S U R V E Y & TUTORIAL SERIES

Hypertext: An Introductionand Survev

J

Jeff Conklin

Microelectronics and Computer Technology Corp.

ost modern computer sys-tems share a foundationwhich is built of directories

containing files. The files consist of textwhich is composed of characters. The textthat is stored within this hierarchy is linear.For much of our current way of doingbusiness, this linear organization is suffi-cicnt. Howcvcr, for morcand moreappli-cations, a linear organization is notadequate. For example, the documenta-tion of a computer program* is usuallyeither squcczcd into the margins of theprogram, in which case it is generally tooterse to be useful, or it is interleaved withthe text of the program, a practice whichbreaks up the flow of both program anddocumentation.

As workstations grow cheaper, morepowerful, and more available, new possi-bilities emerge for extending the tradi-tional notion of “flat” text files byallowing more complex organizations ofthe material. Mechanisms are beingdevised which allow direct machine-supported references from one textual

Hypertext systemsfeature machine-

supported links-bothwithin and between

documents-that openexciting new

possibilities for u!Gngthe computer as a

communication andthinking tool.

design issues that go into fashioning ahypertext environment.

graphically (as labelled tokens) and in thedatabase (as pointers). (See Figure I .)

But this simple idea is creating muchexcitement. Several universities havecreated laboratories for research on hyper-text, many articles have been written aboutthe concept just within the last year, andthe Smithsonian Institute has created ademonstration laboratory to develop anddisplay hypertext technologies. What is allthe fuss about? Why are some people will-ing to make extravagant claims for hyper-text, calling it “idea processing” and “thebasis for global scientific literature”?

In this article I will attempt to gc~ at theessence of hypertext. I will discuss itsadvantages and disadvantages. I will showthat this-new technology opens some very-

pioneers of hypertext, once defined it as ‘?i’exciting possibilii;es, particularly for newuses of the computer as a communication

chunk to another; new interfaces provide Tcorn ma onofnaturallanguageiejit’iiriih fand thinking tool. However, the reader-.*‘b’ I$ ‘-’the user with the ability to interact directly ‘_Ihe c&puter*s capacity for interacti&* _ who has not used hypertext should espcctwith these chunks and IO establish new s branching, or dynamic display. . . of arelationships bctwcen them. Theseexten- iL non~neartext_ . ~whichcannot~p,+.,t~sions of the’traditional text fall under ihe ”general category of hyperkxf (also known

conveniently on a conventional page.“’This article is a survey of existing hyper-

as noniineurfext). Ted Nelson, one of the text systems, their applications, and their

'D~cumm~a~ion is Ihe uncrccutablc English textdesign. It is both an introduction to the

which explains the logic of the program which it world of hypertext and, at a deeper cut, aaccompanies. survey of some of the most important

September 1987 0018-9162/81/o9ooM)11501.00~~961 IEEE

that at best he will gain a pcrccption ofhypertext as a collection of intcrcsting fca-cures. Just as a description of electronicspreadsheets will not get across the real elc-gancc of that tool, this article can only hintat the potentials of hypertext. In fact, onemust work in current hypertext environ-ments for a while for the collection of fea-

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that is common’io many hypertext systems Iis the heavy use of windows that have a :one-to-one correspondence with nodes in. .,the database. 1 consider this feature to be

A Iof secondary importance.

One way to delimit hypertext is to point

4 Bout what it is not. Briefly, several systemshave some of the attributes Sf hypertext

CL3 but do not qualify. Window systems fall, into this category; while window systems

do have some of the interface functional- ’

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Figure 1. The correspondence bctwccn windows and links in the display, and nodesand links in the dafabasc. In this example, each node in the hypertext database isdisplayed in a separate window on the screen when requested. The link named “b”in window A has been activated by a pointing device, causing a new window named“B” IO be created on the screen and filled wifh the text from node B in the data-base. (Gcncrall~. links can have names that arc different from the name of the

@~m~t;,3imilarly, most outline proces-sor’s (such as ThinkTank) do not qualify.They provide little or no support for refer-ences between outline entries, althoughtheir integrated hierarchical database andinterface do approximate hypertext betterthan the other systems that I have men-tioned. Text formatting systems (such asTroff and Scribe) do not qua!ify. Theyallow a tree of text fragments in separatefiles to be gathered into one large docu-ment; however, this structure is hierarchi-cal and provides no interface for on-linenavigation within the (essentially linear)document. Similarly, database manage-ment systems (DBMSs) have links of var-ious kinds (for example, relational andobject-oriented links), but lack the singlecoherent interface to the database whichis the hallmark o[ hypertext. _

fqS’~ideodisCie~~orb~~m~~g~.~ .., _Inode they point to.)

I,‘fhere is,&&in~~~~~~est in theext+& 6&3&i. $+Xztext to the~n$+~en&l &cept or. .

PIype&&in which_ th;&‘n;$ii wh’ich’~ ‘i“y’i

&-are i n&&k$ _. tog&h&, can be- &t,

-+raphiF, digitized speech, audio record-F r

’ISI@, picty~e;s, animatir+ film clips, and ,..

a ‘T; !.JE,

‘Sistimably tast&‘pdors and tactilcsentz. F itures to coalesce into a useful tool.

,_ _.“..--t --.-aAt thu pomt, httle has been done i

One problem with identifying the the design and engineering t

tial aspects of hypertext is that the term these additional modalities, i

“hypertext” !-I% been used quite loosely in ing capability which allows a nonlinear although many of the high-level design ;

the pas[20 years for many diffcrcnt collcc- organimtion of 1~x1. An additional feature issues arc likely IO be shared with hypcr-[ions of featurei. Such tools as window 1~x1. Thercforc, this survey will primarilysystems, elccrronic mail, and telecon- *While this arliclc seeks to establish the criterion cl address the more conservative text-based iferenckg share iearures with hypertext. mxhinc-supvrlcd links as the prims? crilcrion of systems.This anicle focuses on machine-supported

hypertext. this is by no means an xccp~rd definition.

links (both within and between docu-Thcrcforc I will also rcvicw 3nd discuss 3cvnc syrwnrwblch have a weaker notion 01 links. A glimpse of using hypcrtcxt. It is USC-

could claim that a file system is a database,and that one movef amongnodes(files) by i

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ful IO have a sense of the central aspects ofusing a hypertext system, particularly ifyou have never seen one. Below is a list of _the features of a somewhat idealizedhypertext system. Some existing systemshave more features than these, and some

and each has a name or title which,is always d&played in the window. How-ever, only a small number of nodes areyver “open” (as windows) on the screen atthe same time.l Standard window system operations

are supported: Windows can be reposi-tioned, resized, closed, and put aside as.small window icons. The position and sizeof a window or icon (and perhaps also itscolor and shape) arecues to rememberingthe contents of the window. Closing a win-dow causes the window to disappear afterany changes that have been made aresavedto the database node. Clicking with themouse on the icon of a closed windowcauses the window to open instantly,. ,_ ,. _.

.* Windows can contain any number of:Jink.ico,p+ thich repiesent-pointers toother nodes in the database. The link iconcontains a short textual field which sug-gcsts the contents of the node it points to.Clicking on a !ink icon with the mousecauses the system to find the referencednode and to immediately open a new win-

* Display s c r e e n wilh Wwsrr,

L -----__--____- 1Hypertext database

dow for it on the screen. ._ ._ : _,, l The user can easily create new nodes i

and new links to new nodes (for anhota-lion, comment; elaboration, etc.) or to

Figure 2. The screen at the top illustrates how a hypertext browser provides a direct

existing nodes (for establishing new con-two-dimensional graphic view of the underlying database. In this illustration, thenode “A” has been selected for full display of its contents. Notice that in the

nections). _,_..I

browser view you can tell not only which nodes are linked IO A but also how thel Thedatabasecaribebrdwsedin tliiii--“subnetwork fits into the larger hyperdocument. (Of course, hyperdocuments of an>

ways: (1) by following links and opening ‘size cannot be shown all al once in a browser-only portions can be displayed.)windows successively to examine their Con-_:? ‘_. -’tents, (2) bysearchingthe network (or pat-t -“. ’ i

of it) for some string,*+ keyword, or _+’attribute value, and (3) ‘by navigating i-around -theT%yperdocument using a- 5--browserthat displays the network graphi-

zcally. _The user can select whether thenodes and links display their labels or npf.

The browser is an importantcomponent

_<:rr”rcci”C”‘.Y---F$f hypertext syster+ As the hyperdocu-ment grows more complex, it becomes dis-tressingly easy for a user to become lost ordisoricntcd. A browser displays some or ailof the hyperdocument as a graph, provid-ing an important measure of contextualand spatial cues to supplement the user’smodel of which nodes he is viewing andhow they are related to each other and theirneighbors in the graph. (See Figure 2.)

‘NOIC 11131 I am arc dcscribrng two uses oficons: thoselhal function as placcholdcrs for windows that havebeen temporarily pur aside, and those within umdowsthal rcprcseni hnks IO other nodes.

‘*A wring 1s a scrics of alphabclic and numenc iharac-lcrs of any length, for example “liricning” or“CiOO274.”

September 1987

Using a browser can be likened to usingvisual and tactile cues when looking for acerfain page in a book. Sometimes wcrcmembcr the pcneral way rhc page lookedand about how far it was through thebook. although we don’t recall the pagenumber or even which keyword termswould help us find it by using the index ortable oicontenfs. The browser display canbe similarly scanned and scrolled when the

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user has forgotten all but the appearanceor location of a node.

Hypertextimplementations

hypcrtextual representation.But if one insists, as most modern

The history of hypertext is rich and var-proponents of hypertext do, that naviga-

ied because hypertext is not so much a newtion through hypertextual space must be

idea as an evolving conception of the pos-computer-supported in order to qualify as

sibleapplications of the computer. Manytrue hypertext, then the field is narrowed

people have contributed to the idea, andconsiderably, and the history likewiseshortened.

each of them seems to have had somethingdifferent in mind. In this section, I will

In some ways, the people who first

review these theorists and their ideas in andescribed hypertext-Bush, Engelbart,

effort to present a historical perspective asNelson-all had the same vision for hyper-

well as to sketch some of the hypertexttext as a path to ultimate human-computer

applications that have been devised tointeraction, a vision which is still alive

date. I do not describe the individual sys-today among hypertext researchers. Thus

terns and ideas reviewed here in any detail.the historical review below stresses the

For more detailed information, the readerearly development of ideas about hyper-

is invited to consult the literature directly.text as much as the more contemporary

, F”21_ m7 ,--: .‘.,.. .,_ _ _ . ‘~~“u; cpTp’ -7s !?@ementation e ffy *ne kmd of manual hypertext s the tra- .i Because of the difficulty of precisely

#&tional use of 3 x 5 index cards for notei taking. Note cards are often referenced’to-each other, as well as arranged hierarchi-

cally (for example, in a shoebox or inrubber-banded bundles). A particularadvantage of note cards is that their smallsize modularizes the notes into smallchunks. The user can easily reorganize aset of cards when new information sug-gests a restructuring of the notes. Ofcourse, a problem \vith note cards is thatrheuser can have difficulty finding a spe-cific card if he has many of them.

Another kind of manual hypertext is thereference book, exemplified by the dic-tionary and the encyclopedia. In the sensethat each of these can be viewed as a graphof textual nodes joined by referential links,they are very old forms of hypertext. Asone reads an article or definition, explicitreferences to related items indicate whereto get more information about those items.The majority of people’s transactions witha dictionary make use of the linear (alpha-betic) ordering of its elements (detkirions)for accessing a desired element. An ency-clopedia, on the other hand, can best beused rg explorGhe local nodes in the “net-work,” once one has found the desiredentry through the alphabetic index.

There are also many documents inwhich references io other parts of thedocumcnr. or IO other documents, consti-(MC a major portion oithc work. Both theTalmud, with its heat,! use of annotationsand nested commentary, and Aristotle’swritings, with their reliance on referencesto other sources, are ancient prototypesof

classifying hypertext systems according to*their features, my description will list sys-tems according to application. There arefour broad application areas for whichhypertext svstems have been developed:

20

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mucro lilerarysyslems: the study ofrechn’oiogies G’s&& l&e on-linelibraries in which interdocument linksare machine-supported (that is, allpublishing, reading, collaboration,and criticism takes place within thenetwork);problem ezploraffon Tookloo to

$support early unstructured thin ingon a problem when many discon-nectcd ideas come to mind (for exam-ple, during early authoring andoutlining, problem solving, and pro-gramming and design);

:- browsingJy~fems:sy;frems similar to%. ‘2 . ._.:macrolite’ra’rjsystem?, but smaller inscale (for teaching, reference, andpublic information, where ease of useis crucial); ~_. _.?-i).~..-r--. -I_ -

..* genirul hyp&G&hnologv. genera!“- ‘purpose.systenis designed to‘allow

experimentation with a range ofhypertext applications (for reading,writing, collaboration, etc.)

These categories are somewhat infor-mal. Often thesingle application IO whicha system has been applied to date derer-mints which category it is dcscribcd in.Bear in mind that some of the systemsmentioned below are full-scale environ-ments, while others are still only concep-tual sketches. Some systems have focusedmore on the development of thejronr end

“.. ._--_.______

(tic user interface a&s). while othershave focused on the database issues of thebuck end (the database server). Table Iidentifies various features of the differenthypertext systems which have been imple-mented.

Macro literary systems. The earliestvisions of hypertext focus on the inttgra-tion of colossal volumes of information tomake them readilyaccessible via a simpleand consistent interface. The whole net-work publishing system constitutes adynamic corpus to be enriched by readerswithout defacing the original documents;thus, the difference between authors andreaders is diminished. The advent of thecomputer has brought this vision closer IO

reality, but it has also revealed themonumental problems inherent in thisapplication area.

Bush 3 Memex. Vannevar Bush, Presi-dent Roosevelt’s Science Advisor, iscredited with first describing hypertext inhis 1945 article “As We May Think,“’ inwhich he calls for a major postwar effortto mechanize tht scientific literature sys-tem. In the article, he introduces a machinefor browsing and making notes in anextensive on-line text and graphics system.This memexcontained a very large libraryas well as personal notes, photographs,and sketches. It had several screens and afacility for establishing a labelled linkbetween any IWO points in the entirelibrary. Although the article is remarkablyforesightful, Bush did not anticipate thepower of the digital computer; thus hismemex uses microfilm and photocells todo its magic. But Bush did anticipate theinformation explosion and was motivatedin developing his ideas by the need to sup-port more natural forms of indexing andretrieval:

The human mind . . . operates by associa-tion. Man cannot hope fully IO duplicate this

mental process arMicially, but he certainlyPugh1 IO be able IO learn from it. One cannothope IO equal the speed and flexibility withwhich the mind follows an associative trail.but it should be possible to-beat ~hGainddecisively in regard to the pcrmancnc< andclarity of the items resurreclcd fromstorage.’

Bush described the essential feature of:he mcmcx as the ability to tic IWO ircmstogcrhcr. The mechanism is complex, burclever. The user has IWO documents that hewishes to join into a trail he is building,each document in its own vicwcr; hc rapsin rhc name of the link, and that nameappears in a code space at the bottom of

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HypertextSystems

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Emacs INFO

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Hierarchy Graph- Link Attri- Paths Vcr- Proced- Keyword Text Con- Pictures Graphicabased Types butes sions ural or Editor current or Browser

Attach- String Multi- Graphicsment Search users

Yes Yes Fixed' No’ No No Yes Yes Emacs No Yes Yes.

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

Yes No No No No No No Yes Emacs Np No No

Yes Yes Yes No No Byiink No No A basic Yes No’. Notextcdilor

Intermedia YeS Yes Yes Yes No’ No No’

KMS Multiple Yes Fixed No No’ Yes Yes

Neptune Yes Yes Yes Yes No Yes Yes

NLS/Augment Y e s Yes Yes Yes Yes Yes Yes

NoteCards Multiple Yes Yes Nodes No No Yes

3utline Processors Yes No No No No No No

PlaneText Unix Yes No No No h‘o Nofile sys.

jymbolics Yes Yes No No Yes No No3ocumentExaminer

Yes

Yes

Yes

Yes

Yes

Yes

Unix/grep

Yes

Custom Yes Yes Yei

Text/ Yes Yes Nograph.WYSIWYG

Smalltalk- Yes Yes Yei80 editor

Custom Yes Yes No

Interlisp Yes Yes YCi

Various No No N O

SunView Yes Yes Yeitext ed.

None No No N O

XNVIEW

rexmet

iyperties

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Yanadu

ZOG

Yes No No No No h’o No No linccd.1 No No N O

Unix

Multiple Yes Yes Yes Yes h’o No Keyword Any No No N O

No Yes No No No No No No’ A basic No Yes Notext edilor

Yes Yes No Fixed No* No: No’ No Smalltalk- No’ Yes Yei80 editor

No Yes Yes Yes Yes Yes No No Any No Yes No

Yes No No No No No Yes Full text Spec. Pur. Yes No N O

’ Can be user programmed.’ Planned for next version.

-In this table, each column rcprcs?nts one possible feature or ability that a hypertext systun can provide. The negative or affirmalive enws in rhe-3able indicate whether the corresponding hypertext system meets the standardcrireria for a specified fealurc. These criteria are lisred bclo\v.

Hierarchy: Is there specific support for hierarchical smcturcs?Graph-based: Does the sys[cm support nonhierarchical (cross-reference) links?Link types: Can links have types?Al[ributes: Can user-designated attribute/value pairs be associated \\ith nodes or links?Palhs: Can many links be srrung togcthcr inlo a single persistent objca?Versions: Can nodes or links have more than a single version?Procedural attachment: Can arbitrary csccurablc procedures bc atrachcd IO events (such as mousing) a~ nodes or links?.%ring search: Can the hypcrdocumcnr be searched for strings (including keywords)?TCXI cdilor: What cdilor is used IO create and modify the comems of nodes?Concurrent mul[iusers: Can scvcral users edit the hypcrdocument at Ihc same lime?Plclurcs or graphics: Is some form of piclorial or graphical informalion supporrcd in addition IO ICXL?Graphics browser: Is there a browser which graphically presents [he nodes and links in rhe hypcrdocumenr?

September 1987t

,-

-

Figure 3. Engelbart 31 fhe NLS/Augmenf workstation. Note the chord key se1under Engelbart’s left hand. The chord key set is optional for Augment. If is aremarkable accelerator for character-driven commands and mouse-select screenoperands.

each viewer; out of view, the code space isalso filled with a phoroccll-rcadablc dotcode that names the other document andthe current position in that document.Thereafter, when one of these items is inview, the other can be instantly recalledmerely by tapping a button below the cor-responding code space. Bush admitted thatmany technological breakthroughs wouldbe needed to make his memex practical,but he felt that it was a technologicalachievement worthy of major expenditure.

Engflban’s M!.S/Augmenr. Just lessthan two decades later Douglas Engelbart,at Stanford Research Institute, wasinfluenced by Bush’s ideas. In 1963. Engel-bart wrote “A Conceprual Framework forthe Augmcntarion of Man’s Intcllcct.“’Engelbart envisioned that computerswould usher in a new stage of human evo-

- luiron, c h a r a c t e r i z e d b y “aulomatcdcsrcrnal symbol manipulation”:

22

In this stage. the symbols with which thehuman tcprcscnts the conccps he is manip-ulating can be arranged before his eyes,moved. stored, recalled, operated uponaccording IO extremely complex rules-all invery rapid response IO a minimum amoum ofinlormation supplied by the human, bymeans of special cooperative technologicaldevices. In the limit of whal we might nowimagine, this could be a computer. withwhich individuals could communicate rapidlyand easily, coupled to a three-dimensionalcolor display with which extremely sophisti-caled images could be constructed . . .)

ideas about augmentation had becomemore specific, and had been implementedas NLS (ON Line System) by the Augmen-ted Human Intellect Research Center atSRI. NLS was designed as an experimen-tal tool on which the research group devel-oped a system that would be adequate toall of their work needs, by

placing in computer store all of our speci!i-cations, plans, designs, programs, documen-tation. reports, memos, bibliography andrcrerence notes, etc., and doing all of ourscratch work, planning, designing, debug-ging, erc., and a good deal of our intercom-munication, via the consoles.‘

These consoles were very sophisticatedby the standards of the day and includedtelevision images and a variety of inputdevices, including one of Engelbart’s bestknown inventions, the mouse:

Files in NLS were structured into a hier-archy of segments** called slafements,each of which bore an identifier of its levelwithin the file. For example, a documentmight havestatements”l,““la,” “.lal.”“la&” “ 1 b,” etc., though these identi-fiers did not need to be displayed. Anynumber of reference links couldbe estab-lished between statements within files andbetween files. Note that this is a structurewhich is primarily hierarchical, but whichallows nonhierarchical links as well. Theimportance of supporting both kinds ofstructures is a point to which I will returnlater. The system provided several ways totraverse the statements in files.

NLS, like other early hypertext systems,emphasized three aspects: a database ofnonlinear text, viewfilrers which selectedinformation from this database, and viebctswhich structured the display of this infor-mation for the terminal. The availabilityof workstations with high resolution dis-plays has shifted the emphasis to moregraphical depictions of nodes, links, andnetworks, such as using one window foreach node.

His p roposed sysrem, -AM/T(Human using Language, Artifacts, andMethodology, in which he is Trained),included the human user as an essential ele-ment: The user and the computer weredynamically changing components in asymbiosis which had the effect of“amplifying” the native intelligence of theuser. This is still a common vision amongdcvclopcrs of hypcrrcst systems.

NLS provided viewing filters for the filestructure: One could clip the level (depth)of hierarchy displayed, truncate the num-ber of items displayed at any level, andwrite customizedfilters (in a “high-levelcontent analysis language”) that displayedonly statements having the specified con-tent. NLS also introduced the concept of

Five years later, in 196s. Engclbart’s “Scamcn~r wxc llmaicd IO 3CCOcharac~rrs m Icngh.

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NLS has evolved over the years. It isnow called Augment (or NLS/Augment)and is marketed as a commercial networksystem by McDonnell Douglas. Indeveloping NJ_& the emphasis has been oncreating a consistent environment for*‘knowledge workers” (that is, officeautomation for software engineers). Thesystem now includes many forms ofcomputer-supported communication,both asynchronous (email with links to alldocuments, journaling of ideas andexchanges, bulletin boards, etc.) and syn-chronous (several terminals sharing thesame display, teleconferencing, etc.). Itincludes facilities for document produc-tion and control, organizational and pro-ject information management, andsoftware engineering. (See Figures 3 and4.)

Nelson’s Xanadu Projecf. DuringEngelbart’s development of Augment,another hypertext visionary, Ted Nelson,

was developing his own ideas about aug-mentation, but with an emphasis on creat-ing a unified literary environment on aglobal scale. Nelson coined the term“hypertext.” His thinking and writing arethe most extravagant of any of the earlyworkers. He named his hypertext systemXanadu, after the “magic place of literarymemory” in Samuel Ta; lor Coleridge’spoem “Kubla Khan.” InXanadu, storagespace is saved by the heavy use of links.Only the original document and thechanges made to it are saved. The systemeasily reconstructs previous versions ofdocuments. Nelson describes his objec-tives as follows:

Under guiding ideas which are not technicalbut Iilcrary, weareimplemenringa system forstorageand retrieval of linked and window-ing text. The document, our fundamentalunit, can have windows to any other docu-ments. The evolving corpus is continuallyexpandable wifhoul fundamental change.h’cw links and windows can continually addnew access pathways M old mPerial. Fastproprierary algorithm? render the extremedala fragmentalion tolerable in the plannedback-end service facility.’

The long range goal of the Xanadu pro-ject has been facilitating the revolutionaryprocess of placing the cntirc world’s liter-ary corpus on line. In fact, Xanadu’sdesign makes a strong separation betweenIhc user imcrfncc nnd the dntnbnsc scrvcr.with most of the emphasis placed on thelatter. In particular, great care has beentaken that copyright protection is main-

September l9S7

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Figure 4. Augment display showing five windows. Window 1 (W-l) has a passageas if embedded in a message, showing a link to Branch 7c of Document 2250 in theOAD Journal. A ViewSpcc (“rbtzgm”) provides Ihc following spccific:,iions: tar-get level plus one, 1runcaIe to one line per statement, no blank lines beIcccn stale-men& show only Ihat branch (e.g., noI Branch 7d), and Iurn on LocationNumbers. Window 2 (W-2) shows the view obtained with a jump link command.To perform a jump link command, Ihe opcralor clicks on Ihc link in W-1, lbcnmoves the cursor into W-2 for Ihc final click. Thr very fop-lcf~ syslcm rncssagcannounces that the desired Journal Item has been accessed, and Ihc clusIcr al Ihetop left of the screen verifies that the view is clipped to three levels and the state-ments truncated to one line each. Window 3 (W-3) shows an indirecl link fhatspecifies Ihe linkage palh. In effect, this link says “go to the statemen! in the filenamed ‘Refd,’ follow the link found there to iIs target file, and in Ihat file findLocation Number 6.” Kale IhaI Ihe same ViewSpec is specified here as for Ihc linkin W-l. Window 4 (W-4) identifies Refd and provides its general reference sourceas the reference section at the end of !he document; a user can jump from Ihe linkcitation in W-3 IO see Ihis statement by using the jump name command. To pcr-form this command, he clicks on “Ref-6” in W-3 then clicks on W-4. Window 5

(W-S) shows a view in the OAD-Journal Item 2250. The user can obtain this viewby performing a jump link command on the indirect link of W-3. To perform thiscommand, the user clicks on lhe indirect link of W-3 and then clicks in W-S.

tainablc, and that a system for the clcc-Ironic accounting and distribution ofroyalties is in place. Nelson predicts thatthe advent of on-line libraries will crcatca whole new market for the organizationand indexing of this immense informationstore.

The back end of the Xanadu system hasbeen implemented in Unix and is availablein several forms, including as an on-lintscrvicc (much like Engclbnrt’s Augnicn~).A crude front end for the Xanadu systemis also available which runs on Sun work-stations.

i

.. Trigg’s Textnef. Randall Trigg wrot;

the first and to date the only PhD thesis onhypertext. In his thesis, he describes hisTextnet system as supporting nonlinear~exl-text in which documents areorganized’as “primitive pieces of text con-nected with typed links to form a networksimilar in many ways to a semantic net.”The thesis focuses on specific link typesthat support literary criticism.

In the tradition of the field, frigg’s sys-tem is just a first step in the direction of hisvision:

In our view, the logical and inevitable result[of the comp\.ctr revolution] will be the tram-fer of all such (text handling] activities to thecomputer, transforming communicationwithin the scientific community. All paperwriting, critiquing, and refereeing will be pcr-formed on line. Rather than having to trackdown litllc-known proceedings, journals orunpublished technical reports from distantuniversities, users will find them stored in onelarge distributed computerized nationalpaper network. New papers will be writtenusing the network, often collaborated on bymultiple aurhors. and submitred IO on-lineelectronic journals.‘

Textnet implements two basic types ofnodes: those which have textual content(chunks) and those which hierarchicallyorganize other nodes (foes, for “table ofcontents”). Thus Textnet supports bothhierarchical trees (via the tot nodes) andnonhierarchical graphs (via the typedlinks).

Trigg further proposes a specific tax-onomy of link types for use by collabora-tors and critics in Textnet. He argues thatthere is generally a specific set of types ofcomments, and that there is a link type foreach comment. For example, there arere_futalion and supper/ links, and, morespecifically, thcrc arc links to say that apoint is irrelevant (“Pt-irrelevant”), thatd a t a c i t e d i s i n a d e q u a t e (“D-inadequate”), or that the styleis rambling(“S-rambling”). Trigg describes over 80such link types and argues that the disad-vantage of having a limited set of link typesis outweighed by the possibility of special-ized processing on the hyperdocumentafforded by a definite and fixed set ofprimitives.

In addition, Textnet sworts the defi-nition of pafhs-ordered lists of nodes-used to browse linear concatenations oftext and to dump such scans to hard copy.The path facility relieves the hypertextrcadcr from having to make an n-~aydcci-sion at each link; rarhcr, the rcadcr isprovided a default pathway through thenetwork (or part of the network), and cansimply read the material in the suggested

24

order as if he were reading a lineardocument.

Trigg joined Xerox PARC after com-pleting his thesis and was one of the prin-cipal architects of the Xerox NoteCardssystem.

Problem exploration systems. These arehighly interactive systems which providerapid response to a small collection ofspecialized commands for the manipula-tion of information. They can be thoughtof as the early prototypes of electronicspreadsheets for text and symbolicprocessing. One important feature of mostof these tools is a facility for suppressingdetail at various levels specified by theuser. For example, the outline processorsall have single keystroke commands forturning on and off the display of subsec-tions of a section. This is an unusual butnatural facility. Hypertext and similartools excel at the collection of largeamounts of relatively unstructured infor-mation. But such cohections are of littleuse unless adequate mechanisms exist forfiltering, organizing, and browsing. Theseare the primary desiderata of these author-ing/thinking/programming systems.

Issue-Based Informorion Systems.Horst Rittel and his students have intro-duced the notion of issue-Based Informa-tion Systems (IBIS)’ to handle systemsanalysis in the face of “wicked problems.”Rittel describes wicked problems (asopposed IO “tame” ones) as problemswhich cannot be solved by the traditionalsystems analysis approach (that is, (1)define the problem, (2) collect data, (3)analyze the data, (4) construct a solution).Wicked problems lack a definitive formu-lation; their problem space cannot bemapped out without understanding thesolution elements; in short, the only wayto really understand a wicked problem isto solve it. Wicked problems have no stop-ping rule. The design or planning activitystops for considerations that are externalto the problem (for example, lack of time,money, or patience). Solutions to wickedproblems are not “right” or “wrong”;they just have degrees of sufficiency. Rit-tcl argues that solving wicked problemsrequires all those involved IO exchange andargue their many viewpoints, ideas,values, and concerns. By coming IO under-stand other viewpoints bcrter. each par-

ticipant is able lo understand the wholeproblem better. 776s process enables acommon understanding of the majorissues and their implications to emerge.IBIS is designed to support thisdesign/planning conversation.

IBIS systems are thus a marriage of (1)teleconferencing systems which enablemany people to participate in one conver-sation, and (2) hypertext, which allowsparticipants to move easily between differ-ent issues and the different threads ofargument on the same issue. The currentversion of Rittel’s IBIS runs on an ApplePC and is being ported to Sun worksta-tions.* IBIS has three types of nodes(issues, posifions, and arguments), anduses nine types of relations to link thesenodes. In a typical application, someoneposts an issue; then that person or otherspost positions about that issue; and thenthe positions are argued using argumentnodes. Of course, any of the three types ofnodes can be the seed of a new issue. (SeeFigure 5.) The current set of relationshipsbetween nodes is: responds-to, quesrions.supports, objects-to, specializes, general-izes, refers-to, and replaces. Theresearchon IBIS concentrates 0~1 ways to summa-rize and present the issue network, bothfor participants and decision makers.

Lowe’s SYNVIEW. David Lowe’sSYNVIEW system is similar in concept toRittel’s IBIS but goes in a different direc-tion. It proposes that the participants, inaddition to posting their own issues andarguments, assess previous postings as totheir validity and relevance. The asscss-ment is done by a kind of quantitative vot-ing. For example, if you think that Joe’srcsponsc to Sam makes a good point butis not really a direct response to Sam’sposting, you might grade it “5, 1” (where5 is a high validity rating and 1 is a low rel-evance rating). These values are averagedinto the existing values for that posting.The various displays of the argumentstructure show the values for each posting,allowing readers to focus, if they chooseto, on those argument trails having thehighest voted validity.

Thro@h debate>on the accuracy of informa-tion and on aspccls of rhc structures thcm-selves, a large number of users cancooperatively rank al1 available irems ofinformation in lcrms of significance and rcl-cvancc IO cxh topic. Individual users canlhcn choose the depth IO which ~hcy wish IO

csaminc [hcsc s~ruc~urcs for IIIC purposes 31

‘A graphical Sun version. allcd glL3lS. is also beingdewloped ;I, the hlCC/Softwnrc Tcchnolog)I’rogrLJm.

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UNC’s WE. A group at the Unjversityof North Carolina at Chapel Hill has beendeveloping a wrifing environmen! calledWE.9 Their research is based on a cogni-tive model of the communication processwhich explains reading as the process oftaking the linear stream of text, compre-hending it by structuring the concepts hier-archically, and absorbing it into long-termmemory as a nefwork. Writing is seen asthe reverse process: A loosely structurednetwork of internal ideas and externalsources 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 upstreampart of writing. It contains two major viewwindows, one graphical and one hierarchi-cal, and many specialized comman_ds formoving and structuring material (nodesand links with attached text) between thesetwo views. Normally a writer will begin bycreating nodes in the graph view, where hecan place them anywhere within the win-dow. At this stage, little or no structure isimposed on the conceptual material. Thewriter can place nodes in “piles” if theyseem to be related, or he can place individ-ual nodes between two piles if they aresomewhat related to both. As some con-ceptuzl structure begins to emerge fromthis process, the writer can copy nodes intothe hierarchy window, which has spccial-ized commands for tree operations. Thehierarchy window has four different dis-play modes: (1) the tree can be laid out onits side, with the root node on the left; (2)the tree can be hung vertically with the rootat the top; (3) child nodes can be displayedinside their parent node; and, (4) the hier-archy can be shown in the traditional out-line view.

WE uses a relational database for thestorage of the nodes and links in the net-work. The user points with a mouse toselect a node. A third window is an editorfor the material within the currentlyselected node. A fourth window on thescreen is for queries to the database. Afifth window is used to control systemmodes and the current working set ofnodes.

WE is designed to be an experimentalplatform to study what tools and facilitieswill be useful in a writer’s environment.The real validation of these ideas, as withso many of the systems described here, will

Septcmbcr 19S7

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Figure 5. A segment of a possible IBIS-style discussion showing the topology of theIBIS network. Each node contains information on the type of the node, the timeand date of creation, the author, a short phrase describing the content, a longerbody of text with the text of !hc comment, a list of keywords, nnd a list of theincoming and outgoing links.

come with further experiments andanalysis.

Outlineprocessors. An outlineproces-sor is a word processing program which isspecialized for processing outlines, in thatits main commands deal with movementamong, creation of, and modification ofoutline entries. In this respect, thesepro-grams commercialize many ideas fromEngelbart’s NLS/Augment. Outlineprocessors also have at least simple texteditors and do some text formatting, sothat the user can use the same tool to gofrom outline to finished document. One ofthe most powerful features of outlineprocessing is the ability to suppress lowerlevels of detail in the outline. As withEngelbart’s NLS/Augment, the user canview just the top level of the outline, or thetop n levels, or he can “walk the tree,”

opening up just those entries that are rele-vant or useful to the idea that he is work-ing on. In addition, each outline entry canhave a textual body of any lengthassociated with it, and the user can makethis body appear or disappear with a sin-gle keystroke. This feature is a real boonto the writing process, becauseit allows the

%ser IO have a view of boththe immediatetext that he is composing and the globalcontext for it. It also facilitates rapidmovement between sections, particularlyin large documents, because in outlinemode a rcmotc section is ncvcr more thana few keystrokes a\vay.

Most outline processors are personalcomputer programs, and they have donemuch IO bring some of rhe concepts undcr-lying hypertext into popularity. The firstof these was called ThinkTank. II wasreleased in 1984. It has since been joiner’

..

by a host of others, with names like Max-Think, Executive Writer/Executive Filer.Thor , Framework , Kamas , Fac tCruncher, Freestyle, Idea!, and PC-Outlinc.‘“There are two very recent addi-tions to the field: Houdini is an extensionof MaxThink that supports rich nonhicr-archical internode references; and For-Comment is a word processor that allowsup to 15 people to apply hypertext-likeannotations to a document (and can opcr-ate over a Local Area Network (LAN) inreal time).

Aside from Houdini, most outlineprocessors do not support inter-entryreferences, except by “cloning” the wholeentry and displaying it in the new location.Only a few others provide windows fornodes. None of them provide explicit“mousable” link icons. For these reasons,one could argue whether they qualify ashypertext as I have defined it here. How-ever, ThinkTank was the first program tobe billed-somewhat pretentiously--as an“idea processor,” and all of these pro-grams treat sections of text as first-classobjects and support manipulations thatcoincide with the way one manages ideas.They share these features with hypertext,and in this sense, they anticipate theinevitable proliferation of hypertext fea-tures within the mainstream of computerapplications.

Structured browsing systems. The sys-tcms rcvicwcd in this section wcrc dcsigncdprimarily for applications involving largeamounts of existing informarion or requir-ing easy access IO information. These sys-tems pose different problems for theirdesigners. Ease of learning and ease of useare paramount, and great care goes intocrafting the interface. On the other hand,writing (adding new information) isusually either not allowed to the casualuser or is not particularly well supported.

CMU’s ZOG and Knowledge Sysfems’KMS. ZOG is a menu-based display sys-tem developed in 1972 at Carnegie-hlellonUniversity.” It consists of a potentiallylargedatabase of small (screen-sized) seg-ments which are viewed one at a time.ZOG was developed with the particulargoal of serving a large simultaneous usercommunity, and thus was designed IO

operate on standard terminals on a largetimesharing system. In 1981 two of theprincipals on the ZOG Project, DonaldMcCracken and Robert Akscyn, startedthe c o m p a n y Knowlcdgc Sysrcms nnddevclopcd a commercial successor to ZOG

26

called Knowledge Management System(KMS).

Each segment of the ZOG/KMS data-base is called a frume. A frame has, byconvention, a one-line title at the top of thescreen, a few lines of text below the titlestaring the issue or topicof the frame, asctof numbered (or lettered) menu items oftext called selecfions, and a line of stand-ard ZOG commands called globolpadsatthe bottom of the screen. (Some of thesecommands are: edif, help. back. nexl,mark, refurn, and commenf.) The selec-tions interconnect the frames. When a userselects an item by typing its number or let-ter at the terminal keyboard, the selectedframe appears on thescreen, replacing theprevious frame. The structure is generallyhierarchical, though cross-referencinglinks can be included. In addition, an itemin a frame can be used to activate aprocess.

In 1982 ZOG was installed and used asa computer-based information manage-ment system on the nuclear-powered air-craft carrier USS CARL VINSON. Thissystem is probably the largest and mostthoroughly tested hypertext system in sew-ice in the field. ZOG has also been used formore interactive process applications suchas policy analysis, authoring, communica-tions, and code management. Historically,however, ZOG made its name more as abulletin board/textual database/CA1 toolthan as an interactive system. Hence it isincluded in this section on browsing. Adrawback of the ZOC/KMS style of view-ing a single frame at a time is that usersmay become disoriented, since no spatialevent corresponds to the process of mov-ing from frame to frame. In the KMS sys-tem, this tendency has been offset byminimizing system response time, so thatframe-to-frame transition takes about halfa second. Thepossibility of user disorien-tatio& greatlyreduced by the fact that theuser can move very quickly among framesand thus become reoriented with very lit-tle effort. Creating text and graphics is alsofast in KMS.

Emacs INFOSubsysrem. The help systemin the widely used text editor, Emacs, iscalled INFO. and is much like ZOG. It hasa sirnplcr set of standard commands, 31x4its control input is done by single letters or

-.,. _..

short commands typed at the keyboard. Itis primarily hierarchical, but a user canjump to a different place in the hierarchyby typing in the name of the destinationnode. It is used as an on-line help systemin Emacs. INFO has the same potential foruser disorientation which is shared by allof the systems which display only a singleframe at a time and have no browser.

Shneiderman 3 Hype&s. The Univer-sity of Maryland Hyperties project’ hasbeen developed in two directions-as apractical and easy-to-learn tool for brows-ing in instructional databases and as anexperimental platform for studies on thedesign of hypertext interfaces. As a prac-tical tool, it has already seen some use inthe field at a Washington, D.C. museumexhibit about Austria and the Holocaust.(See Figure 6.) Designers of the exhibitemphasized making the system easy andfun for users who have never used a com-puter before. As an experimental plat-form, it has been used in tive experimentalstudies involving over 228 subjects.”

In Hyperties the basic units are shortarticles (SO-1000 words typically), whichare interconnected by any number of links.The links are highlighted words or phrasesin the article text. The user activates thelinks by touching them with a finger (on atouch-sensitivescreen) or using the arrowkeys to jump to them. **Activating a linkcauses the article about that topic toappear in its own window on the screen.The system keeps track of the user’s paththrough the network of articles, allowingeasy return from exploratory side paths.

In addition to a title and a body of text,each article has a short (5- IO 25-word)description which the program can displayvery quickly. This feature allows the useran intermediate position between bringingup the full article and trying to guess fromthe link name precisely what the article isabout.

Hyperties runs on the IBM PC.Recently graphics capabilities have beenadded to the system. Current implementa-tion efforts focus on support for videodiscimages. Also. a browser is being developed

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Symbolics Docurnenf E&miner. Themost advanced of [he on-line help systems,ihis tool displays the pages from the entiretwelve-volume manual set on the Sym-bolics Lisp machine screen.” Certain tex-tual fields in the document (printed inbold) are mouse-sensitive. Touching oneof these fields with the mouse causes therelevant section of the manual to be addedto the current working set of manualpages. The system allows the reader toplace bookmarks on any topic and to moveswiftly between bookmarked topics. Theprotocol for link following is tailored tobrowsing in a refcrencc manual or cncy-clopedia. Mousing a link only causes it 10be placed on a list of current topics. Then,mousing an entry in this list causes thatlink to be followed, bringing up the refer-enced ropic in the main viewing window.

The system also supports on-line stringsearch of preidentified keywords, includ-ing the search for whole words, leadingsubsrrings, and embedded substrings. Thesystem is thus well designed for the specifictask of browsing through a technical man-ual and pursuing several aspects of a tech-nical question or several levels of detailsimultaneously. The user cannot makeanychanges or additions to the manual set(although it is possible to save personalizedcollections of bookmarks).

General hgpcrtcxt technology. So far Ihave discussed hypertext sysrems that haveparticular practical applicarions. The fol-lowing systems also have one or moreapplications, but their primary purpose isexperimentation with hypertext itself as atechnology. For example, whileNoteCards has been used for authoring,programming, personal information man--rgement, project management, legalresearch, engineering design, and CAI, itsdevelopers view it primarily as a researchvehicle for the study of hypertext.

.--,.Xerox PARC’s NoteCards. Perhaps the

best known version of full hypertextis theJ’oreCurds system developed at XeroxPr\RC.” The original motivation inbui ld ing NotcCards MS IO dcvclop nninformation analyst’s support tool, oneIhat would help gather information abouta topic and produce analytic reports. Thedesigners of Notccards observed rhat aninformation analyst usually follows ageneral procedure rhar consists of a series

September 1987

;:.G: lZ?e.choslouakia

PIACES: AUSTRlA PAGE 1 OF 3

Austria (see map) holds a special place in the history of the Holocaust. /

Situated between Eastern and Western Europe, possessing a vibrant and

culturally creative Jewish community on the eve of World War II. 1

Austria had also provided the young Adolf Hitler, himself an Austrian

raised near Linz. with impor’ant lessons in the political uses of

antisemitism Leading Nazis came from Austria: the names of Adolf

HiUer, Adolf Eichmann, wno organized the deporlations of the Jews to

the death camps, and Ernst Kaltenbrunner. the head of the

Reich Main Office for Security, 1943-45. readily cOme to mind. As~~_~_.______~~______~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Linz - city in northern Austria; childhood home of Adolf Hitler and other

lea&n9 Nazis

NEXT PAGE RETURN TO GYPSIES INDEX

-

Figure 6. The Hyperties Browser enables users to traverse a database of articles andpiclures by selecting from highlighted items embedded in the text of the arlicles.The photos show the IBM PC version of Hyperties. The upper node shows a mapof Austria. The lower node shows double-spaced text with link terms h ighl ighted .Either a touchscrccn or jump-arrow keys arc usrd for selection of hrirf dcfinitiolls,full articles, or pictures. The Hypertics Author permits pcoplc with onl! word

processing skills to create and maintain databases. Research versions of Hyperliesrun on the Enhanced Graphics Adapter to give more lines and multiple windowsand on the Sun 3 \vorkstation to show two full pages of 1~x1 31 a time. Currentdevelopment efforts will enable rcadcrs to point at pictures and videodisc images IO

ret r ieve fur ther in format ion.

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ofsteps: (1) reading sources (news reports,scholarly articles, etc.), (2) collecting clip-pings and filing them (in actual shoe-boxes!), and (3) writing analytic reports.The-designee also observed that through-outThe process, the analyst forms analysesand conceptual models in his head. Theresearch goal of the PARC team was todevelop technology to aid the analyst informing better conceptual models andannl\xcs, ntld to find bcrrcr cxprcssions oiIhcse models and analysts.

A programmer’s interface makesJoteCards an open architecture that

allo\rs users to build (in Lisp) new appii-cations on rap of NoteCards. Using this

28

interface, the user can easily customizethebrowser. NoteCards allows easy creationof new types of nodes. Forty or fifty suchspecialized node types have been createdto date, including text, video, animation,graphics, and actions. l The new versionalso allows several users IO work in thesame Notefile at the same time.

Part of NoteCards’ success is due to thefact that it was dcvclopcd on Xerox D-scrics Lisp machines, which 3rc powerfulworkstations that have high resolution

screens allowing windows and link andnode icons to be displayed in very highresolution. (See Figure 7.) Currentlybetween 50 and 100 users use NoteCards,many of them outside df Xer&eventhough it is not a supported product).Several of these users have constructedvery large databases in the system (foresample, 1600 nodes with 3500 linksbctwccn them).

Brown L'rriversily ‘s fntermedia. One ofthe oldest and largest hypcrtesr researchgroups esists at Brown University, at theInstitute for Rcscarch in Information andScholarship, (IRIS).” The lnrermcdia

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The first system was the Hypertext Edit-ing System designed by Ted Nelson, Andyvan Dam, and several Brown students forihC IBM 2250 display in 1968. This systemwas used by the Houston Manned Space-craft Center to produce Apollo documen-tation.

The second system was the File Retrievaland Editing System (FRESS). FRESS wasa greatly enhanced multiterminaltimesharing version designed by van Damand his students. It became available in1969 and was commercially reim-plemented by Phillips in the early 1970’s.FRESS was used in production byhundreds of faculty and students overmore than a decade. Its users included anEnglish poetry class that did all of its read-ing and writing on a communal hypertextdocument. Like NLS, FRESS featuredboth dynamic hierarchy and bidirectionalreference links, and keyworded links andnodes. Unlike NLS, it imposed no limitson the sizes of nodes. On graphics termi-nals, multiple windows and vectorgraphics were supported.

The third project, the Electronic Docu-ment system, was a hypermedia systememphasizing color raster graphics andnavigation aids.

As part of Brown’s overall effort tobring graphics-based workstations intoeffective* use within the classroom, theIntermedia system is being developed as aframewtjrk for a collection of tools thatallow authors 10 crcatc links to documentsof various media such as text, timelines,diagrams and other computer-generatedimages, video documentaries, and music.Two courses, one on cell biology and oneon English literature, have been taughtusing the system. Current applicationsinclude InterText, a text processor;InterDraw, a graphics editor; Interval, atimeline editor that allows users interac-tively to organize information in time anddate sequences; Int_erSpec, a viewer forsections of 3D objects; and InterPix, ascanned-image viewer. Under develop-ment are a video editor, a 2D animationeditor, and more complex methods forfiltering the corpus and creating andtraversing trails.

Intermedia is being developed both as atool for professors to organize and presenttheir lesson material via computer and asan interactive medium for students tostudy the matcrials and add their ownannotations and reports.

Scptcmbcr 1987

.I , _ ::.. _

For example, in the English lireraiurecourrethe firsr time a student is searching for back-ground informationon Alexander Pope, heor she may be interested in Pope’s life and thepolitical events that prompted his satiric criti-cism. To pursue this line of thought the stu-dent might retrieve the biography of Popeand a timeline summarizing political evenis

. taking place in England during Pope’s life.Subsequently, thestudent may want tocom-pare Pope’s use of satire with other laterauthors’satiric techniques. This time the stu-dent may look at the same information aboutPope but juxtapose it with information aboutother satiricists instead of a time line. Theinstructor (and other students. if permitted)could read the student’s paper. examine therefcrencc material, and add personal anno-tation links such as comments, criticism, andsuggestions for revision. While revising thedocument, the student could see all of theinstructor’s comments and examine thesources containing the counter-arguments.

Like most of the serious workers onhypertext, the Intermedia team is espe-cially concerned with providing the userwith ways of managing the increased com-plexity of the hypertext environment. Forexample, they contend that multiple linksemanating from the same point in a docu-ment may confuse the reader. Their alter-native is to have a single link icon in thematerial (text or graphics) which can bequickly queried via the mouse to show thespecific outgoing links, their names, andtheir destination nodes.” They also pro-pose a construct called a )veb IO implementcontext-dependent link display. Every linkbelongs to one or more webs and is onlyvisible when one of those webs is active. Toview documents with the links that belongto a particular web, a user opens a web andthen opens one or more of its documents.Although other webs may also referencethe document, only the links which weremade in the current web are displayed. Asa result, the user does not have to siftthrough the connections made in manydifferent contexts.

The IntermediGproject?s also studyingways of providing an effective bro\vser fora network that can include hundreds oreven thousands of nodes. The Intermediabrowser has two kinds of displays: a global~nup, which shows the entire hypcrdocu-ment and allows navigation within it; anda local map, which presents a view cen-tered on a single document and displayingits links and nearest neighbors in the web.In addition. a display can show nodes andlinks at several levels of detail. For exam-

pk. ic can show whole documents and thelinks between them, or each link and itsapproximate localion within its docu-ments. (See Figure 8.)

The Intermedia project has a long his-tory, many participants, and a se_riousinstitutional commitment to long-termobjectives. It conducts creative hypertextesperiments and uses the classroom as aproving ground. Although this project issIill in its early’stages, we can expect it tocontribute significantly to the develop-ment of effective cooperative work envi-ronments based on hypertext.

Teh-monkNeptune. Tektronix Neptuneis one hypertext system that has been par-ticularly designed as an open, layeredarchitecture.” Neptune strongly separatesthe front end, a Smalltalk-based user inter-face, from the back end, a transaction-based server called the Hypertext Abstract.\lachine (HAM). The HAM is a generichypertext model which provides opera-tions for creating, modifying, and access-ing nodes and links. It maintains acomplete version histor!* of each node inthe hyperdocument, and provides rapidaccess to any version of a hyperdocument.It provides distributed access over a com-puter network, synchronization for mul-tiuser access, a complex networkversioning scheme, and transaction-basedcrash recovery_.

The inte-face layer provides severalbrowsers: A graph browser provides a pic-torial view ;lf a subgraph of nodes andlinks; a docanlenl brotc,ser supports thebrowsing of h ierarchica l s t ructures ofnodes and links; and a node browseraccesses an individual node in a hyper-document. Other browsers include oftrib-ure browsers, version browsers, nodedij/erences browsers, and d e m o nbrowsers. (See Figure 9.)

In Neptune, each end of a link has anoiiset within its node, whether that nodeis textual or graphical. l The link attach-ment may refer to a particular version ofa node, or it may refer to.the current ver-sion. The HAM provides IWO mechanismsthat are useful for building applicationlayers: Nodes and links may have anun!imited number ofattribute/value pairs;ar,d special high-speed predicates areincluded for querying the values of theseprjrs in theentire hyperdocument, allo\\-

29

j%specks =(1859)-

Contemporary Thought:Oarkin’s On tie Origin

of *ties by Means ofNatural Sekchfl, o f t i ePreservation o f FavouredRaces in-tie Sruggk for We<made several points thal hat Imajor Impact onnlnetrenlh-century lhoupht

(1) That biOlOQlCal typesor species do not have a ked,Slatit existence but edsl inpermzmcnt states ol c h a n g eand rlbq

Figure 8. The Intermedia System. This figure illustrates materials from an Infermedia corpus catled “Bio 106: Cell Biology inConlexl.” Three folder windows containing hierarchically organized documents of different types are open in fhc upper leftside of the display. An IntcrText document (lower let1 side) and an InterVal document (upper right side) are currently open, aswell as an IntcrDraw documcnl containing a scanned electronmicrograph (lower middle). This image has been linked to a cor-responding three-dimensional image displayed in an InterSpect document (lower right). The “lower tracking map” (center)shows the links emanaling from the current document. Authors or browsers can manipulate the three-dimensional imnge, editlexl and graphics, follow links or create links at any time in this environmenf. (The electronmicrograph of Micromonas waspublished in the Joltrnol oJPhycology and is reprinted with the permission of the Editor.)

ing higher level applications 10 define theirown accessing mechanisms on the graph.The HAM also provides a demon mecha-nism chat invokes arbitrary code when aspecific HAM event occurs.

diSes.w’s Boxer. Boxer” is a highlyinteracIive programming languagespecif-icall! tailored IO be easy for noncomputcrspecialists co learn. Boxer uses a box torcpresenr a unit of information in the sys-tem. In Boxer, one box cm contain other

- boxes, or data such as ICXI or graphics. For

30

example, a program is a box that containssome boxes that provide input and outputvariables, and other b&es that specifybehavior. The system also supports alter-nate views of some boxes: A box whichspecifies a graphics routine can also showthat graphic display.

Since Boxer is a programming language,it Ire315 cross-reference links in a specialtvay. Rather than using mousable icons aslinks, Boxer uses a specialized box, calleda “por t , ” \vhich giws a direct view imo rhcdesrination. For example, a port from box

A to box B appears within A as a boswhichsh6ws B. But a port is more thanjust a view of rhe destination box, becausethe destination box can be changedthrough any of the porls which lead to it,and the changes willbe reflected in all ofthese ports.

Hicrsrchy is more nalurally expressed inBoxer than in many of the o:her hypertextsystems. Boxes are nested within eachother Iwo-dimensionally. and arc fillcrcd10 reduce rhc level of clutter on the screen.This system oi representation has the

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several Wtems. lncludlng Augment, XanadNeV-unc+md and the Oectronlc Document Syste

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contents of a node to text. In general the content of aObject-Oriented HypenIJCdla System and Clgplicationr Framework.

can be tikrtrary dlgltal data whose Interpretadon may )ncProc. KM OOPSLA’86, (Nov 1986) 186-201.

or digked speech.[NclKl~~~ Nelson, T.H. Mrrory Mathfnrs.T.H. Nelson. SwarKhmore. PA.. 1981.

CRMN11 I Robertson. C., McOacken. 0. and Newell, A. The 2OC approach toman-machlne communication.

lnrrrnoclonol)ournolof Mon-Uocblnt StudIts. 1 4 , 461-488. 1981.

Figure 9. Neptune browsers. Three browsers from Neptune are illustrated. A pictorial view of a network of nodes and links isshown in the Graph Browser (the upper window). The lower righf window and the lower pane of the Document Browser arcviewers for lest nodes. Icons reprcscnfing link affachmrnfs are shown embedded wifhin fhc fexf in each of fhe nodes.

advantage of showing a natural hierarchyof nodes: The windows of lower-levelnodes are nested directly within their par-ents. In;most hypertext systems, noattempt is made to display the parent-childrelationship once the nodes are opened aswindows.

Pirman’s CREF. The Cross-ReferencedEditing Facility (CREF) is a prototype ofa specialized text and graphics editorwhich was developed originally as a toolfor use in analyzing the transcripts frompsychological cspcrimcnts (known aspro-rocols), but which was also used to inves-

September 1987

tigate more general hypertext designissues. I9 Much of the interactive feel ofCREF reflects the style of use and pro-gramming of the Symbol& Lisp machine,on which it was built. Chunks of text.called segments, constitute the nodes in thesystem. Segments are arranged in linearseries, and can have key\vords and variouskinds of links to other segments. Thenotion of a linear set of segments is naru-ral to the protocol analysis problem, sincethe first srcp with such protocols is to seg-mcnt them into the cpisodcs of the cxpcr-imcntal sess ion .

CREF organizes segments into co//ec-

/ions, which can be defined implicitly b)a predicate (called an absrracr collenion)or explicitly by a list (called a sroric collec-lion). At any rime, the selectedcollectiijhappears as a continuous length of text withthe segment boundaries marked by namedhorizontal lines (such as “Segment 1,”“Segment 2.” etc.). This view can beedited as if it were a sin& document.

One way of forming an abstract collec-tion is by selecting segments using aboolean predicate over keywords. Tocslcntl lhc power of this keyword f;icilily.CREF allows the user to dcrinc a type hicr-archy on the keywords. For example, if

31

.

“card 105” is defined as a type of (i.e., achildof) “card,” then collections based onthe keyword “card” will also contain seg-ments which have only “card 105” as akeyword.

CREF supports four kinds of links:rejerences links cross-reference amongsegments; summarizes links impose hier-archy (a summary is a segment which hasone or more summarizes links to other segnents); supersedes links implement ver-sioning by copying the superseded segmentand freezing it; and precedes links riace alinear ordering on segments.

Finally, CREF allows multiple analyststo compose different 0zeorierabout a pro-tocol, using the same segmented data.Each theory imposts its own structure onthe data, and has its own collections, dia-grams, keywords, and annotations. Thismode of selection is similar to the notionof contexts or webs used in other systems.

Hyperfexl on rhe Mucintosh. At leasttwo programs have been written for theApple Macintosh that provide hypertextfacilities: FileVision and Guide.

File\‘ision is primarily oriented tographics nodes and to applications whichcan exploit visual indexing. The advertis-ing for FileVision describes applicationsthat encourage visual indexing. For exam-ple, in the database for a travel agency, themap of a region may contain icons for themain-cities in that region. The user clickson the icon for a city to obtain a display ofa map of that city. The map of the city mayhave icons for the major landmarks in thecity. The user clicks on one of these iconsto obtain a display of data about the land-mark, or perhaps even to obtain a pictureof the landmark itself.

Guide is a more recent program whichis based on an earlier Unix version devel-oped in England.” It does not provide thegraphics capabilities of FileVision(graphics are supported but cannot con-tain links), but it does support textual’hypertext data very well. Guide uses threekinds of links: replacemenl /inks, whichcause the text in the current window to becompletely rep&d by the text pointed toby the link; note links, which display thedestination text in a pop-up window; andreference links, which bring up a ne\y win-dow with the destination text. Guide isnow available for PCs as well.

As this article goes to press, there is newsthat Apple will soon have its own hyper-text system, called HypcrCards. Hyper-Cards will bc similar in some ways toXerox PARC’S NotcCards. It will provide

32

special support for txewablr links. whichwill give it the flavor of a programminglanguage. HyperCards will be bundledwith the system software in new Macin-toshes.

MCC’s PlaneText. PlaneText, devcl-oped in the MCC Software TechnologyProgram (STP), is a very recent additionto the family of general hypertext sys-tems. l PlaneText is based on the Unix filesystem and the Sun SunView windowmanager. Each node is a Unix file. Linksappear as names in curly brackets (I})whose display can be turned on and off.Links are implemented as pointers savedin separate files, so that the linked filesthemselves are not changed by creatinghypertext references between them. Thisdesign allows for the smooth integrationof hypertext into the rest of the Unix-basedcomputational environment, includingsuch tools as Mail and News. It allows forthe hypertext annotation of standardsource code files. In addition, the Unix filedirectory system serves as a “free” mech-anism for creating hierarchical structuresamong nodes. l *

PlaneText supports color graphicsnodes which can be freely linked into ahyperdocument.

Summary. The systems in this sectionwere presented in terms of four broad cat-egories: macro literary systems, problemexploration systems, structured browsingsystems, and general hypertext technol-ogy. Table 1 summarizes this discussionand provides a breakdown of the variousfeatures which current hypertext systems

can include.One additional area of research cur-

rently is the development of systems whichaid the entire process of design, particu-larly the informal upstream aspects. Suchsystems require the features of hypertextproblem exploration and structuredbrowsing systems as well as the advanced

-11 is perhaps loo early IO say. however . howP4rneTc.u will rank in Ihe world of hypcrlexl, since ;Iwill only be publicly available rrom the pjrlicipanl

companies in the hICC;Sof~warc Technology Pro-gram. For mote informalion call Bill SwLcrbcry xhlCC. (512) 343-097s.

‘7hc use of an existing Ircc-slruc!uring mechanismlimits any hypwexl sy$lcm IO only being able IO ban-dlc J single hwarchical vrwurc. Single hicrarrhisalorganirnllonr may be too limucd for some advancedapplicalions.

. .

features of the experimental hypertexttechnologies. Indeed, this area of invcsti-gation may become an important fifth cat-egory for hypertext systems of the future.

The history of hypertext presented heresuggests that the concept and the advan-tages of hypertext were clear severaldecades ago, but that widespread interestin hypertext was delayed until the support-ing technology was cheap and readilyavailable. This suggestion may be mislead-ing. Many of the “elders” of the field feelthat something else has changed as well.They feel that today computer users eas-ily accept the role of the computer as a toolfor processing ideas, words, and symbols(in addition lo numbers and mere data),and as a vchiclc of intcrhuman communi-cation. Those theorists who gave presen-tations of their hypertext systems 20 yearsago, using expensive state of the art hard-ware, report that the computer sciencecommunity showed little interest. Thislack of interest seemed to stem as muchfrom a lack of understanding of the basicconcepts of hypertext as from a lack ofhardware resources.

If this is so, then the recent upsurge ininterest in hypertext may signal that thecomputer community is now ready IO con-sider its technology as much a tool forcommunication and augmenting thehuman intellect as for analysis and infor-mation processing. Hypertext is certainlya large step in that direction.

The Essence ofHypertext

It is tempting to describe the essence ofhypertext as its ability to perform high-speed, branching transactions on textualchunks. But this is a little like describingthe essence of a great meal by listing itsingredients. Perhaps a better descriptionwould focus on hypertext as a computer-based medium for thinking and commu-nica t ion .

- The tinking process does not build new-ideas one at a time, starting with nothing

and turning out each idea as a finishedpearl. Thinking seems rather to proceed onseveral fronts at one, developing andrejecting ideas at different lcvcls and ondifferent points in parallel, each ideadepending on and contributing to theothers.

The recording and communication ofsuch cntwir!cd lines of thought is challcng-ing because communication is in practice

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,processing. Spoken communication ofparallel themes must mark items withstresses, pauses, and intonations which thelistener must remember as the speakerdevelops other lines of argument. Graphi-cal forms can use lists, figures, and tables

‘to present ideas in a less than strictly lin-ear form. These visual props allow thereader/viewer to monitor the items whichhe must understand together. One of thechallenges of good writing, especially goodtechnical writing, is to present several par-allel lines of a story or an argument in away that weaves them together coherently.

Traditional flat text binds us to writingand reading paragraphs in a mostly linearsuccession. There arc tricks for signaIlingbranching in the flow of thought whennecessary: Parenthetical comments, foot-notes, intersectional references (such as“see Chapter 4”), bibliographic refer-ences, and sidebars all allow the author to

say “here is a related thought, in case youare interested.” There arealso many rhe-torical devices for indicating that ideasbelong together as a set but are beingpresented in linear sequence. But these arerough rools at best, and often do not pro-vide the degree of precision or the speedand convenience of access that we wouldlike.

Hypertext allows and even encouragesthe wrirer to make such references, andallows the readers to make their own deci-sions about which links to follow and inwhat order. In this sense, hypertext easesthe restrictions on the thinker and writer.It dots not force a strict decision aboutwhether any given idea is either within theflow of a paper’s stream of thought or out-side of it. Hypertext also allows annota-tions on a text to be saved separately fromthe reference document, yet still be tightlybound to the referent. In this sense, the“linked-ness” of hypertext provides muchof its power: It is the machine processiblelinks which extend the text beyond the sin-gle dimension of linear flow.

At the same time, some applicationsdemonstrate that the “node-ness” ofhypertext is also very powerful. Particu-lariy when hypertext is used as a thinking,writing, or design tool, a natural cor-respondence can emerge between theobjects in the world and the nodes in thehypertext database. By taking advantageof this object-oriented aspect, a hypertextuser can build flexible networks whichmodel his problem (or solution). In thisapplication the links arc less important

September I987

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than the nodes. The links form the “glue”that holds the nodes together, but theemphasis is on the contents of the nodes.

From a computer science viewpoint, theessence of hypertext is precisely that it is ahybrid that cuts across traditional bound-aries. Hypertext is a durubuse mqthod,providing a novel way of directly access-ir,g data. This method is quite differentfrom the traditional use of queries. At thesame time, hypertext is a represenfalionscheme, a kind of semantic network whichmixes informal textual material with moreformal and mechanized operations andprocesses. Finally, hypertext is an inrerfucemod&y that features “control buttons”(link icons) which can be arbitrarilyembedded within the content material bythe user. These are not separate applica-tions of hypertext: They arc metaphors fora functionality that is an essential union ofall three.

The power of linking. In the next twosections of this article, I will explore linksand nodes in more detail as the basic build-ing blocks of hypertext.

Linkjollowing. The most distinguishingcharacteristic of hypertext is its machinesupport for the tracing of references. Butwhat qualif::s a particular reference-tracing device as a link? How much effortis permissible on the part of a user who isattempting to trace a reference? Theaccepted lower limit of refcrcncing sup-port can be specified as follows: To qualifyas hypertext, a system should require nomore than a couple of keystrokes (ormouse movements) from the user to followa single link. In other words, the interfacemust provide links which act like “magicbuttons” to transport the user quickly andeasily to a new place in the hyper-document.

Another essential characteristic ofhypertext is the speed with which th+sys-tern responds to referencing requests. Onlythe briefest delay should occur (one or twoseconds at most). Much design work goesinto this feature in most systems. One rea-son for this concern is that the reader oftendoes not know if he wants to pursue a linkreference until he has had a cursory lookat the referenced node. If making thisjudgement takes too long, the user maybecome frustrated and not bother with thehypertext links.

“.

However, not all link traversals can beinstantaneous. Perhaps as important asrapid response is providing cues to the userabout the possible delay that a given queryor traversal might entail. For example,some visual feature of the link icon couldindicate whether the destination node is inmemory, on the disk, somewhere else onthe network, or archived off line.

Properties oJlinks. Links can be usedfor several functions. These include thefollowing:

l They can connect a document refcr-encc IO the document itself.

l They can connect a comment or anno-tation to the text about which it is written.

l They can provide organizationalinformation (for instance, establish therelationship between two pieces of text orbetween a table of contents entry and itssection).

l They can connect two successivepieces of text, or a piece of text and all ofits immediate successors.

l They can connect entries in a table orfigure to longer descriptions, or to othertables or figures.

Links can have names and types. Theycan have a rich set of properties. Some sys-tems allow the display of links to be turnedon and off (that is, removed from the dis-play so that the document appears as ordi-nary text).

The introduction of links into a text sys-tem means that an additional set ofmechanisms must be added for creatingnew links, deleting links, l changing linknames or attributes, listing links, CIC.

Rejerentiul links. There are twomethods for explicitly linking two pointsin hypertext-by reference and by organ-ization. The reference method is a nonhi-erarchical method. It uses referential linksthat connect points or regions in the text.

Referential links are the kind of link thatmost clearly distinguishes hypertext. Theygenerally have two ends, and are usuallydirected, although most systems support“backward” movement along the link.The origination of the link is called the“link source,” and usually acts as therejerence. The source can logically beeither a single point or a region of tesl. Atthe other end. the “destination” ofrhc linkusually functions as the rejpren/, and can

‘Link dclction is problematical. For example. whatshould the policy be lo: nodes which art slrandcdwhen all their links have been dclcwd? Should they beplaced in “node limbo” umil the user dcudcs u t3l IOdo with them?

33

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Figure 10. An example of a link with a point source and a region destination. Thesource of the link is a token in the lext of document A which contains a textualidentifier (“xxxx”). The identifier may be (1) the name of the destination node (inthis case it would be “B”), (2) the name of the link, or (3) an arbitrary string whichis neither the name of the link nor the destination node. The destination of this linkis node B which is a region. The link has an internal name (5327) which is normallyvisible to the user.

also be either a point or a region. (See Fig-ure 10.)

A linkpoint is some icon indicating thepresence of the link. It usually shows thelink’s name and perhaps also its type. Orit may show the name and/or type of thedestination node. In systemssuch asNep-tune which support links with both pointsource and point destination, the icon alsoindicates which type of linb is indicated, Insome systems, the display of links can besupprcsscd. so that the documents appearlinear.

A fink region is a set of contiguouscharacters which is displayed as a singleunit. In Figure 10, the link destination isa link region, namely, an entire node. Fig-

34

ure 10 illustrates the most common formof hypertext link, in which the source is apoint and the destination is a region. Thisexample typifies many of the link applica-tions listed above, because it shows how a

-chunk of text-a region-is written about%r referenced by some smaller chunk oftext, often a sentence. Since most readersare accustomed to single point referencesto sentences (i.e., footnotes), they have noproblem accepting a link with a pointsource. There can be regions in graphics aswell-either bordered regions or collcc-Cons of graphic objecrs in a figure.

Link regions can pose difficult designproblems. They arc casiesl to implemcnr

as whole nodes. since setting a region OTT

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from its neighboring material within thesame node raises a tough implementationissue-how lo display the selected regionto the user. It must be highlighted some-how, using reverse video, fonts, or color,but each of these options poses difficultiesin keeping overlapping regions clearlyhighlighted. The Intermedia designers pro-pose to draw a light box around regionsand a darker box around region/regionoverlaps, thus shoying a single level ofoverlapping”; however, this technique isnot effective if there are more than twooverlapping regions.

Another difficulty posed by link regionsis how to show the name of the link. Unlikea link point, a link region has no obviousposition for a title, unless it is placedarbitrarily at the beginning oi end of theregion.

Link regions can also be difficult tomanipulate. Designers must devise a sys-tem for copying, moving, modifying, anddeleting the region and the substringswithin it. The movement of regionsinvolves logistical dilemmas which are noteasy to resolve: For example, when onemoves a major portion of the text in a des-tination region lo someplace else in thenode, should the link destination movewith it or stay with what remains? Also,designers must make special provisions fordeleting, moving, or copying the definingend points of a region.

Organizational links. Like referencelinks, organizational links establishexplicit links between points in hypertext.Organizational links differ from rcferen-lial links in that lhcy implcmcnt hicr;lrchi-cal information.

Organizational links connect a parentnode with‘ its children and thus form astrict tree subgraph within the hypertextnetwork graph. They correspond to the IS-A (or superconcept) links of semantic nettheory, and thus operate quite differentlythan referential links.’ For example,rather than appearing as explicit high-lighted tokens in each node, organiza-tional links are often traversed by aseparate mechanism at the node controllevel (i.e., special goto-parent, goro-jifst-child, and golo-nexl-sibling commands).In other cases, there are organizationalnodes (such as tot nodes in Tcxtner andFilcBoses in NotcCards) which record theorganizational structure.

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Keyword l inks. In addition to theexplicit linking performed by referentialand organizational links, there is a kind ofimplicit linking that occurs through the useof keywords. This type of linking is yet tobe fully explored.

One of the chief advantages of text stor-age on a computer is the ability to searchlarge and complex documents and sets ofdocuments for substrings and key-words. l Naturally, this ability is also avaluable aspect of hypertext. Indeed, mostusers of large hyperdocuments insist onhaving some mechanism for scanning theircontent, either for selected keywords(which can apply to nodes, links, orregions) or for arbitrary embedded strings.

From a funcIiona1 standpoint, link fol-lowing and search are similar: Each is away to access destination nodes that are ofpossible interest. Link following usuallyyields a single node, whereas search canyield many; hence, a keyword is a kind ofimplicit computed link. The value of thisinsight is that it may allow design of ahypertext interface which is consistentacross all link-tracing activities.

To tree or nor to Iree. Some hypertextsystems (for example, Emacs INFO) sup-port only hierarchical structures, others(such as Xanadu and Hyperties) provideno specificsupport for hierarchical struc-tures, and others (such as Textnet andNoIeCardsj support both kinds ofstruclures.

One could question just how sufficientstrictly hierarchical structures are, and forwhich applications they are sufficient andfor which they are not. On the one hand,abstraction is a fundamental cognitiveprocess, and hierarchical structures are themost natural structures for organizinglevels of abstraction. On the other hand,cases obviously exist where cross-hierarchical links are required. FrankHalasz, one of the developers ofNoteCards, has gathered statistics on thehypefspuce of a single representativeNoteCards user; this person had 1577nodes (cards) in all, 502 of whi& were File-Boxes (hierarchical nodes). Connectingthese nodes were a total of 3460 links, 2521

7hcrc 1s some con~r~verry owr Ihc rela~ivc mcriu ofkcy\vord reuieval PS opposed IO full WI search. On theone hand, keyword rclricval is only as good as Ihe skilland lhoroughncss of Ihe person sclwing Ihe key-words. On Ihe olhcr hand. full 1~x1 search does no1find all the rclcvan\ documcnls. nor does ir always findonly~hcrclcvan~documcncs. Ilrshor~omingsarcducin par* 10 fhc commonness Of synotlyms in English. InaddIllon, full ICX~ search can be compulalionally pro-hibuisc in large nelworks.

Seprember 1967

(73 percent) of which connected FileBoxesto each other or to individual notecards,261 (7.5 percent) of which were nonhier-archical referential links, and theremainder of which were mail links (usedby the system to tic mail messages to othernodes). This example, for what if is worth,suggests that hierarchical structure is veryimportant in organizing a hypertext net-work, and that referential links are impor-tant but less common.

One advantage of a strictly tree-orientedsystem is that the command language fornavigation is very simple: From any node,the most one can do is go to the parent, asibling, or a child. This simplicity alsodiminishes the disorientation problem,since a simpler cognitive model of theinformation space will suffice.

Of course, the great disadvantage of anyhierarchy is that its structure is a functionof the few specific criteria thaI were usedin creating it. For example, if one wishesto investigate what sea-based life formshave in common with land-based lifeforms, one may find that the traditionalclassification of life forms into the plantand animal kingdoms breaks up the infor-mation in the wrong way. The creator ofa hierarchical organization must anticipatethe most important crireria for later accessto the information. One solution to thisdilemma is to allow the informaIion ele-mcnIs IO be sIrucIured into mulIiple hier-archies, thus allowing the world IO be“sliced up” into several orthogonaldecompositions. Any hypertext systemwhich has hierarchy nodes, such as Text-net (tot nodes) and NoteCards (FileBoxnodes), can perform this operation quiteeasily. These are the only systems whichexplicitly claim to support multiple hierar-chies. Indeed, one early user of NoteCardsused the system in doing the research andwriting for a major project paper; heimposed one organization on the data andhis writings while doing the research, andthen quite a differenr (yer coexistent)organization on the same maIerial IO pro-duce his paper. As a generalization, itseems thar engineering-orienIcd hypcrIextusers prefer hierarchical organizations,whereas arts- or humanities-oriented usersprefer cross-referencing 0rganizaIions.

Euetlsions IO basic links. CerIain fea-tures of the link enable it to be extended in

several ways. Links can connect more thantwo nodes to form clusterlinks. Such clus-ter links can be useful for referring toseveral annotations with a single link, andfor providing specialized organizationalstructures among nodes. Indeed, the totnodes of Textnet and the FileBoxes ofNoteCards are both forms of clusIer links.

One useful way to extend the basic linkis to place attribute/value pairs on linksand IO query the network for them. TheNeptune system, for example, has anarchitecture that is optimized for this func-tion. Coupled with specialized routines inthe daIabase interpreter (the HA1\1), theseaIIribute lists allow users to customizelinks in several ways, including devisingtheir own type system for links and per-forming high-speed queries on the types.

It is also possible to perform proceduralattachments on alink so that traversing thelink also performs some user-specified sideeffect, such as customizing the appearanceof the destination node. This ability isprovided in Neptune and Boxer.

Hypertext nodes. Although the essenceof hypertext is its machine-supponed link-ing, the nodes contribute significantly IO

defining the operations that a hyperrextsystem can perform. Most users of hyper-text favor using nodes which express a sin-gle concept or idea, and are thus muchsmaller than traditional files. When nodesare used in Ihis fashion, hypcrIcxIintroduces an intermediate level ofmachine support between characrers andfiles, a level which has the vaguely seman-tic aspect of being oricnIcd IO the cxprcs-sion of ideas. Bur this sizing is compleIelyar the discretion of the hypertext writer,and Ihe process of determining how tomodularize a document into nodes is anart, because its impact on the reader is notwell understood.”

The rnodulorizotion ofideos. Hb-pertextinvites the writer to modularize ideas intounits in a way IhaI allows (1) an individualidea to be referenced elsewhere, and (2)alrernative Successors of a unir IO b eoffered to the reader (for instance, moredetail, an example, bibliographic refer-ences, or the logical successor). But thewriter must also reckon \viIh the fact IhaIa hypcrIexI node, unlike a texIua1 para-graph, tends to be a stricr unit which doesnot blend seamlessly with its neighbors.Some hypertext systems (Norecards,CREF, Boxer. FRES, NLS) nllow nodrs IObe viewed Iogether as if they were one bignode, and this op:ion is essential for some

35

applications (for example, writing and.reading prose). But the boundaries aroundnodes are always discrete and requiresometimes difficult judgcments about how10 cleave the subject matter into suitablechunks.

The process of identifying a semanti-cally based unit, such as an idea or con-cept, with a syntactic unit, such as aparagraph or hypertext node, is not uniqueto hypertext. Manuals of style notwith-standing, traditional text has rather looseconventions for modularizing text intoparagraphs. This looseness is acceptablebecause paragraph boundaries have a rela-tively minor effect on the flow of the read-ing. Paragraph boundaries are sometimesprovided just IO break up the text and givethe eye a reference point. Thus, decisionsabout the distribution of sentences amongparagraphs is not always critical.

Hypertext, on the other hand, canenforce a rather stern information hiding.In some systems, the only clue a user hasas to the contenrs of a destination node isthe name of the link (or the name of thenode, if that is provided instead). Thewriter is no longer making all the decisionsabout the flow of the text. The reader canand must constantly decide which links IOpursue. In this sense, hypertext imposes onboth the writer and the reader the need formore process awareness, since either onehas the option of branching in the flow ofthe text. Thus hypertext is best suited forapplicarions which require these kinds ofjudgcments an)-way, and hypcrlcxt mcrclyoffers a way 10 act directly on these judge-menrs and see [he results quickly andgraphically.

ldeosus objects. While difficult to docu-ment, there is something very compellingabout reifying the expression ofideas intodiscrete objects [o be linked, moved, andchanged as independent entities. Alan Ka)and Adele Goldberg” observed ofSmall[alk that ir is able to give objects aperceptual dimension by allocating tothem a rectangular piece of screen realestate. This feature offers enhancedretrieval and recognition over computer-processed flat documents, because 10 amuch greater degree abstract objects aredirectly associated with perceptualobjects --rhe windows and icons on thescreen.

Paragraphs, sections. and chaprers in abook, viewed through a standard text edi-tor or word processor, don’t stand out asfirst-class entities. This is particularlyapparent when one can view one’s docu-

36

-

ment hierarchically (i.e., as an outline) atthe same time that one adds new sectionsand embellishes existing ones. Peopledon? think in terms of “screenfulls”; theythink in terms of ideas, facts, and evi-dence. Hypertext, via the notion of nodesas individual expressions of ideas, providea vehicle which respects this way of think-ing and working.

Typed nodes. Some hypertext systemssort nodes into different types. Theselypednodes can be extremely useful, par-ticularly if one is considering giving themsome internal structure, since the types canbe used IO differentiate the various struc-tural forms.

For example, in our research in theMCCSoftwareTechnologyProgram,wehave been implementing a hypertext inter-face for a design environment called theDesign Journal. The Design Journal isintended 10 provide an active scratchpadin which the designer can deli5erate aboutdesign decisions and rationale, bothindividually and in on-line design meet-ings, and in which he can integrate thedesign itself with this less formal kind ofinformation. For lhis purpose we haveprovided a set of four typed nodes for thedesigner to use-noles, goals/consfrainrs,ani/octs, and decisions. Nofes arc used forcvcrything from reminders, such as “AskBill for advice on Module X,” to specificproblems and ideas relating 10 the design.Goals/constraints are for the initialrequirements as well as discovered con-straints within the design. Artifacts are forthe elements of the output: The Design.And decisions are for capturing the branchpoints in the design process, the alterna-tives considered by the designer, and someof the rationale for any commitment (how-ever remalive) that has been made. Thedesigner captures assumptions in [he formof decisions with only one alternative. Ourprototype of the Design Journal uses colorto distinguish between note types in thebrowser, and we have found this to be avery effective interface.

Hypertext systems that use typed nodesgenerally provide a specialized color, size.or iconic form for each node type. The dis-

tinguishing fearures help the user differen-tiate at a glance rhe broad classes of typednodes that he is working wirh. Systemssuch as NoteCards, Intermedia, and IBISmake cstensivc USC of typed nodes.

,. :.Scntisrrrr&reti Nodes.’ So far I have

‘spoken of the hypertext node as a struc-tureless “blank slate” into which onemight put a word or a whole document.For some applications, there is growinginteresr in semistrucfured nodes-typednodes which contain labelled fields andspaces for field values. The purpose ofproviding a template for node contents isto assist the user in being complete and IOassist the computer in processing thenodes. The less that ihecontent of a nodeis undifferentiated natural language (forexample, English) text, the more likely thatthe computer can do some kinds of limitedprocessing and inference on the textualsubchunks. This notion is closely relatedto Malone’s notion of semistructuredinformat ion sys tems.” ~

To continue wirh the example of theDesign Journal, we have developed amodel for the internal structure of deci-sions. The model is named ISAAC. Itassumes that therearc four major compo-nents 10 a design decision:

(1) an issue. including a short namefor the issue and a short paragraphdescribing it in general terms;(2) a set of olfernarives, each of whichresolves the issue in a different way,each having a name and shortdescription, and each potentiallylinked to the design documents or ele-ments that implement the alternative;(3) an analysis of the competing alter-natives, including the specific criteriabeing used IO evaluate them, rhetrade-off analysis among these alter-natives, and links to any data that theanalysis diaws upon; and(4) a commifmenf IO one of the alter-natives (however tentatively) or co avector of preferences over the alter-natives, and a subjective rating aboutthe correctness or confidence of thiscommitment.

Without getting into the details of theunderlying theory, I merely wish 10 stresshere that the internal structure of ISAACsuggests that the author of an IStiC deci-sion is engaged in a+ch more structuredactivity than just “writing down the deci-sion,” and the reader is likewise guided bythe regularity of the ISAAC structure.

Of course, it may not be clear why \ve donot treat each of [hc elements lisred aboveas its own typed hypertest node. The rea-son is that the parts of an ISAAC frameare much more rightly bound logetherthan ISAAC frames are bound IO eachother. For example, we could not have an

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analysis part without an alternatives part;yet if we treat them as separate hypertextnodes, we have failed to build this con-straint into the structure. The general issuehere is that some information elemeqts One problem with composite nodes ismust always occur together, while others that as the member nodes grow and changemay occur together or not, depending on the aggregation can become misleading orhow related they are in a given context and incorrect. A user who encounters thishow important it is to present them as a problem is in the same predicament as acluster distinct from “surrounding” infor- writer who has rewritten a section of amation elements. This problem is recur- paper so thoroughly that the section titlesiVe: /.n element that is atomic at one level is no longer accurate. This “semanticmay turn Out on closer inspection to con- drift” can be difficult to catch.lain many components, some of which areclustered together. Analog\’ to semantic networks. The idea

In hypertext this tension presents itself of building a directed graph of informalas the twin notions of scmistructurcd textual elements is similar lo the Al con-nodes and composite nodes. cept of semonlic nerbvofks. A semantic

Composite nodes. Another mechanism network is a knowledge representalion

for aggregating related information in scheme consisting of a directed graph in

hypertext is the composife node. Several which concepts are represented as nodes,

related hypertext nodes are “glued” and the relationships between concepts are

together and the collection is treated as a represented as the links between them.

single node, with its own name, types, ver- What distinguishes a semamic network as

sions, etc. Composite nodes are most use- an AI representation scheme is fhat con-

ful for situations in which the separate cepts in the representation are indexed by

items in a bulleted list or the entries in a their semantic content rather than by some

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-

table). This practice can, however, under- works is that they are natural to use, since

mine the fundamental association of one related concepts tend to cluster together in

interface object (window) per database the network. Similarly, an incompletely or

object (node), and rhus must be managed inconsistently defined concept is easy to

well to avoid complicating the hypertext spot since a meaningful context is provided

idiom unduly. by those neighboring concepts IO which itA composite node facility allows a is alreadY linked.

group of nodes to be treated as a single The analogy to hypertext is straightfor-node. The composite node can be moved ward: Hypertext nodes can be thought ofand resized. and closes up to a suitable icon as representing single concepts or ideas,

reflecting its contents. The subnodes are internode links as representing the seman-

separable and rearrangeable through a tic interdependencies among these ideas,

subedit mode. The most flexible means of and the process of building a hypertext net-

displaying a composite node is to use a work as a kind of informal knowledge

constraint language (such as that devel- engineering. The difference is that Al

oped by Symbolics for Constraint Frames) knowledge engineers are usually striving to

which describes the subnodes as panes in build representations which can be

the composite node window and specifies mechanically interpreted, whereas the goal

the interpane relationships as dynamic of the hypertext writer is often to capture

constraints on size and configuration. an interwoven collection of ideas without

Composite nodes can be an effective regarda their-machine interpretability.

means of managing the problem of having The work on semantic networks also sug-

a large number of named objects in one’s gests some natural extensions to hypertext,

environment. Pirman described the prob- such as typed nodes, semistructured nodes

lem this way: (frames), and inheritance hierarchies of

In this sari of system. there is a never-ending node and link types.tension bctwecn trying 10 name everything (inwhich case, the number of named lhings cangrow quickly and rhescr can become quicklyunmanageable) or to name as little as Dossi- The advantages andblc (in wvilich cm, ~hmgs thn! look J iot oftrouble to COIISI~UCI can bc I~rd IO rctricvcif one acciden[ally drops the poinrers [Orhem).lY

uses of hype&t

Interrextual references are not new. The

importance of hypenelt is simply thatreferences are machine-supported. Likehyperlext, traditional literature is richlyinterlinked and is hierarchically organircd.In traditional literature. the medium ofprint for the most part resfricts the flow ofreading IO folicw the tlow of linearlyarranged passages. However, the processof following side links is iundamental evenin the mediumof print. In fact, library andinformation science consist principally ofthe investigation of side links. Anyonewho has done research knows that a con-siderable portion of that effort lies inobtaining referenced works, looking upcross-references, looking up ccrms in a dic-tionary or glossary, checking tables andfigures, and making noles on notecards.Even in simple reading one is constantl)negotiating references to other chapters orsections (via the table of contents or refer-ences embedded in the test), index entries,footnotes, bibliographic references, side-bars, figures, and tables. Often a textinvites the reader to skip a section if he isnot interested in greater technical detail.

But there are problems with the rradi-tional methods.

l Most references can? be traced back-wards: A reader can nor easily find wherea specific book or article is referenced ina document, nor can the aurhor of a paperfind out who has referenced the paper.

l As the rcadcr winds his way down vnr-ious refercncc trails, he must keep track ofwhich documents he has visited and whichhe is done with.

l The rcadcr must squeeze annotationsinto the margins or place rhem in a sepa-rate document.

l Finally, following a referential trailamong paper documents requires subsran-tial physical effort and delays, even if thereader is working at a well-stocked library.If the documents are on linc, the job is eas-ier and faster, but no less tedious.

New possibilities for authoring and design.Hypertext mayoffer new Ilays for authorsand designers to work. Authoring isusually viewed as a word- and sentence-level activity. Clearly the \\ord processor l

37

is a good tool for authoring at this level.However; authoring obviously has muchto do with structuring of ideas, order ofpresentation, and conceptual exploration.Few authors simply sit down and pour outa finished text, and not all editing is just“wordsmithing”and polishing. In a broadsense, authoring is the design o/u docu-menf. The unit of this level of authoring isthe idea or concept, and this level of workcan be effectively supported by hypertext,since the idea can be expressed in a node.As the writer thinks of new ideas, he candevelop them in their own ,lodes, and thenlink them to existing ideas, or leave themisolated if it is loo early to make suchassociations. Thespecialized refinementsof a hypertext environment assist themovement from an unstructured networkto the final polished document.

New possibilities for reading andretrieval. Hypertext may also offer newpossibilities for accessing large or complexinformation sources. A linear (nonhyper-text) document can only be easily read in

-the order in which the text flows in thebook. The essential advantage of non-linear text is the ability to organize text indifferent ways depending on differingviewpoints. Shasha provides the followingdescription of this advantage:

Suppose you are a touris. interested in visit-ing museums in a foreign city. You may beinterested in visual arrs. You may want toseemuseums in your local area. You may onlybc inrcrcstcd in incxpcnsivc muscums. Youccrrainly want 10 make sure the museums youconsider arc open when you want IO visitthem. Now your guidebook may be arrangedby subject, by name of museum, by location.and so on. The rroublc is: if you are inrercstedin any arrangcmcnt other than the one it uses,you may have IO do a lot of searching. Youare not likely IO find all the visual artsmuseums in one secrion of a guidebook thathas been organized by district. You maycarryseveral guidebooks. each organized by acriterion you may be inrcrcsred in. The num-ber of such guidebooks is a measure of theneed for a nonl inear texi system.”

Another advantage is that it is quite nat-ural in a hypertext environment IO suspendreading temporarily along one ,line ofinvestigation while one looks into somedetail, example, or related topic. Bushdescribed an appealing scenario in his 1945article:

The owner of the mcmcs. lcr us say, isinlcrcslcd in the origin and propcrtics of thebow and arrow. Specifically hc is srudyingwhy the shorr Turkish bow was apparentlysuperior IO rhe Enghsh long bow in [he skir-mishes of lhc Crusades. He has dozens ofpossibly pcrlincni books 2nd articles in his

38

, r.*I

mcmex. First he runs through an cncyclopc-dir, finds an interesting but sketchy article.leaves it projected. Next, in a history, he findsanother pertinent hem, and ties the twotogether. Thus he goes, building a trail of

many items. Occasionally he inserts a com-ment of his own. either linking it into themain :rail or joining it by a side trail to a par-ticular item. When it bccomu evident that theelastic properties of available materials hada great deal to do with the bow, he branchesoff on a side trail which takes him throughtextbooks on elasticity and tables of physicalconstants. He inserts a page of longhandanalysis of his own. Thus he builds a (perma-nent] trail of his interest through the maze ofmaterials available IO him.*

As we have seen, Bush’s notion of the“trail” was a feature of Trigs’s Testnet,allowing the hypertext author to establisha mostly linear path through the docu-ment(s). The main (default) trail is wellmarked, and the casual reader can read thetext in that order without troubling withthe side trails.

Summary. We can summarize the opera-tional advantages of hypertext as:

ease of tracing references: machinesupport for link tracing means that allreferences are equally easy to followforward to their referent, or back-ward to their reference;ease of crearing new references: userscan grow their own networks, or sim-ply annotate someone else’s docu-ment with a comment (withoutchanging the referenced document);infortuorion slrucluring: both hierar-chical and nonhierarchical organiza-tions can be imposed on unstructuredinformation; even multiple hierar-chies can organize thesame material;global views: browsers provide table-of-contents style views, supportingeasier restructuring of large or com-plex documents; global and local(node or page) views can be mixedeffectively;cusfouCzed documenrs: text segmentscan-& threaded together in manyways, allowing the same document toserve multiple functions;rnodularily of infornlarion: since thesame test segment can be referencedfrom scverai places. ideas can beexpressed with less overlap and dupli-cation;consislency Of inforn~ofion: rcfer-cnccs arccnlbcddcd in their test. and

if the text is moved, even to anolherdocument, the linkinformation stillprovides direct access to thereference;ruskstucking: the user is supported inhaving several paths of inquiry activeand displayed on the screen at thesame time, such that any given pathcan be unwound to theoriginal task;collaboration: several authors cancollaborate, with the document andcomments about the document beingtightly interwoven (the cxploratio-, ofthis feature has just begun).

The disadvantages ofh y p e r t e x t

There are two classes of problems withhypertext: problems with the currentimplementations and problems that seem10 be endemic to hypertext. The problemsin the first class include delays in the dis-play of referenced material, restrictions onnames and other proper:ies of links, lackof browsers or deficiencies in browsers,etc. The following section outlines twoproblems that are more challenging thanthese implementation shortcomings, andthat may in fact ultimately limit the useful-ness of hypertext: disorientation and cog-

nitive overhead.

Gttling “lost in space.” Along with thepower to organize information much morecomplexly comes the problem of having toknow (1) where you are in the network and(2) how to get to some other place that youknow (or think) exists in the network. I call

this the “disorientation problem.” Ofcourse, one also has a disorientation prob-lem in traditional linear text documents,but in a linear text, the reader has only twooptions: He can search for the desired textearlier in the .tcxt or later in the text.Hypertext offers more degrees of freedom,more dimensions in which one can move,and hence a greater potential for the userto become lost or disoriented. In a ner\vorkof 1000 nodes, information can ea_silybecome hard to find or even forgoTtenaltogether. (See Figure i 1.)

There are two major technological solu-tions for coping with disorientation-graphical browsers and qucry/scarchm e c h a n i s m s . Bro\rscrs rely on theextremely highly developed visuospatialprocessing of the human visual system. Byplacing nodes and links in a two- or thrce-dirncnsionnl spasc, providing them with

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properties useful in visual differentiation(color, size, shape, texture), and maintain-ing cert@n similarities to our physical envi-tinment”(for example, no two objectsoccupy the same space, things only moveif moved, etc.), browser designers are able10 crcaie quite viable virtual spatial envi-ronments. Users orient themselves by vis-ual cuts, just as when fhcy arc walking ordriving through a familiar city. However,the:e is no narural topology for an infor-malion space, except perhaps that higherlcvcl conccprs go a[ rhc top or on the leftside, so until one is familiar with a given

September 1987

large hyperdocument, one is by definitiondisoriented. In addition, an adequate vir-tuality is very difficult IO maintain for alarge or complex hypertext network. Suchparameters as (1) large numbers of nodes,(2) large numbers of links, (3) frequentchanges in the nerwork, (4) slow or awk-ward response to user control inputs, (5)insufficicnr visual diffcrcnriation amongnodes and/or links, and (6) nonvisuallyoriented users combine IO make it pracri-tally impossible IO abolish rhe disoricnta-[ion problem with a browser alone.

One solurion 10 this dilemma is IO apply

standard database search and query tcch-niques to locating the node or nodes whichthe user is seeking. This is usua!J done byusing boolean operations IO apply somecombination of keyword search, full stringsearch, and logical predicates on otherattributes (such as author, time of crea-lion, Iypc, c1c.) of nodes or links. Simi-larly, one can fihcr (or ellide) informaGonso thal the user is presented with a manage-able level of complexity and detail, and canshifr the view o r the dclnil suppressionw h i t e navigafing rhrough ~hc ncf\vork.Howcvcr, much research remains IO bc

39

done on effective and standardizedmethods for eliision.

The cognitive task scheduling problem.The other fundamental problem withusing hypertext is that it is difficult tobecome accustomed to the additional men-tal overhead required to create, name, andkeep track of links. I call this “cogniriveoverhead.” Suppose you are writing aboutX, and a related thought about Ycomes tomind and seems important enough to cap-ture. Ideally, hypertext allows you to sim-ply “press a button” (using some mouseor keyboard action) and a new, emptyhypertext window pops onto the screen.You record Yin this new window, thenyou press another button, the Y windowdisappears, and you are in the Xwindowright where you were when Yoccurred toyou.

Unfortunately, the situation is a bitmore complex than this scenario implies.If Y has just occurred to you, it may stillbe hazy and tentative; the smallest inter-ruption could cause you to lose it. Comingup with a good word or short phrase tosummarize Y may not be easy. You haveto consider not just what is descriptive butalso what will be suggestive for the readerwhen he encounters the link to Ywithin X.In addition, you must determine whetheryou should name the link to Y to suggestthe contents of Yor to show Y’s relation-ship to X. Some systems (for example,NoteCards) provide that links can haveboth a type (such as “idea”) and a label(such as “subsume A in 5”). Coming upwith good names for both can impose evenmore load on an author srruggling with anuncertain point. (One way to reduce thisproblem is for the authoring system IO sup-port immediate recording of the substanceof the idea, deferring the creation andlabeling of the link and/or the node unrilafter the thought has been captured.)

Beyond that, you must also consider ifyou have provided sufficient links to Ybefore returning to work on X. Perhapsthere are better ways to link Y to the net-work of thoughts than at the point in X

_ wher+_Y came to mind.Th? problem of cognitive overhead also

occurs in the process of reading hypertext,which tends to present the reader with alar_ee number of choices about ‘which linksIO follow and which IO lcnvc alone. ThcscClioiccs cngcndcr a certain ovcrhcad ofmelalcvel decision making, an overheadthar is absent when the author has alread)made many of thcsc choices for you. A t

the moment that you cncountcr a link,

40

.

how do you decide if following the sidepath is worth the distraction? Does thelabel appearing in the link tell you enoughto decide? This dilemma could be called“informational myopia.“The problem isthat, even if the system response time isinstantaneous (which it rarely is), youexperience a defmite distraction, a “cog-nitive loading,” when you pause to con-sider whether to pursue theside path. Thisproblem can be eased by (1) having thecross-referenced node appear very rapidly(which is tI-.e approach of KMS), (2)providing an instantaneous one- to three-line explanation of the side reference in apop-up window (which is the approach ofIntermedia), and (3) having a graphicalbrowser which shows the local subnetworkinto which the link lcads.

These problems are not new with hyper-text, nor are they mere byproducts ofcomputer-supported work. People whothink for a living-writers, scientists,artists, designers, etc.-must contend withthe fact that the brain can create ideasfasrcr than the hand can write them or themouth can speak them. There is always abalance between relining thecurrent idea,returning to a previous idea to refine it,and attending to any of the vague “proto-ideas” which are hovering at the edge ofconsciousness. Hypertext simply offers asufficiently sophisticated “pencil” IObegin to engage the richness, variety, andinterrelatedness of creative thought. Thisaspect of hypertext has advantages whenthis richness is needed and drawbackswhen it is not.

To summarize, then, the problems withhypertext are

disorientation: the tendency to loseone’s sense of location and directionin a nonlinear document; andcognitive overheud: the additionaleffort and concentration necessary tomaintain several tasks or trails at onetime.

These problems may be at least partiallyresolvable through improvements in per-formance and interface design of hyper-text systems, and through research oninformation filtering techniques.

n this article, 1 have reviewed exist-ing hypertext systems, the opportu-nities and problems of hypcrtcxt, and

some of the top-level design issues ofbuilding hypertext systems. It has been my

intention to give the reader a clear sense of

what hypertext is, what its strengths andwcakncsscs arc. and what it can bc used

for. But-1 also intended something more:that the reader come away from this rrti-de excited, eager IO try using hypertext forhimself, and aware that he is at the btgin-ning of something big, something like theinvention of the wheel, but something thatstill has enough rough edges that no one isreally sure that it will fulfill its promise.

To that end, I mention one more bookthat might be considered to belong to theliterature on hypertext. Neuromoncer2’ isa novel about a time in the distant futurewhen the ultimate computer interface hasbeen perfected: One simply plugs one’sbrain into the machine and experiences thecomputer data directly as perceptual enti-ties. Other computers look like boxesfloating in three-dimensional space, andpasswords appear as various” kinds ofdoors and locks. The user is completelyimmersed in a virtual world, the “operat-ing system,” and can move around andtake different forms simply by willing it.

This is the ultimate hypertext system.The basic idea of hypertext, after all, isthat ideas correspond to perceptualobjects, and one manipulates ideas andtheir relationships by directly manipulat-ing windows and icons. Current technol-ogy limits the representation of theseobjects to static boxes on a CRT screen,but one can easily predict that advances inanimation, color, 3D displays, sound,etc.-in short, Nelson’s hypermedia-willkeep making the display more active andrealistic, the data reprcsentcd richer andmore detailed, and the input more naturaland direct. Thus, hypcrtcxt, far frombeing an end in itself, is just a crude firststep toward the time when the computer isa direct and powerful extension of thehuman mind, just as Vannevar Bush envi-sioned when he introduced his Mcmexfour decades ago.0

Acknowledgements

I wish IO thank Les Bclady, Bill Curtis. SusanGerhan. Raymondc Cuindon, Eric Gullichscn.Frank Halasz. Peter Marks, and Andy van Damfor their rhoughtful reading of previous drafts.

References1. T.H. Nelson. “Gclting II Our of Our Sys-

(cm.” Injorrfraiio~l Rclrrcvul: 11 CrllrctrlI\‘cv;cw. C. Schcchlcr, c d . . ‘I‘hompronBooks. Wash., D.C., 1967.

2. V. Bush, “As WC Xlny Think.” ,4llanrir,Voonrh/~. July 1945. pp.lOl-109.

3. D.C. Engclbart. “A Conccplual Frnmc-w o r k f o r the Augmcnr~lion or ,Man’s

COMPUTER

I ; . . .. .:more:is arri-y”/! for

.-1e

,;hat*one is*misc.: bookto the:ei’ isfuturecc hasone’s

:es the.I enti-boxes:, andds ofAetely?erat-3 anding it.stem.all, is.ptuals and)ulat-hnol-these

Intcllcct ,” in V&as in In/wmolion Hon-dliq, Vol. I, Spartan Books, London,1963.

4. D.C. Engclbart and W.K. English, “AResearch Center for Augmenting HumanIntellect,” AFIfS Con/. froc.. Vol. 33.Part 1. The Thompson Book Company,WashingI&, D.C.. 1968.

5. T.H. Nelson. “Replacing the PrintedWord: A Complctc LitcrarySystem.“fFJPProc., October 1980, pp. 1013-1023.

6. R.H. Trigg, A Network-basedApproach IO7ex1 Handling jar Ihe Online ScientijicCommunily, PhD. Thesis, University ofMaryland, 1983.

7. H. Rittcl and M. Webbcr, “Dilemmas in aGeneral Theory of Planning,” PO/icySciences, Vol. 4, 1973.

8. D.G. Lowe, “Cooperative Structuring ofI n f o r m a t i o n : The Rcprcscntatio? ofReasoning and Dcbatc,” in In/‘/. 1. ofMon-Machine Sludics,” Vol. 23, 1985, pp.97-111.

9. J.B Smith et al, “WE: A Writing Environ-ment for Professionals,” Technical Report86-025, Department of Computer Science,University of North Carolina at ChapelHill, August 1986.

10. W. Hershey, “Idea Processors,” BYTE.June 1985, p. 337.

:c_ .und,-will: and. andtural‘ramfirst

:cr is* the:nvi-

mex

11. D. McCracken and R.M. Akscyn, “Expe-rience with the ZOG Human-computerInterfaceSystem,” Jnl’lJ. o_fMon-MachineStudies, Vol. 21, 1984, pp. 293-310.

12. B. Shneidcrman and J. Morariu, “TheInteractive Encyclopedia System (TIES),”Department of Computer Science, Univer-sity of Maryland, College Park, MD 20742,June 1986.

13. J.H. Walker. “The Document Examiner.”

14.

IS.

SIGGRAPH’ Video Re,ic.v. Edited Compi-lation from CHI’85: iiumon Fuclors inComputing System, 19F5.F.G. Halasr. T.P. Moran, and T.H. Trigg,“NoteCards in a Nutshell,” Proc. ojrhcACM Con/. on llurnon Focrors in Cotnpul-&?.S.vsrems, Toronto, Canada, April 1987.

N.L. Garrett, K.E. Smith, and N. Mcy-rowitz. “Intermedia: Issues, Strategies, andTactics in the Design of a HypermediaDocument System,” in Proc. Con/. onCompufer-Supporfed Cooperafive Work,MCC Software Technology Program, Aus-tin, Texas, 1986.

16.

Jsanircn,IamIfIS.

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16.

19.

N. Yankelovich, N. Meyrowitz, and A. vanDam, “Reading and Writing the Elcc-tronic Book,” Computer, October 1985.

N. Delislc and M. Schwartz, “Neptune: AHypertext System for CAD Applications.”Proc. o_f ACM SIGMOD Inr’l Con/. onManagement of Dafa, Washington, D.C.,May2830, 1986, pp. 132-143. (Alsoavail-able as SIGhlOD Record Vol. IS, No. 2,June 1986).

T ‘ . . -

nC-

n’s

A. diScssa. “A Principled Design for anIntcgrntcd Compufational Environment,”Humon-Computer Inferoaion, V o l . 1,Lawrence Erlbaum. 1985, pp. l-47.

K.M.Pitman. “CREF: An Editing Facilityfor Xtanaging S t r u c t u r e d Text,” A.I.Memo No. 829, M.J.T. A.1. Laboratory,Cambridge, .Mass.. February 1985.

ER September 1987

_, :_-.

20. P.J. Brown, “interactive Docutncma~ion.”in Softwore: Practice ond Exper i -ence. March 1986. pp. 291-299.

21. D. Shasha. “When Does Non-Linear TextHelp? fiperr Dotobase Systems, Proc. 01the First Inf’l Con/.. April 1986. pp.109-121.

22. A. Kay and A. Goldberg, “PersonalDynamic Media,” Compurer. March 1977,pp. 31-41.

23. T.W’. M a l o n e CI al. “JntelligentInformation-Sharing Systems,” Communi-colionr o/ fhe ACM, M a y 1987. pp.39042.

24. W.Cibson. Neuromoncer. Ace Science Fit-lion. 1984.

A more detailed version of this article,including an extended bibliography, is avail-able from the author. To obtain a copy, cir-cle number 181 on the Rcadcr Service Cardat the back of the magazine.

.’

E. Jeffrey Conklin is a m:mber of the rcscarc:staff and GE’s liaison to the Software Technology Program ht the Microzlectronicr and Cornpuler Technology Corporation (MCC). Hiresearch centers on constructing informatiorsyrtcms for the capture and USC of dcsigrrationale.

Conklin Received his BA from Ant&h Col-lege and his MS and PhD from the Universit)of Massachusetts at Amherst.

Readers may write to Conklin at MCCSofr-wareTechnology Program, P.O. Box 20019J.Austin, TX 78720; (512) 3.t3-0978.

User-Oriented Content-BasedText and Image Handling

MASSACHUSETTS INSTITUTE OF TECHKOLOGYCambridge, MA n March ZI- 24, 1988

General Theme: Information rctricval sysrcms for full-test a,ltl mixedmedia databases handling:

l techniques designed to reduceimprecision in full-text databasesearching

SpeciGc Themes:

m darn entry and control9 “friendly” cni-user inrcrf3ccs

9 new media

A) Linguistic processing and interrogation of full-text databases.B) Automatic thesaurus construction.C) Expert system techniques for rctricving information in full-tcxr and

multimedia databases.D) Friendly user interfaces to classical information retrieval svstcms.E) Specialized machines and system architecture designed fir treating full-

text data, including managing and accessing widely distributed databases.F) Automatic database construction using scanning techniques, optical

character readers, output document preparation, ctc . . .G) ScwapplicaZjons and pcrspcctivcs suggested by emerging new

technologies.

DEADLCI’ES:SEPTE.\IBER 30. 1987: Inrmtion ofsvbmi~?iqapnpcr.OCTOBER 30. 1487: Four copier sioufdbe r&&l/! rhc Conjrrrnrc Sn-rrrnn’nr.DECE.\IBER 16. 1987: Arcrpranrr nortjicarion.

Submit papers LO, or for more information:RIAO 88 Confcrcncc Scnicc Of&c. MIT. Bldg. 7. J1m. 111, Cambridge. \I.-\ 02 139 USA