SURVEY & TUTORIAL SERIES Hypertext: An Introduction and SurvevJ Jeff Conklin Microelectronics and Computer Technology Corp. ost modern computer sys- design issues that go into fashioning a tems share a foundation hypertext environment. which is built of directories containing files. The files consist of text which is composed of characters. The text Hypertext systems that is stored within this hierarchy is linear. feature machine- For much of our current way of doing graphically (as labelled tokens) and in the business, this linear organization is suffi- supported links-both database (as pointers). (See Figure I .) cicnt. Howcvcr, for morcand moreappli- within and between But this simple idea is creating much cations, a linear organization is not excitement. Several universities have adequate. For example, the documenta- documents-that open created laboratories for research on hyper- tion of a computer program* is usually text, many articles have been written about either squcczcd into the margins of the exciting new the concept just within the last year, and program, in which case it is generally too possibilities for u!Gng the Smithsonian Institute has created a terse to be useful, or it is interleaved with demonstration laboratory to develop and the text of the program, a practice which the computer as a display hypertext technologies. What is all breaks up the flow of both program and communication and the fuss about? Why are some people will- documentation. ing to make extravagant claims for hyper- As workstations grow cheaper, more thinking tool. text, calling it “idea processing” and “the powerful, and more available, new possi- basis for global scientific literature”? bilities emerge for extending the tradi- In this article I will attempt to gc~ at the tional notion of “flat” text files by essence of hypertext. I will discuss its allowing more complex organizations of advantages and disadvantages. I will show the material. Mechanisms are being that this-new technology- opens some very devised which allow direct machine- exciting possibilii;es, particularly for new supported references from one textual pioneers of hypertext, once defined it as ‘?i’ uses of the computer as a communication chunk to another; new interfaces provide Tcorn-.*‘b’ ma I$ onofnaturallanguageiejit’iiriih ‘-’ fand thinking tool. However, the reader the user with the ability to interact directly ‘_Ihe c&puter*s capacity for interacti&* _ who has not used hypertext should espcct with these chunks and IO establish new s branching, or dynamic display. of a that at best he will gain a pcrccption of relationships bctwcen them. Theseexten- iL non~neartext_ . ~whichcannot~p,+.,t~ hypertext as a collection of intcrcsting fca- sions of the’traditional text fall under ihe ”conveniently on a conventional page.“’ cures. Just as a description of electronic general category of hyperkxf (also known This article is a survey of existing hyper- spreadsheets will not get across the real elc- as noniineurfext). Ted Nelson, one of the text systems, their applications, and their gancc of that tool, this article can only hint design. It is both an introduction to the at the potentials of hypertext. In fact, one 'D~cumm~a~ion is Ihe uncrccutablc English text world of hypertext and, at a deeper cut, a must work in current hypertext environ- which explains the logic of the program which it accompanies. survey of some of the most important ments for a while for the collection of fea- September 1987 0018-9162/81/o9ooM)11501.00~~961 IEEE that is common’io many hypertext systems I is the heavy use of windows that have a : one-to-one correspondence with nodes in. ., the database. 1 consider this feature to be of secondary importance. A I One way to delimit hypertext is to point out what it is not. Briefly, several systems B have some of the attributes Sf hypertext CL3 but do not qualify. Window systems fall 4, into this category; while window systems do have some of the interface functional- ’ I I could claim that a file system is a database, I I I i I I : Display screen and that one movef amongnodes(files) by 8I ,8 : II ,1 : t1 8I ,I --AI -L-_I_------ r I It I 1 I : I :i , I I @~m~t;,3imilarly, most outline proces- I sor’s (such as ThinkTank) do not qualify. I They provide little or no support for refer- I ences between outline entries, although their integrated hierarchical database and I interface do approximate hypertext better I than the other systems that I have men- I tioned. Text formatting systems (such as I I Troff and Scribe) do not qua!ify. They allow a tree of text fragments in separate I I files to be gathered into one large docu- !-I I- ----_--------- -I ment; however, this structure is hierarchi- Hyperlext database cal and provides no interface for on-line navigation within the (essentially linear) document. Similarly, database manage- Figure 1. The correspondence bctwccn windows and links in the display, and nodes ment systems (DBMSs) have links of var- and links in the dafabasc. In this example, each node in the hypertext database is ious kinds (for example, relational and displayed in a separate window on the screen when requested. The link named “b” object-oriented links), but lack the single in window A has been activated by a pointing device, causing a new window named coherent interface to the database which “B” IO be created on the screen and filled wifh the text from node B in the data- is the hallmark o[ hypertext. _ base. (Gcncrall~. links can have names that arc different from the name of the fqS’~ideodisCie~~orb~~m~~g~.~ .., _I node they point to.) ,‘fhere is,&&in~~~~~~est in theext+& 6&3&i I. $+Xztext to the~n$+~en&l &cept or. ype&&in which_ th;&‘n;$ii wh’ich’~ ‘i“y’iI P are i n&&k$ _. tog&h&, can be- &t, F r &- -+raphiF, digitized speech, audio record- a ‘T; !’ ISI@, picty~e;s, animatir+ film clips, and ,.. .JE, ‘Sistimably,_ _.“..--ttast&‘pdors --.-a and tactilcsentz. F i tures to coalesce into a useful tool. At thu pomt, httle has been done i the design and engineering t One problem with identifying the i tial aspects of hypertext is that the term these additional modalities, “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 primarily systems, elccrronic mail, and telecon- *While this arliclc seeks to establish the criterion cl address the more conservative text-based i ferenckg share iearures with hypertext. mxhinc-supvrlcd links as the prims? crilcrion of systems. hypertext. this is by no means an xccp~rd definition. This anicle focuses on machine-supported Thcrcforc I will also rcvicw 3nd discuss 3cvnc syrwnr links (both within and between docu- wblch have a weaker notion 01 links. A glimpse of using hypcrtcxt. It is USC- I I8 COMPUTER ‘._ ~.‘. -. _- _, i i ( - ,_’ ._ _ A. “_ ,; . ._ - ~-. -. : r .-*. ful IO have a sense of the central aspects of using a hypertext system, particularly if you have never seen one. Below is a list of _ , * Display screen wilh Wwsrr the features of a somewhat idealized hypertext system. Some existing systems I pXnt have more features than these, and some /stems lertext ns fall ‘stems ional- :I” of single and each has a name or title which e lack ,is always d&played in the window. How- le sys- ever, only a small number of nodes are .t; one yver “open” (as windows) on the screen at Ibase, the same time. ‘cs) by l Standard window system operations their are supported: Windows can be reposi- rtext, tioned, resized, closed, and put aside as. icated small window icons. The position and size more of a window or icon (and perhaps also its Yerely color and shape) arecues to remembering :ditor the contents of the window. Closing a win- -oces- dow causes the window to disappear after alify. any changes that have been made aresaved refer- to the database node. Clicking with the ough mouse on the icon of a closed window e and causes the window to open instantly,. ,_ ,. _. )e i \ .* Windows can contain any number of: n Jink.ico,p+ thich repiesent-pointers to C. other nodes in the database. The link icon They contains a short textual field which sug- Irate gcsts the contents of the node it points to. locu- Clicking on a !ink icon with the mouse rchi- causes the system to find the referenced L -----__--____- 1 .-line node and to immediately open a new win- Hypertext database Icar) dow for it on the screen. ._ ._ : _ iage- ,, l The user can easily create new nodes i var- and new links to new nodes (for anhota- Figure 2. The screen at the top illustrates how a hypertext browser provides a direct and lion, comment; elaboration, etc.) or to two-dimensional graphic view of the underlying database. In this illustration, the ;nglc existing nodes (for establishing new con- node “A” has been selected for full display of its contents. Notice that in the hich nections). _,_.. browser view you can tell not only which nodes are linked IO A but also how the I l Thedatabasecaribebrdwsedin tliiii--“subnetwork fits into the larger hyperdocument. (Of course, hyperdocuments of an> age, ways: (1) by following links and opening ‘size cannot be shown all al once in a browser-only portions can be displayed.) an of windows successively to examine their Con-_:? ‘_.