aids search, but the
`logical path of the reader
`is a network
`that can criss-
`cross the entire document or set of documents,
`from
`one item to another,
`to another, etc. Such documents
`are more flexible but they are also cumbersome, partic-
`ularly when
`they appear
`in large, multivolume
`formats.
`Hypertext
`electronic documents provide most of the
`flexibility
`of reference works as well as add a number
`of new features. Earlier, we described a hypertext
`as a
`document
`in which
`information
`is stored in nodes con-
`nected by links. Each node can be thought of as analo-
`gous to a short section of an encyclopedia
`article or
`perhaps a graphic
`image with a brief explanation.
`The
`links
`join these sections
`to one another
`to form the
`article as a whole and the articles
`to form the encyclo-
`pedia. These links are usually shown
`for each node as a
`“from”
`link pointing
`to the node just read and a set of
`“to” links
`that indicate
`the (usual) multiple nodes
`which one may select to read next.
`
`]uly 1988 Volume 31 Number 7
`
`Communications of the ACM
`
`Facebook's Exhibit No. 1020
`Page 2
`
`

`

`; SPECIAL
`ISSUE
`
`u
`
`Many systems also include pointers embedded in the
`text iiself that link a specific portion to some other
`node or portion of text. Thus, one moves from node to
`node by selecting the desired “to” link, an embedded
`cross-reference link, or the “from” link to return to the
`previous node. For many documents, the “to” links can
`be thought of as organizational. Collectively,
`they fre-
`quently form a hierarchical structure analogous to the
`hierarchical
`logical structure of many conventional
`documents. From this perspective, the embedded,
`cross-reference links cross the main organizational
`structure.
`While we can establish a rough analogy between the
`two, h.ypertext documents are much more flexible
`than
`conventional documents. For example, one can read
`the hypertext article just as one reads the conventional
`paper article by first reading the overview node, then
`the first section node(s), the second section, etc. How-
`
`While conventional publications are
`limited
`to text and graphics, hypertext
`nodes offer sound, video sequences,
`animation, even comauter vro~rams that
`begin run&q when ;he nddes”in which
`they are stored are selected.
`
`m
`
`ever, one can also read the sections in different orders.
`For example, if the hierarchical structure of the article
`is viewed as a two-dimensional
`tree or organization
`chart instead of as a linear outline, one can easily imag-
`ine that if the “to” links were shown as the children of
`the current node, selecting the second section before
`the first or perhaps skipping the first entirely. Hyper-
`text documents are also much more convenient. To
`follow the cross-references in a modern encyclopedia
`often means moving among thirty of more (heavy) vol-
`umes. Readers do it, but it is a slow, frequently
`labori-
`ous, task.
`While hypertext provides greater flexibility and con-
`venience than conventional documents, its power and
`appeal increase dramatically when it is implemented in
`computing environments
`that include networked mi-
`crocomputers and workstations, high-resolution dis-
`plays, and large on-line storage. While following a
`cross-reference in a 88-volume encyclopedia can take
`several minutes, many hypertext systems can deliver
`the next node in less than a second and from a much
`larger body of information
`that might take thousands of
`volumes in print. While conventional publications are
`limited to text and graphics, hypertext nodes offer
`sound, video sequences, animation, even computer pro-
`grams that begin running when the nodes in which
`they a.re stored are selected. While the organizational
`and cross-reference structures of conventional docu-
`ments are fixed at the time of printing, hypertext
`links
`and nodes can be changed dynamically.
`Information
`in
`
`We hope the reader, beginning with a
`narrower but deeper understanding of
`hypertext, will be well prepared to read
`further
`in the literature, consider using
`hypertext for a specific application, or
`think about the many issues raised by this
`technology.
`
`individual nodes can be updated, new nodes can be
`linked into the overall hypertext structure, and new
`links added to show new relationships. In some sys-
`tems, users can add their own links to form new organi-
`zational structures, creating new documents from old.
`Each of these changes represents an incremental dif-
`ference between hypertext and conventional docu-
`ments, but when considered together, they are produc-
`ing a qualitative change in the way some people are
`conceptualizing
`information
`resources. It is this shift in
`perspective that is creating such excitement and such a
`wealth of new possibilities in the minds of some. This
`special issue was assembled with the goal of providing
`readers unfamiliar with hypertext with sufficient
`infor-
`mation so that they can see the potential for hypertext
`in their own fields and, perhaps, share this intellectual
`ferment.
`The six articles included in this special issue were all
`presented at Hypertext
`‘87 held at the University of
`North Carolina at Chapel Hill last November. In select-
`ing them, we have not attempted to give an overview of
`work in the field-again, we refer the reader to [Z] for
`this. Instead, we have chosen articles that go deeply
`into the characteristics of a particul.ar hypertext sys-
`tem, attempt to generalize major concepts that define
`hypertext, or describe in detail a particular application.
`We hope the reader, beginning with a narrower but
`deeper understanding of hypertext, will be well pre-
`pared to read further in the literature, consider using
`hypertext
`for a specific application, or think about the
`many issues raised by this technology.
`The first two articles describe specific hypertext sys-
`tems. However, they extend their discussions to a num-
`ber of design issues that apply to all current and future
`systems. Akscyn, McCracken, and Yoder describe KMS,
`a large system that is commercially available.. In doing
`so, they examine the 26 key design decisions they
`made. This discussion not only provides a detailed view
`of KMS and its rationale but a very general view of the
`design space in which all hypertext systems fit. In the
`second article Halasz describes NoteCards, the system
`he helped to develop at Xerox PARC. In considering
`possible extensions to NoteCards, Halasz identifies
`seven key problems that currently
`limit hypertext sys-
`tems but which also provide goals for future research.
`The articles by Brad Campbell and Joseph Goodman
`and by Pankaj Garg attempt to generalize key concepts
`inherent in hypertext. Campbell and Goodman describe
`
`818
`
`Communications of the ACM
`
`July 1988 Volume 31 Number 7
`
`Facebook's Exhibit No. 1020
`Page 3
`
`

`

`(HAM) developed at
`the Hypertext Abstract Machine
`Tektronix.
`This system
`is a back-end hypertext
`server
`that supports operations on directed graphs with
`typed
`nodes and links. Consequently,
`it can be used to sup-
`port a number of different
`interfaces and applications.
`Garg offers a formal mathematical
`description of hyper-
`text. This work could
`link hypertext
`systems to other
`areas of research, such as relational databases and for-
`mal search languages, as well as lead to even more
`general
`tools for building hypertext
`systems.
`The last pair of articles consider
`two applications.
`Mark Frisse describes work underway at Washington
`University
`in St. Louis to develop a hypertext
`system
`for delivering medical
`information. Darrell Raymond
`and Frank Tompa describe a project at the University
`of Waterloo
`to build a hypertext
`version of the Oxford
`English Dictionary.
`these six articles were among
`During
`the conference,
`eight that provoked considerable discussion
`in terms of
`issues raised by hypertext. We overheard much discus-
`sion of legal issues. How can copyright
`issues be re-
`solved
`to permit development
`of large hypertext
`data-
`bases that can be searched,
`relevant material
`found,
`and reused in new documents? How can intellectual
`ownership be traced
`in such an environment? Others
`were concerned with social issues. As networks
`link
`more and more individuals
`and hypertext
`databases,
`will we create a further division between
`the included
`
`.’ ; SPECIAL
`1 1
`
`ISSUE
`
`.,,
`
`and the excluded? Most of this discussion, however,
`occurred outside
`the formal sessions. However, we
`hope this special
`issue will stimulate
`similar discussion
`among readers and their colleagues.
`John B. Smith
`Stephen F. Weiss
`Guest Editors
`The University of North Carolina
`Department of Computer Science
`Chapel Hill, N.C.
`
`2.
`
`3.
`
`and survey.
`
`IEEE Computer
`
`REFERENCES
`Bush. V. As we may think. A~lanfic Monthly 176. 1 (July 1945). pp.
`1.
`101-108.
`Conklin, E.J. Hypertext: An introduction
`2, 9 (Sept. 1987). 17-41.
`for CAD
`system
`Deli&, N. and Schwartz, M. Neptune: A hypertext
`In Proceedings of ACM SlGMOD International Conference
`applications.
`on Managemenf of Data (Washington, D.C., May 1986), ACM, New
`York. 132-143.
`for augmenting
`Engelbart, D.C., and English, W.K. A research center
`In Proceedings of the 1968 Fall Joint Computer Confer-
`human
`intellect.
`ence (Montvale. N.J., Fall 1968). kFlPS Press. 395-410.
`In Information Retrieval: A
`Nelson, T.H. Getting
`it out of our system.
`Crifical Review. G. Schechter, ed. Thompson Books. Washington.
`D.C.. 1967. 191-210.
`for professionals. Tech. Rep.
`Smith, J.B. WE: A writing environment
`86-025, Department
`of Computer Science. University
`of North Caro-
`lina at Chapel Hill, August 1986.
`Walker J.H. The Document Examiner. SIGGRAPH Video Review.
`Edited Compilation
`from CH1’85: Human Factors
`in Computing Sys-
`tems 1985.
`N., and van Dam A. Reading and writ-
`N., Meyrowitz
`Yank&s&h,
`ing the electronic book. IEEE Computer 18, 10 [Oct. 1985), 15-30.
`
`4.
`
`5.
`
`6.
`
`7.
`
`6.
`
`July 1988
`
`Volume
`
`31 Number 7
`
`Communications of the ACM
`
`819
`
`Facebook's Exhibit No. 1020
`Page 4
`
`