Reprinted from Proceedings of the Conference
on
Computer-Supported Cooperative Work, Los Angeles,
CA, Oct 7-10, 1990, pp. 143-156. (AUGMENT,132082,).
Also republished in HypertextlHypermedia Handbook,
E. Berk & J. Devlin (Ed. ], McGraw-Hill, 1991.
KNOWLEDGE-DOMAIN
INTEROPERABILITY AND AN
OPEN HYPERDOCUMENT SYSTEM
Douglas C. Engelbart
Bootstrap Project, Stanford University
Sweet Hall, 3rd Floor
Stanford, California 94305-3090
Document #: (AUG 132082,)
INTRODUCTION
This paper anticipates that the tools and methods
of computer-supported cooperative work (CSCW) will become harnessed with
revolutionary benefit to the ongoing, everyday knowledge work within and
between larger organizations. Toward that end, the following concerns about
interoperability between knowledge-work domains will have to be met, and
something such as the "open hyperdocument system' must become available
for widespread use. 1 a
As computers become cheaper and we learn more about
harnessing them within our cooperative work, they will come to support an
increasing number of different domains of knowledge work. Moreover, the
sphere of computer-supported activities within each domain will steadily
expand as more function and more skill become employed. 1 b
It is predictable that increasing functional overlap
will occur as these expanding domains begin to overlap. It has become apparent
to me that someday all of our basic knowledge- work domains will be integrated
within one coherent 'organizational knowledge workshop. " This leads
to thinking about an over-all, integrated architectural approach to the
ever larger set of common knowledge work capabilities emerging within a
multi- vendor environment. 1 c
Much has been accomplished to date in standards
and protocols in the highly active field of networked workstations &
servers, where 'interoperability between hardware and/or software modules'
has become a central theme. 1 d
This paper considers the 'interoperability between
knowledge domains. ' This interoperability theme will be increasingly important
for a workable CSCW framework as the scope and degree of CSCW increases.
Dramatic increases will predictably create a marked paradigm shift about
how to organize and operate cooperative human endeavors. I think that two
phenomena will yield changes and a paradigm shift that will make this interoperability
of paramount importance: 1 e
(1) With a relatively unbounded technological frontier
together with immense and growing economic pressure, the speed, size and
cost of computers, memory, and digital communications will continue improving
by geometric progression;lel
(2) Awareness and importance of CSCW is emerging,
with a predictable trend toward our doing more and more of our personal
and cooperative knowledge-work online. 1e2
Assuming an inevitably gigantic scale for our inter-knit
'CSCW world" provides some important guidance for the continuing investment
of our business resources and professional time. 1f
For one thing, each year earlier that an effective
degree of knowledge-domain interoperability is in place within important
organizational or institutional domains could be worth hundreds of millions
of dollars -- could mean the difference between vitality and sluggishness.
1f1
And for another, we would prefer to avoid investing
our research, product development or organizational-change resources toward
ends that won't be interoperably compatible within that future, radically
different paradigm. I f2
INTEROPERABILITY IN AN INDIVIDUAL'S KNOWLEDGE
WORKSHOP2
To begin with some very basic knowledge-domain
interoperability issues, consider your own (future? ) 'Computer-Supported
Personal Work" (CSPW). Assume that you have acquired a fairly comprehensive,
online 'knowledge workshop," you have found better and better software
packages to support the kinds of as shown in Figure 1: 2a
Figure 1. Each functional domain is a candidate
for working interchange with all others.
2al
Consider what you will some day have when your
individual workshop inevitably becomes truly integrated. Between the E-Mail
and the task management files, or the status reports, or whatever, you really
would like to tie these functional domains together with a flexible free-flow
of information and linkages. 2b
What kind of interoperability do you have now?
I happen to think that the interoperability provided today within most CSPW
domains has a great deal of improvement yet to be pursued. But rd resist
any serious arguments about this unless it be approached within the context
of a coherent 'CSCW interoperability framework such as outlined below. Let
me say in warning, though, that from such a framework I will contend that
the marketplace for CSPW will change drastically as CSCW takes hold within
our larger organizations and their inter-organizational communities. 2c
INTEROPERABILITY IN A GROUP'S KNOWLEDGE WORKSHOP 3
Suppose that you and a colleague each have a fully
integrated CSPW domain, c(comprised of nicely interoperable sub-domains
as in Figure 1. And suppose that you want to work together online. consider
the interoperability between your respective knowledge-work domains, as
in Figure 2. 3a
Figure 2. Close cooperation between compound
knowledge domains puts new demands on knowledge-work interchange. 3a1
Now you're faced with a new challenge and a new
problem. You might set it up so you have a few lines d= cross between
domains, but why stop there? When do two people in intense cooperative work
NOT need total interoperability? In fact they depend on it heavily in the
paper world. Why not online? 3b
INTEROPERABILITY ACROSS TIME AND SPACE 4
Yet another example of multiple domains is found
in the familiar time-place matrix -shown in Figure 3. In many cases, activities
in the different quadrants involve the same substantive work content.
Is knowledge-work interoperability between the quadrant domains an issue?
Very much so. For example, face-to-face meetings need to flexibly utilize
anything from the whole organizational knowledge base, and the meeting's
records should immediately become an integral part of that same base
for later-time work. 4a
Figure 3. Collaborative processes generally
considered 4al
A Point About Online
Group Knowledge Work 5
The matrix in Figure 3 is very neat and
ordered. Here in Figure 4 I offer another picture of multi-domain, group
knowledge work which isn't so cleanly laid-out. This reflects how I feel
about the various knowledge-work domains with which my CSPW domain must
interoperate.
. 5al
The purpose of interoperability is to avoid having
information islands between which information cannot flow effectively. Since
we grew up in a paper-based framework, we've given little thought
about how much exchange and interoperability support we really do have,
and how much we depend upon it to be interoperable in our CSPW world we
could simply print out and hand over the hard copy. With WYSIWG screens
and Desktop Publishing, we're doing that with nicer paper, faster. 5b
So when we inevitably move from computer-supported
paper generation and exchange to computer-supported online creation and
exchange, we will need the same level of interoperability. And as the number
and scale of knowledge domains involved in a given CSCW "web"
increases, so does the need for "online interoperability. "5c
INTEROPERABILITY ACROSS KNOWLEDGE DOMAINS 6
To appreciate the extraordinary complexity of heavy
industrial knowledge work, and the associated requirements for interoperability,
consider the important functional domains within a large manufacturing organization
producing a complex product, such as an airplane. It is a serious enough
challenge to provide effective interoperability among the knowledge workers
within any one of the domains in Figure 5; just consider the inter-domain
challenge. And then consider that some of these domains, such as customers
and suppliers, exist 'outside' the organization, each with its own equally
complex multi-domain structure. 6a
Figure 5. Each functional domain is a candidate
for working interchange with all others.
THE LARGE MATRIX ORGANIZATION 7
An interesting example comes from my time at McDonnell
Douglas Corporation, where I marveled at how something as complex as one
of their airplanes gets a business plan, and gets designed, manufactured,
flown, and supported. Look at any given project or program (PI" through
'Pn" in Figure 6) , and the functional support thats required ('Fl"
through 'Fn') , and the exchange that needs to happen within that matrix.
7a
Figure 6. Consider the domains within a matrix
organization of projects and function.
7al
Each function has to share and exchange working
information with many programs, and each program
has to share and exchange with many functional support areas. Wherever
there isn't mutual interoperability, the workers at
the domain intersections will have to suffer
with inter-domain switching and converting - which is very expensive. Depending
upon this kind of functional program matrix environment
will require knowledge-domain interoperability
across the whole organization. 7b
THE AEROSPACE INDUSTRY AS A CASE IN POINT8
To really appreciate the magnitude of this situation,
let's look inside one of those aerospace programs. 8a
A Large Aerospace Program. McDonnell Aircraft Company
is participating in a bid to build the Advanced Tactical Fighter ("ATF)
for the Air Force. It's possibly one of the most technically complex products
anyone has ever dealt with. 8b
On top of that, they have an urgent mandate to
start practicing "concurrent engineering,' where the designers have
to work concurrently with the manufacturing engineers. This will require
intense back-and-forth cooperation between the two knowledge domains, which
no one really knows yet how to do on such a large scale. 8c
Also, significant design and manufacturing problems
are often delegated to the first-tier suppliers shown in Figure 7, so the
cooperation with that tier is also close and intense. Then the first tiers
hand off to the second tiers, and so on. So, all-in-all, you have something
like 6,000 companies cooperating -- each a separate, complex, knowledge-work
domain. They are expected to keep track of all business- and technical-exchange
records throughout the design and manufacturing process: 8d
Figure 7. Islands in supplier hierarchy of a
major aircraft program would be very costly.
8dl
I should point out here that the arrows in the
diagram represent the legal flow of contracts being awarded. The actual
exchange of documents would be shown as a two-way flow of continual negotiation
and refinement throughout the design and manufacturing process -- developing
the specifications, proposals, change orders, testing records, and so on.
And for any part within any airplane, the manufacturer must later be able
to identify when it was delivered, by whom, and even who was the shop foreman
at the time of assembly. 8e
Also, a program of this size in the aerospace world
would typically comprise a 10 to 30 year life cycle. So when we talk of
Different Time / Same Place, and Different Time /Different Place (Figure
3) , the definition of "Time' includes decades, not just hours or days.
Even in a short time span and without turnover, it is not unheard of for
a project team, in any industry, to occasionally lose sight of some important
design decision trails, and consequently waste time and money repeating
old discussions or past mistakes. Consider the likelihood, and the cost,
of such lost history occurring in this long-term environment. 8f
To comply with the Department of Defense's (DoD's)
forthcoming Computer-aided Acquisition and Logistic Support (CALS) mandate,
all documents exchanged between the DoD and its contractors must be transmits
updated, and managed in a standard, computerized form - a truly gigantic
interoperability challenge. 8g
Two Companies Teaming. The
situation is even more complex: as with most new, large-system, DoD procurements,
the Air Force requires ATF bidders to be joint-venture teams comprised of
major aerospace firms. In this case, McDonnell Aircraft is teaming with
Northrop Aircraft Figure 8 shows how Northrop would form its part of the
program, with several thousand workers internally, in close collaboration
with several tiers of suppliers: 8h
Figure 8. Islands in supplier hierarchy of a
major aircraft program would be very costly.
8hl
And then picture the two companies as a team (Figure
9) , and consider the intense demands for interoperable recorded document
exchange across functional support and project domains within this ATF-contractor
team -- within each company, between the two companies, and between them
and the DoD (remembering the CALS initiative). 8i
Figure 9. Close cooperation between large organizations
puts now demands on knowledge-work interchange.
8il
And then consider Figure 10 and all of the recorded
interchange between these two companies and their supplier hierarchies,
throughout the multi-decade fife cycle of the program. 8j
Figure 10. Teamed aerospace program -- immense
demand for knowledge-work exchange. 8jl
The Web Of
Aerospace Relationships. Now consider all the other large-program
webs of aerospace contractors, suppliers, and customers represented by the
small sub-set shown in Figure 11. A great many of these suppliers and customers
will work with many of the same contractors. The complexity becomes staggering.
Within such an inter-knit web of cooperative knowledge domains, there is
no practical solution for effective interoperability other than industry-wide
standards - adhered to by contractors, customers, and suppliers.
8k
Figure 11. With common customers and suppliers,
an aerospace industry can't afford islands.
8kl
And every other large industrial sector must also
achieve CSCW interoperability. And those sectors must themselves interact
effectively. The CSCW-interoperable web will cover the world, as has clearly
been or will be done for transportation and communica- tions (e. g. telegraph,
telephone, radio, or TV). I think a strong case can be made that
the cost of NOT having total knowledge-domain interoperability would
far exceed the cost of achieving this interoperability. 81
So how will this urgent need be satisfied -- for
intense, computer-supported cooperation across the knowledge domains
of our rapidly approaching future world? It would seem that our "CSCW
future" must include something like the solution characterized below
as "an open hyperdocument system. " And if so, then all of our
research, product development and application exploration should align with
and properly affect the concepts and principles by which the future state
is pursued. 8rn
Towards An Open Hyperdocument System9
Several years ago at McDonnell Douglas Corporation
we coined the term 'Open Hyperdocument System" (OHS) and began to define
the associated functional and interoperability requirements for the kind
of wide-area online cooperative knowledge work described above. This followed
several years of careful study, and some pilot trials--one of which involved
thousands of knowledge-workers using a prototype system containing many
of the required capabilities. 9a
Note: McDonnell Douglas is poised to move forward
with requirements such as below as the basis for functional specifications
and a workable procurement process. 9al
In the following, I assume a need to provide basic
capabilities so generic as to satisfy both the CSPW and CSCW application
requirements over a broad spectrum of knowledge domains within a wide variety
of organizations -- including for instance universities, standards groups,
and the U. S. Congress. 9b
SOME GENERAL ASSUMPTIONS 10
In an open hyperdocument system, basic standards for document architecture are of course
important But beyond that, facilities for creating,
transporting, storing, accessing and manipulating the hyperdocuments are
embedded within an open, interoperable information-system environment, and
the combined functionality is available within the knowledge-work domains
of every class of worker (working from any vendor's terminal/workstation
of suitable capability). Under these conditions, the role and value of hyperdocuments
within groups, and between groups, offers very significant improvements
in productive knowledge work. 10a
Two unique issues differentiate this new environment
from document-support systems to date: (1) interlinkage between objects
arbitrarily located within a large, multi-topic and extended-history document
& data collection; and (2) extensive, concurrent, online utilization
for creating, studying, organizing and linking within and between the many
overlapping and nested knowledge domains. 10b
These differences introduce paradigm shifts that
produce different system requirements from those that have been evolving
in the predominantly CSPW marketplace. For instance, WYSNWG will give way
to NWSIWYN -- "what you see is what you need (at the moment) "
-- providing different options for how you'd view selected portions of the
document space in your windows. The VRYSAWG view would be but one option
(and likely to be utilized with decreasing frequency). Other expected shifts
are implicit in some of the following suggested OHS requirements. 10c
Besides special, "document-system architecture"
features, full achievement of large-domain CSCW gains awaits two things:
10d
(1) widespread implementation of integrated, open-system
architectures; and10d1
(2) widespread adoption of new knowledge-work processes
(or, "knowledge processes"). 10d2
To me, these new knowledge processes are especially
relevant They will involve new systems of skills, conventions, roles, procedures,
methods and even organizational structures. I believe that they will provide
a much more effective matching of basic human capabilities to the heavy
knowledge-work and collaborative tasks within the functional human groupings
that we call "Organizations,' and within the mission-specific groupings
that we call 'projects.,,10e
In my experience, truly effective new knowledge
processes will emerge only via a co- evolutionary process -- new knowledge
processes and the new tools evolving together in real working environments.
Explicit evolutionary pursuit with numerous, well-run pilot groups, seems
called for. 10e1
From this is derived the position that a really
good set of requirements and functional specifications for an OHS can only
emerge from solid prototypical experience, in which advanced knowledge processes
were developed and exercised along with advanced tools. 10e2
Note that the following list was derived from extensive
experience with the evolution of the AUGMENT System (an OHS prototype owned
by McDonnell Douglas) and its concurrent application within numerous
real-work- pilots. 10e3
ESSENTIAL ELEMENTS OF AN OHS 11
Mixed Object Documents -- to
provide for an arbitrary mix of text, diagrams, equa- tions, tables, raster-scan
images (single fi-ames, or even live video) , spread sheets, recorded sound,
etc -- all bundled within a common "envelope" to be stored,
transmitted, read (played) and printed as a coherent entity called a
"document"11a
Explicitly Structured Documents -- where the objects comprising a document are arranged in
an explicit hierarchical structure, and compound-object substructures may
be explicitly addressed for access or manipulation of the structural relationships.
llb
View Control of
Objects' Form, Sequence, and Content -- where a structured,
mixed-object document may be displayed in a window according to a flexible
choice of viewing options -- especially by selective level clipping (outline
for viewing) , but also by filtering on content by truncation or some algorithmic
view that provides a more useful view of structure and/or object content
(including new sequences or groupings of objects that actually reside in
other documents). Editing on structure or object content from such special
views would be allowed whenever appropriate. llc
The Basic "Hyperdocument" -- where embedded objects called 'links" can point to
any arbitrary object within the document, or within another document in
a specified domain of documents - and the link can be actuated by
a user or an automatic process to "go see what is at the other end,'
or "bring the other-end object to this location,' or "execute
the process identified at the other end. " (These executable
processes may control peripheral devices such as CD ROM, video-disk players,
etc. ) lld
Hyperdocument "Back-Link" Capability
-- when reading a hyperdocument online,
a worker can utilize information about links from other objects within this
or other hyperdocuments that point to this hyperdocument -- or to designated
objects or passages of interest in this hyperdocument. 11e
The Hyperdocument "Library System"
-- where hyperdocuments can be submitted
to library-like service that catalogs them and guarantees access when referenced
by its catalog number, or "jumped to" with an appropriate link.
Links within newly submitted hyperdocuments can cite any passages within
any of the prior documents, and the backlink service lets the online reader
of a document detect and "go examine" any passage of a subsequent
document that has a link citing that passage. 11f
Hyperdocument Mail --
where an integrated, general-purpose mail service enables a hyperdocument
of any size to be mailed. Any embedded links are also faithfully transmitted
-- and any recipient can then follow those links to their designated targets
in other mail items, in common-access files, or in 'library" items.
llg
Personal Signature Encryption -- where a user can affix his personal signature to
a document, or a specified segment within the document, using a
private signature key. Users can verify that the signature is authentic
and that no bit of the signed document or document segment has been altered
since it was signed. llh
Access Control --
Hyperdocuments in personal, group, and library files can have access restrictions
down to the object level. Ili
Link Addresses That Are Readable and Interpretable
by Humans - one of the 'viewing options'
for displaying/printing a link object should provide a human-readable
description of the "address path" leading to the cited object;
AND, that the human must be able to read the path description, interpret
it, and follow it (find the destination "by hand" so to speak).
11j
Every Object Addressable
-- in principle, every object that someone might validly want/need to cite
should have an unambiguous address (capable of being portrayed in a manner
as to be human readable and interpretable). (e. g., not acceptable to be
unable to link to an object within a 'frame' or 'card. ') llk
Hard-Copy Print Options to Show Addresses of Objects and Address
Specification of Links -- so that, besides
online workers being able to follow a link-citation path (manually, or via
an automatic link jump) , people working with associated hard copy can read
and interpret the link-citation, and follow the indicated path to the cited
object in the designated hard-copy document. 11l
Also, suppose that a hard-copy worker wants to
have a link to a given object established in the online file. By
visual inspection of the hard copy, he should be able to determine a valid
address 'path to that object and for instance hand-write an appropriate
link specification for later online entry, or dictate it over a phone to
a colleague. 11l1
HYPERDOCUMENTS IN A GENERAL INTEGRATED
ARCHITECTURE 12
Besides the aforementioned Hyperdocument Mail and
Hyperdocument Library features, there are other important CSCW features
that are dependent upon an 'integrated system". 12a
Shared-Window Teleconferencing -- where remote distributed workers can each execute a
related support service that provides the "viewing" workers
with a complete dynamic image of the "showing" worker's window(s).
Used in conjunction with a phone call (or conference call) , the parties
can work as if they are sitting side-by-side, to review, draft, or modify
a document, provide coaching or consulting, and so on. Control of the application
program (residing in the 'showing' worker's environment) can be passed around
freely among the participants. 12b
Inter-Linkage Between Hyperdocuments and Other
Data Systems - for instance, a CAD system's
data base can have links from annotations/comments associated with a design
object that point to relevant specifications, requirements, arguments, etc.
of relevance in a hyperdocument data base -- and the back-link service would
show hyperdocument readers which passages were cited from the CAD data base
(or specified parts thereof). 12c
Similarly, links in the hyperdocuments may point
to objects within the CAD bases. And, during later study of some object
within the CAD model, the back-link service could inform the CAD worker
as to which hyperdocument passages cited that object. 12cl
External-Document Control
(XDOC) -- Same 'catalog system' as for hyperdocument libraries --
with back-link service to indicate links from hyperdocument (and
other) data bases, for any relevant material that resides offline or otherwise
external to the OHS. 12d
THE INTEROPERABLE OHS ENVIRONMENT13
Here's what the share-and-exchange domain within
an open hyperdocument system might look like: 13a
Figure 12. Knowledge-domain interoperability
is greatly enhanced by hypertext linkage capability.
13al
The requirements outlined above form a basic
support platform for any group knowledge work effort, with interoperability
across time and space (including all quadrants of the Time / Place matrix)
, across knowledge domains, and across organizational domains. 13b
THE INTEROPERABILITY INVESTMENT 14
It could take a lot of effort and expense to get
such knowledge-work interoperability. You might say, "Why don't I just
do the part that's important? ", as in Figure 13, Choice A. Someone
else's idea of what's important to share and exchange may look like Choice
B: 14a
Figure 13. Providing for extensive interoperability
will be expensive. 14al
As more and more of the knowledge work in each
domain is done online, then the benefits of a comprehensive degree of CSCW
interoperability will rapidly increase. 14b
How do you decide how far to go? You'd compare
the value of A vs. B, or B vs. C. And you'd say, "Well, lets see, with
each successive choice I'd save more money, wouldn't I? " So how much
more? We don't know how to quantify it yet. But, once you start finding
a way to make some of the major sub-domains interoperable, by the time you've
picked these selective lines in Choice A or B, what would be the incremental
cost in dollars and effort to get Choice C? 14c
But the -real question is, what does it cost in
dollars and effort NOT to have the interoperability. 14d
THE OHS MOVEMENT 15
I asked people familiar with complex aerospace
projects, "Well all right, let's make a guess -- if the kind of hyperdocument
interoperability we are talking about here were installed for instance under
the whole design & manufacturing operation of this ATF program, what
might the yearly dollar benefit be? " They look back and forth at each
other for a while . . . So I offer "$300,000,000 a year? "
And they look at it and say, "At least. "15a
User organizations must realize that they can't
just sit back and wait for the standards groups and computer vendors to
deliver this, because there hasn't yet been enough orientation or application
experience in this area. It seems necessary for the larger user organizations
to take responsibility, to become pro-active -- e. g., with exploratory
pilots, active development of associated knowledge processes, and cooperative
requirements definition -- and then show the vendors that there is a sizable
market for this. 15b
But they must also realize that it isn't just a
matter of specifying, procuring, and installing the resulting system --
they have to learn how to employ it effectively in this extremely complex
environment And they must realize that they have to cooperate more intensively
than before: The stakes are extremely large; there is too much to learn
and events are moving too rapidly; the resources and degree of stakeholder
coordination involved are both very high. 15c
To find this effort emerging from within the aerospace
industry seems likely enough to me: it is the most complex work environment
I know of, and a most urgent candidate for harnessing the benefits
of wide-area CSCW and effective knowledge-domain interoperability. But other
large organizations also have pressing needs for exactly this same capability
-- for example, car manufacturers, computer vendors, government agencies,
consulting firms, universities, consortia, and standards groups. 15d
To me there is a real need for a cooperative movement
-- among large organizations that are heavily dependent on group knowledge
work - to coordinate planning and operation of advanced, cost-effective
pilot explorations in this area and to share the experiences and results.
This relates to what I am currently doing at Stanford University with the
Bootstrap Project: exploring with a number of larger organizations how a
"cooperative, CSCW community' could be set up and run to provide both
valuable pilot-application experience and substantive knowledge products.
One of the first projects of this community would
be to collaborate on the requirements for an open hyperdocument system,
and on a procurement approach. The community would employ a prototype OHS
platform (initially AUGMENT from McDonnell Douglas) to collaborate on this
and other related projects. This hands-on experience will be an important
part of the exercise, and should provide valuable insight into how to employ
these capabilities effectively. Similar pilot trials will be launched within
member organizations. 15f
ACKNOWLEDGEMENTS: 1 6
This work was sponsored by grants from the Kapor
Family Foundation, Sun Micro-systems, Inc., and Apple Computer, Inc. 16a
For more background on the source experience from
which these proposed OHS require-ments grew: 1 7
Engelbart, Douglas C., "Toward High-Performance
Knowledge Workers," OAC '82 Digest, Procedings of the AFIPS Office
Automation Conference, San Francisco, April 5- 7, 1982, p. 279-290 (AUGMENT,81010,).
Re-published in "Computer Supported Cooperative Work: A Book
of Readings," ed. Irene Greif, Morgan Kaufmann Publishers, Inc., San
Mateo, CA, 1988, pp 67-78. 17a
Engelbart, Douglas C., "Authorship Provisions
in AUGMENT," COMPCON '84 Digest, Procedings of the 1984 COMPCON
Conference, San Francisco, CA, Feb 27-Mar 1, pp. 465-472 (OAD,2250,).
Re-published in "Computer Supported Cooperative Work: A Book of Readings,"
ed. Irene Greif, Morgan Kaufmann Publishers, Inc., San Mateo, CA, 1988,
pp 67-78. 17b
Engelbart, Douglas C., and Lehtiman, Harvey G., "Working Together," BYTE magazine, December 1988, pp. 245-252. 17c [an error occurred while processing this directive]