 
           

 THE XANADU HYPERTEXT SYSTEM: 

A NEW DOCUMENTATION MANAGEMENT TOOL 

INTRODUCTION 
  

A new documentation management tool, 
"hypertext", lets the user, rather 
than the software system, decide how 
information will be interrelated and 
stored. It is a system designed to 
handle text in all of it's 
complexity. Today's technical 
communicator faces information 
management nightmares such as 
changing one basic manual to reflect 
the differences in several 
installations, or to suit each 
particular customer's needs. 
Hypertext offers a unified way to 
solve such problems. 

Currently, most documentation 
management consists of two phases.  
First, a document is written or 
edited using a text editor or word 
processing software package.  It is 
then kept track of using storage and 
retrieval systems such as database 
management systems, keyword systems, 
or fulltext search systems. These 
systems  implicitly determine the 
interconnections and comparisons a 
user can make between documents, 
whereas hypertext systems allow the 
user to make explicit 
interconnections called "links".  To 
understand why hypertext systems are 
a unique concept, let us look more 
closely at word processing and some 
of the more popular storage and 
retrieval methods.  
  A LOOK AT CURRENT DOCUMENTATION 
MANAGEMENT SYSTEMS 
  Word processors and text editors 
are fine tools for manipulating text 
within documents, but are usually not 
well coordinated with storage and 
retrieval functions.  They generally 
do not deal with relationships 
between documents that may exist.  As 
Ted Nelson says (1), this state of 
affairs forces the writer or editor 
to stop working at the boundaries of 
a document, which, to some extent, 
limits thought.  There is no 
convenient way to show relations 
between documents. Also, word 
processors and text editors often 
tend to limit the size of the 
documents a user can work with.  
Storing documents in files means that 
the user has to think up file names, 
worry about file conventions, and 
keep track of files on paper, or with 
a separate system.  Most text editors 
or word processors have no way to 
keep track of changes resulting from 
the editing process other than 
keeping an old copy and a new copy 
online or a trail of all the editing 
changes.  This means storing a lot of 
copies.  
  In keyword  systems, keywords are 
usually attached to a text for 
reference. A user asks the system to 
find all the articles with certain 
keywords contained within them, and 
it searches thru its database looking 
for them. Keyword systems function 
well as card catalogs; however, since 
not all thoughts can be expressed in 
one word, problems arise.  What seems 
an obvious keyword to you may not be 
a keyword to the author.  Thus the 
article is not listed by the word 
that you may be looking for, though 
it may be listed by keywords that you 
have not thought of.  Keyword systems 
are not designed to let a user edit 
while remaining within the system.  
Explicit citations within or between 
documents cannot be created. 

Keyword systems are a subset of the 
more general type of storage and 
retreival system called fulltext 
search systems.  With fulltext search 
systems, a user types  something like 
a phrase or a sentence which might be 
found in the document he or she 
wishes to find.  The system searches 
its database for the text until the 
desired document is located.  
Fulltext search systems give users 
more latitude in expressing thought 
than keyword systems, thereby 
increasing the user's chances of 
finding all the pertinent references. 
But like keyword systems, fulltext 
search systems do not let users edit 
without exiting from the system.  
They do not allow users to make 
explicit citations, notes, or other 
connections between documents.  

Data base management systems, or 
DBMS, provide excellent means of 
storing and retrieving any type of 
data which will fit into a fixed 
field format.  Any data that can be 
grouped into lists may be stored in a 
database management system, which 
will let users make certain kinds of 
very useful comparisons between the 
fixed fields.  Parts lists, numerical 
data, and personnel records are 
examples of data best suited to these 
systems.  Data base management 
systems are not optimized to edit, 
store, or retrieve documents because 
text is too complicated.  DBMS are 
sometimes used for keeping track of 
names of journals or articles.  
Because there is often no standard 
way of abbreviating journal names, 
users may have problems with this 
application.  

The following table, Table 1, 
summarizes the differences between 
current documentation management 
tools and the Xanadu Hypertext 
System. 
  HYPERTEXT: NONSEQUENTIAL WRITING 

As the above discussion shows, the 
current approach to documentation 
management  requires more than one 
tool to work with text and is 
restrictive when users need to 
interrelate documents.  However, the 
real problem is that current systems 
are not designed to let people use 
computers in the same way and with 
the same ease that they use paper.  
Hypertext, which means nonsequential 
writing, is a system based on the way 
we use paper to read, write and file. 
The term was coined by Nelson, the 
originator of the concept (2,3). 

To understand what nonsequential 
writing means, let us look at an 
example that will be familiar to many 
technical communicators.  Consider 
the amount and the complexity of 
paperwork required to build an 
airplane.  

Suppose that the project engineer 
decides to move the wings on an 
airplane to a slightly different 
position on the fuselage.  Many 
design documents will be affected by 
this change, perhaps thousands of 
them.  To change the wing, he must 
first find all the components that 
will need to be modified.  The change 
must then be made, but only after 
searching through the blueprints to 
make sure that this change will not 
adversely affect anything else.  Once 
this is done, the technical 
communicators must update all 
affected documents to reflect the 
changes. 

For something as seemingly trivial as 
changing the position of one bolt, 
the engineer has to know what 
components may be affected.  For 
example, rewiring may be required if 
the bolt is moved into the path of a 
cable.  Since our fictitious 
aerospace company doesn't have 
strings connecting its technical 
documents together,  the writer or 
someone in the project must spend an 
appreciable amount of time chasing 
down all the documents which refer to 
that bolt.  A common expression in 
the aerospace industry is, "When the 
paperwork weighs as much as the 
aircraft, the plane is finished."  

In the above example all documents 
(including blueprints) written about 
that plane constitute a literature, 
or a hypertext. Because everything 
contained within this literature 
concerns some aspect of the airplane, 
it is interconnected, as if by a 
network of invisible strings. 
  DEVELOPMENT OF HYPERTEXT 

The idea of hypertext was born in 
1960 when Ted Nelson decided to 
design a computer system which would 
allow him to make multiple versions 
of articles or documents out of the 
same pieces of text.  His ideas on 
hypertext and on what computers could 
be like were published in the 1974 
underground classic 

Computer Lib/Dream Machines. 

The book attracted the attention of 
some brilliant young men who joined 
Nelson.  They finished designing and 
began implementing a hypertext system 
that could retrieve hypertext in a 
reasonable response time out of a 
database (or "docuverse") as large as 
a world library (4). 
 The effort, named Project Xanadu, 
created the Xanadu(tm) Hypertext 
System.  It licensed a company, XOC, 
to market the system for commercial 
applications. 

Douglas Engelbart and Andries van Dam 
have also done major work in the 
field of hypertext.  Douglas 
Engelbart began work on an interactve 
editor and form of hypertext called 
NLS in 1959 (5). 
 He is considered to be the father of 
several concepts related to hypertext 
such as word processing, networking, 
and teleconferencing. Now at 
TymeShare, his system is currently in 
use over a worlwide network..  The 
system is now called "Augment".  It 
differs from Xanadu Hypertext in 
several aspects, the most notable 
being that links are embedded in the 
text and it is only capable of 
functioning with limited databases.  

Andries van Dam implemented the first 
hypertext system in conjunction with 
Nelson at Brown University in 1968 
(6). Since then two other hypertext 
systems have been implemented at 
Brown (7).  Other hypertext research 
involved a prolonged use of hypertext 
in a poetry class (8).  

I will be discussing hypertext as it 
is being implemented by XOC for the 
rest of this paper both because I am 
most familiar with it and because it 
is the most ambitious hypertext 
project to date.  For a more complete 
discussion of other forms of 
hypertext mentioned see the excellent 
review article on interactive editing 
systems by Meyrowitz and van Dam (9). 

THE XANADU HYPERTEXT SYSTEM  

My colleagues at XOC who designed the 
Xanadu Hypertext System wanted it to 
be so simple that a child (or an 
English major!) could use it. 
Therefore they createda system design 
that lets us hide all the arcane and 
proprietary inner workings from 
users.  Our system has two parts- a 
"backend" that the user never sees, 
and a "frontend" that the user sees 
and uses. Don't be misled, however; 
this does not mean that the user sees 
two parts.  It simply refers to 
internal organization of functions 
within a unified system.  

The backend is responsible for 
storage and retrieval functions. This 
part of the system runs on large or 
very powerful computers which can be 
networked together. Every Xanadu 
Hypertext System will have the same 
type of backend.  

The frontend is responsible for 
display function and user 
interaction, including editing.  
Frontend software will be modified to 
fit onto various types and sizes of 
computers, including personal 
computers.  Since users and their 
needs differ, our designers wanted to 
make sure that the part of the system 
that they use may be modified to fit 
their tastes and preferences.  

The Xanadu system is built out of 
"documents" and "links".  A document 
is defined to be a string of 
contiguous characters.  Thus a 
document may be text, graphics, 
blueprints, numbers, data, digitized 
voice, or music.  Text that a user 
may want to store and link on a 
Xanadu could be in the form of memos, 
technical documentation, business 
letters, marginal notes, citations, 
grafitti, or hypertext poetry.  The 
contents of documents and the 
connections between them are limited 
only be a user's creativity.  
  These explicit connections within a 
document or between documents are 
called "links".  Arbitrary pieces of 
arbitrary documents and links 
themselves may be linked together.  
Links can be retrieved at will, along 
with information about what is being 
linked to what and about the nature 
and type of the link itself. A link 
is bidirectional so you can tell 
which point it came from and where it 
is going.  The system can correctly 
maintain these links in the midst of 
changes to the very data being 
interlinked.  
  There are different link types for 
different purposes.  Although just 
how a link type is displayed depends 
on which frontend is used, the 
general forms can be discussed.  
Jumplinks are used to follow 
citations.  In the current 
experimental frontend, a user sees 
jumplinks as reverse video areas in 
the text he or she is reading.  To 
find the other end of a jumplink or 
any other link type, the user merely 
hits a control key on the computer 
keyboard.  A window large enough to 
display the cited text opens within 
the original document so that the 
user may read the pertinent material, 
then continue reading the original 
text.  If the new material proves to 
be more interesting, the user can 
enlarge the window and read the new 
document rather than the original.  

Say that a user begins reading a 
document, and that he or she sees an 
interesting looking jump link to 
follow.  After following the jump 
link, the user sees a second 
interesting citation within the 
windowed document.  The user may 
"pass through the window" and call up 
a third document.  If the third 
document proves to be uninteresting, 
the user may follow the same links 
back to his or her original document. 
Xanadu links allow users to pass 
through an infinite number of windows 
and back again (only a certain number 
of windows will be displayed on the 
screen at once).  Nelson refers to 
this action as "navigating through 
the docuverse" (10). 

Other link types include quote links, 
footnote links, and marginnote links. 
They differ from jumplinks and each 
other only in the way in which they 
are indicated within a document, and 
where their type and size of display 
window will appear on the screen.  
  Perhaps the most useful feature of 
Xanadu for writers is its versioning 
capacity.  Xanadu hypertext can 
maintain multiple versions of any 
given document, efficiently storing 
the common portions in common, with 
separate portions of storage required 
only for those parts of the documents 
which are actually different.  

The frontend will display a 
vertically split screen with a 
different version of the document 
shown on either side.  
Correspondences between versions will 
be indicated with connecting lines, 
and users will be able to scroll 
around in either version and edit.  

All such editing wil be logged by 
Xanadu's historical trace function.  
Xanadu can provide historical 
traceback information in dated 
chronological order about any and all 
changes to a given document.  It can 
do all of this efficiently, with only 
logarithmic overhead in terms of both 
storage space and response time. For 
example, if the number of stored 
documents increases geometrically, 
the response time required to locate 
a particular one will increase only 
linearly. 

Historical trace is not yet 
implemented, but it might look 
something like a branching tree on a 
future frontend.  A user could scroll 
along the tree with a mouse or a 
cursor until he or she reached the 
branch indicating the desired version 
of the document.  A touch of a 
control key would display the 
document and associated traceback 
information on the screen.  
  USES OF HYPERTEXT 
  As the above discussion shows, the 
Xanadu hypertext system can help the 
technical communicator perform a 
variety of tasks with greater 
efficiency.  The linkage and 
versioning capacities will make  
documentation updates less of a 
chore.  Theversioning facility can 
greatly help those who need to edit 
previously written materials into new 
documentation.  Links make it 
possible for communicators to easily 
keep track of their own and their 
departments' work, and to obtain 
feedback from users of online 
documentation.  User feedback logs 
can be constructed by allowing users 
to link their own comments to text 
they find obscure or confusing. 
  A unified information management 
system would also be useful to 
personnel outside the technical 
communications department.  A 
hypertext system is such a general 
tool that it can be used for office 
automation, conferencing, and 
engineering projects. Hypertext is 
ideal for managers and executives who 
need a way to have iformation at 
their fingertips.  It would enable 
them to make better decisions without 
wasting valuable time in meetings and 
papershuffling. 
  As of this writing the Xanadu 
organization has a working hypertext 
demonstration and plans to deliver a 
working prototype system  within the 
year.  Different kinds of links work 
but the backend still requires six 
months to a year development work 
before the Xanadu Hypertext System is 
an "off the shelf product".  
Currently, the system runs on a 
Sun(trademark of Sun Microsystems) 
68000 Workstation.  It is written in 
the 'C' programming language running 
under the UNIX(trademark of Bell 
Laboratories) operating system, and 
can be made to work on almost any 
computer.  When completed it will run 
on larger,modern machines with 
frontends running on a variety of 
machines, depending on demand.  

SUMMARY 
  In summary, a new, more powerful 
and unified documentation management 
system called the Xanadu Hypertext 
System will soon be available.  It 
will give users the freedom to 
organize documents to fit their 
needs, rather than the computer's. 
  

References  

(1) Nelson, T.H., "Replacing the 
Printed Word", INFORMATION PROCESSING 
80, S.H. Lavington, (ed.), North 
Holland Publishing Company, IFIP, 
1980 pp. 1013-23 

(2) Nelson, T.H., 

Computer Lib/Dream Machines, 

The Distributors, South Bend, IN., 
1974 

(3),(4),(10) Nelson, T.H., 

Literary Machines, 

T.H. Nelson, Swarthmore, PA., 1981 

(5) Engelbart, D.C.,  "The augmented 
knowledge workship" in Proc. National 
Computer Conf., vol. 42, AFIPS Press, 
Arlington, VA., 1973, pp.9-21  

(6)Carmody, S., Gross, W., Nelson, 
T.H., Rice, D.E., and van Dam, A. "A  
hypertext editing concept for the 
/360," in Pertinent Concepts in 
Computer Graphics, M. Faiman and 
Nievergelt, J., Eds., University of 
Illinois Press, Urbana, Ill., 1969 
pp. 291-330 

(7),(9) Meyrowitz, N., and van Dam, 
A. "Interactive Editing Systems, 
parts I and II", Computing Surveys of 
the ACM 14 (1982),  321-353 

(8) Catano, J.  "Poetry and 
Computers:  Experimenting with the 
Communal Text," Comput. Hum. 13 
(1979), 269-275  
