Buxton, W. (1995). Ubiquitous Media and the Active Office . Published
in Japanese (only) as, Buxton, W. (1995). Ubiquitous Video, Nikkei Electronics,
3.27 (no. 632), 187-195.
Ubiquitous Media and the Active Office
Bill Buxton
University of Toronto & Xerox PARC[1]
UbiMedia = UbiComp + UbiVid
In 1991, Mark Weiser published an article that outlined Xerox PARC's vision
of the next generation of computation (Weiser, 1991). He referred to this
model as Ubiquitous Computing, or UbiComp. In what follows,
we introduce a complimentary component of Weiser's story: what we call Ubiquitous
Video, or UbiVid.
The groundwork for UbiVid was laid by research into in "media spaces"
(Gaver et al., 1992; Mantei et al., 1991; Stults, 1986; Bly,
Harrison & Irwin, 1993). The ideas that we discuss build upon this work.
We argue that UbiComp and UbiVid are two sides to the same story. Together,
they make up something that may best be called Ubiquitous Media, or
UbiMedia. Our belief is that this notion of Ubiquitous Media provides
a useful model for conceiving of future systems and their usage models.
This paper is based on research undertaken at Xerox PARC, Rank Xerox EuroPARC
and the Ontario Telepresence Project. Many of the ideas discussed have been
implemented or prototyped. Many more have not. Our purpose here, however,
is not to report on research per se. Rather, our intent is to convey
the model of future computation that lies behind much of our work. Our hope
is to aid communication and provide the basis for future discussion.
UbiComp: a Brief Review
As described by Weiser, UbiComp can be characterized by two main attributes:
* Ubiquity: Interactions are not channeled through a single workstation.
Access to computation is "everywhere." For example, in one's office
there would be 10's of computers, displays, etc. These would range from
watch sized Tabs, through notebook sized Pads, to whiteboard
sized Boards. All would be networked. Wireless networks would be
widely available to support mobile and remote access.
* Transparency: This technology is non intrusive and is as invisible
and as integrated into the general ecology of the home or work place as,
for example, a desk, chair, or book.
These two attributes present an apparent paradox: how can something be everywhere
yet be invisible? Resolving this paradox leads us to the essence of the
underlying idea. The point is not that one cannot see (hear or touch) the
technology; rather, that its presence does not intrude into the environment
of the workplace (either in terms of physical space or the activities being
performed). Like the conventional technology of the workplace (architecture
and furniture, for example), its use is clear, and its physical instantiation
is tailored specifically for the space and the function for which it is
intended. Central to UbiComp is a break from the "Henry Ford"
model of computation in which, can be paraphrased asfsim:
You can have it in any form you want as long as it has a mouse, keyboard
and display.
Fitting the square peg of the breadth of real needs and applications into
the round hole of conventional designs, such as the GUI, has no place in
the UbiComp model.
Technology Warms Up
We can most easily place Weiser's model in historical perspective by the
use of an analogy with heating systems. In earliest times, architecture
(at least in cold climates) was dominated by the need to contain heat. Special
structures were built to contain an open fire without burning down. Likewise,
in the early days, special structures were built to house computation. These
were known as "computer centres."
As architecture progressed, buildings were constructed where fires were
contained in fireplaces, thereby permitting heat in more than one room.
Nevertheless, only special rooms had fire since having a fireplace required
adjacency to a chimney. Similarly, the next generation of computation was
available in rooms outside of computer centres; however, these had to have
special electrical cabling and air conditioning. Therefore, computation
was still restricted to special "computer rooms."
In the next generation of heating system, we moved to Franklin stoves and
even to radiators. Now we could have heat in every room. This required the
"plumbing" to distribute the system, however. The intrusion of
this "plumbing" into the living space was viewed as a small price
to pay for distributed access to heat. Again, this is not unlike the next
generation of computation, (the generation in which we are now living),
where we have access to distributed computation everywhere, as long as we
are connected to the "plumbing" infrastructure. And like the heating
system, this implies both an intrusion into the space and an "anchor"
that limits mobility.
This leads us to the next (today's) generation of heating system: climate
control. Here, all aspects of the interior climate (heat, air conditioning,
humidity, etc.) is controllable on a room-by-room basis. What actually provides
this is invisible and is likely unknown (heat-pump, gas, oil, electricity?).
All that we have in the space is a control that lets one tailor the climate
to their individual preference. This is the heating equivalent of UbiComp:
the service is ubiquitous, yet the delivery is invisible. In this mature
phase, the technology is seamlessly integrated into the architecture of
the workplace.
Thus, within the UbiComp model, there is no computer on my desk because
my desktop is my computer. As today, there is a large white board
on my wall, but with UbiComp, it is active, and can be linked to yours,
which may be 3000 km away. What I see is way less technology. What I get
is way less intrusion (noise, heat, etc.) and way more functionality and
convenience. And with my Pads and Tabs, and the wireless networks that they
employ, I also get far more mobility without becoming a computational "orphan."
UbiVid
UbiVid is the video compliment to UbiComp in that it shares the twin properties
of ubiquity and transparency. In "desktop videoconferencing,"
as it is generally practiced, what we typically see is a user at a desk
talking to someone on a monitor that has a video camera placed on top. Generally,
the video interactions are confined to this single camera-monitor pair.
Figure 1: A Typical Desktop Video Conferencing Configuration
Conferencing is typically channeled through a video camera on
top of a monitor on the user's desktop.
In UbiVid, we break out of this, just as UbiComp breaks out of focusing
all computer-mediated activity on a single desk-top computer. Instead, the
assumption is that there are a range of video cameras and monitors in the
workspace, and that all are available. By having video input and output
available in different sizes and locations, we enable the most important
concept underlying UbiVid: exploiting the relationship between (social)
function and space.
In what follows, we explore the significance of this relationship. We start
by articulating some of the underlying design principles, and then proceed
to work through a number of examples.
Design Principle 1: Preserve function/location relations
for both tele and local activities.
Design Principle 2: Treat electronic and physical "presences"
or visitors the same.
Design Principle 3: Use same social protocols for electronic and physical
social interactions.
Example: Visitor vs. Office Mate
Figure 2 illustrates two scenarios for how an office might be laid out.
The first (a), shows an office with a desk holding a single video monitor
and a visitor's chair. This is typical of the layout that one would find
in most "mediaspace" environments (including our own). This layout,
however, violates design Principles 1 & 2. All video transactions occur
on a single monitor in a fixed position. This not only causes contention
when there are overlapping demands for services (such as when someone wants
to conference while I am watching a video). It also means that location/function
relationships cannot be exploited, as we shall see below.
Figure 2: Desktop Video vs UbiVid
Figure 2(a) shows channeling all video interactions through
a single camera/monitor pair. Figure 2(b) illustrates the UbiVid approach
of distributing functionality. For simplicity, only monitors (shown in black)
are illustrated.
The second layout (b) captures the character of UbiVid. The video monitor
on the desk is for "reading" video documents and doing "up-close"
work with a remote colleague. The monitor for a video "visitor"
is behind the visitor's chair. Furthermore, a monitor for a virtual office
mate is off to the side where an office mate's desk would be.
For simplicity, the figure shows video monitors only. In each case, there
would be a camera and loudspeaker paired with each monitor, to ensure reciprocity.
In addition, one would typically also have one ort more computers (which
may or may not use the same monitor(s) as the video).
In the example, function and space relationships are preserved. The "electronic"
visitor sits where a physical visitor would. Likewise, the virtual office
mate sits where a physical one would. If the equipment is properly placed,
the visitor may well see the office mate, who could see the visitor, etc.
Because of this distributed use of space, contention for resources is reduced
and social conventions can be preserved.
Example: Back-to-Front Videoconferencing
Another example of using spatially distributed video is the implementation
of "back-to-front" videoconferencing at the University of Toronto.
In contrast to traditional videoconferencing rooms, the camera and monitors
are placed at the back of the room, as illustrated in Figure 3.[2]
The intent here is to enable remote participants to "take their place
at the table."
Figure 3: Back-to-Front Videoconferencing
Remote attendees to a meeting take their place at the table
by means of video monitors mounted on the back wall. They see through the
adjacent camera, hear via a microphone, and speak through their monitor's
loudspeaker. The presenter uses the same conventional skills in interacting
with those attending physically and those attending electronically. No new
skills are required.
The scenario shown in the figure illustrates the notion of transparency.
A presentation is being made to five local and three remote participants.
Due to the maintenance of audio and video reciprocity coupled with maintaining
"personal space," the presenter uses the same social mechanisms
in interacting with both local and remote attendees. Stated another way,
even if the presenter has no experience with videoconferencing or technology,
there is no new "user interface" to learn. If someone raises their
hand, it is clear they want to ask a question. If someone looks confused,
a point can be clarified. Rather than requiring the learning new skills,
the design makes use of existing skills acquired from a life time of living
in the everyday world.
Example: Hydra: supporting a 4-way round-table meeting
In this example, we introduce a technique to support a four-way meeting,
where each of the participants is in a different location. It was designed
to capture many of the spatial cues of gaze, head turning, gaze awareness
and turn taking that are found in face-to-face meetings. Consistent with
the design principles outlined above, we do this by preserving the spatial
relationships "around the table."[3] This is
illustrated in Figure 4.
(a)
(b)
Figure 4: Using video "surrogates" to support a 4-way
video conference
Figure (a) shows a 4-way video conference where each of the
three remote participants attends via a video "surrogate." By
preserving the "round-table" relationships illustrated in (b),
conversational acts found in face-to-face meetings, such as gaze awareness,
head turning, etc.. are preserved.
As seen in the left-hand figure, each of the three remote participants are
represented by a small video surrogate. These are the small Hydra
units seen on the desk (Sellen, Buxton & Arnott, 1992). Sitting in front
of the desk is a colleague, Abi Sellen. Each unit provides a unique view
of her for one of the remote participants, and provides her a unique view
of them. The spatial relationship of the participants is illustrated by
the "round-table" in the right-hand figure. Hence, person A, B
and C appear to Abi on the Hydra units to her left, centre and right, respectively.
Likewise, person A sees her to their right, and B to their left, etc.
Collectively, the units shown in the figure mean that Abi has three monitors,
cameras and speakers on her desk. Yet, the combined footprint is less than
that of her telephone. These Hydra units represent a good example of transparency
through ubiquity. This is because each provides a distinct point source
for the voice of each remote participant. As a result, the basis for supporting
parallel conversations is provided. This showed up in a formal study which
compared various technologies for supporting multiparty meetings (Sellen,
1992). The Hydra units were the only technology tested that exhibited the
parallel conversations seen in face-to-face meetings.
The units lend themselves to incorporating proximity sensors that would
enable aside comments to be made in the same way as face-to-face meetings:
by leaning towards the person to whom the aside is being directed. Because
of the gaze awareness that the units provide, the regular checks and balances
of face-to-face meetings would be preserved, since all participants would
be aware that the aside was being made, between whom, and for how long.
None of these every-day speech acts are supported by conventional designs,
yet in this instantiation, they come without requiring any substantially
new skills. There is no "user interface." One interacts with the
video surrogates using essentially the same social skills or conventions
that one would use in the face-to-face situation.
Concept: Video Surrogate: Don't think of the camera as
a camera. Think of it as a surrogate eye. Likewise, don't think of the speaker
as a speaker. Think of it as a surrogate mouth. Integrated into a single
unit, a vehicle for supporting design Principles 1 & 2 is provided.
Our next example pushes even harder on the notion of using video surrogates
to capture important relationships between physical space and social function.
Example: Fly-on-the-wall View from the Door
The physical world occupies real space. Not only is there location and distance
in this space, but social graces are determined by how we move in
this space, such as in approaching one another, or in taking leave. Moving
through physical space involves a continuum, whereas making a connection
via a video link does not. Therefore, with conventional desktop video techniques,
such as illistrated in Figure 1, you are either there or not there, and
when you are there, you are right in my face, you get there abruptly, thereby
violating normal social behaviour.
Figure 5: Maintaining social distance
In establishing contact, one appears by the door and has a from-the-door
view via the camera, monitor and speaker mounted at that location. The social
graces of approach are preserved, and the same social conventions are used
for both physical and electronic visitors.
Figure 5 above shows a UbiVid approach to this problem. When you come to
my office, you come via the door. If you come physically, then all is normal.
If you come electronically, you appear in the monitor by the door, I hear
you from the speaker by the door, and you see me from a wide angle low-resolution
camera by the door. Thus, the glance that you first get is essentially the
same as what you would get through the door. If I am concentrating on something
or someone else, I may not see you or pay attention to you, just as would
be the case if you were walking by the hall (even though I may well hear
that someone is there or has passed by). Appropriate distance is maintained.
If you knock or announce yourself, I may invite you in, in which case you
come in to the "visitor's" chair, i.e., the visitor's monitor
seen in Figure 2. On the other hand, on glancing in, you may well see that
I am busy and choose to come back later (physically or electronically).
This design serves both parties in the interaction. The vistor is saved
the potential mbarassment of intruding in the middle of something, and the
integrity of the personal space of the occupant is preserved.
Example: Door State and Accessibility
The previous example showed the preservation of distance for both electronic
and physical visitors by preserving the social distance to the door. We
can extend this further. That same door controls my accessibility to physical
visitors. If it is open, you are welcome to "pop in." If it is
ajar, you can peep in and determine if I am busy. You will probably knock
if you want to enter. If it is closed, you will knock and wait for a response
before entering. If there is a "Do Not Disturb" sign on the door,
you will not knock, but you might leave a message.
According to Principle 3, so should it be for electronic visitations, regardless
if one is approaching by phone or by video link.
Figure 6 represents the interface, suggested by Abi Sellen, that we use
to transfer these protocols to the electronic domain. With this interface,
one sets one's own accessibility by selecting one of the four door states
shown. One can even leave a "note" on the virtual door in order
to pass on a message to visitors.
Figure 6: Using "door state" to specify accessibility
The figure illustrates a technique for users in a media space
to control their own accessibility following the same approach used in physical
space: by the state of their door. Each one of the selectable door states
allows a different level of accessibility. The specified door state is visible
to potential callers who, likewise, know the implied permissions by analogy
with the physical world.
While preserving the protocols of the physical world by metaphor,
this design, however, still fails to comply fully with Principle 3. The
reason is that while the protocols are parallel, they are not one.
This would be achieved if the physical door itself controlled of
the state of my accessibility for both electronic and physical visitors,
alike. Hence (naturally subject to the ability to override defaults), closing
my physical door could be sensed by the computer and prevent people from
entering physically or electronically (by phone or by video). One action
and one protocol controls all.[4]
Much of the above is based on the notion that the physical location of participants
has an important influence on social interactions in face-to-face meetings.
What we are driving at from a design perspective is that these same cues
can be used or exploited in telepresence. When we talk about distance between
participants, therefore, it is important to distinguish between their physical
distance from me, and the distance between their video surrogate and me.
The latter, rather than the former, is what determines social distance.
Premise: Physical distance and location of your video surrogate
with respect to me carries the same social weight/function/baggage as if
you were physically in your surrogate's location. Furthermore, the assumption
is that this is true regardless of your actual physical distance from me.
Qualification: This equivalence is dependent on appropriate design.
It sets standards and criteria for design and evaluation.
From Appliances to Architecture
Consider the UbiVid equivalent to sitting across the desk from one another,
as illustrated in Figure 7. Here, through rear projection, the remote participant
appears life-size across the desk. What we are trying to capture in this
example is where two people are working together on a joint project, such
as a drawing or budget, which is on the desktop. In implementing this example,
a number of significant points arise.
First, it is not like watching TV. Because of the scale of the image, the
borders of the screen are out of our main cone of vision. The remote person
is defined by the periphery of their silhouette, not by the bezel of a monitor.
Second, by being life size, there is a balance in the weight or power exercised
by each participant.
Third, and perhaps most important, the gaze of the remote participant can
traverse into our own physical space. When the remote party looks down on
their desk, our sense of gaze awareness (see also Ishii, Kobayashi
& Grudin, 1992) gives us the sense that they are looking onto our own
desktop. Their gaze traverses the distance onto our shared workspace, thereby
strengthening the sense of Telepresence.
Figure 7: Face-to-Face
In this scenario, each participant have a computerized desktop
on which the same information is displayed. The intention is to capture
the essence of working across the desk from one-another. Each sees the remote
participant life-size. The video camera (from a Hydra unit) is unobtrusive
on the desk. Particpants interact with the computer using a stylus. When
one participant looks down to their desktop, their eyes seem to project
into the space of the other, thereby strengthening the sense of Telepresence.
While there is a considerable amount of technology involved, it is integrated
into the architectural ecology. What one gets is lots of service and lots
of space, not lots of gear and appliances.
What is central to this example is the contrast between the simplicity and
naturalness of the environment and the potency of its functionality. In
keeping with the principle of invisibility, a powerful, non intrusive work
situation has been created.
Design Principle 4: The box into which we are designing
our solutions is the room in which you work/play/learn, not a box that sits
on your desk. That is the difference between the ecological design of Ubiquitous
Media and the design of appliances.
Active Sensing and the Active Office: UbiComp Meets UbiVid
The earlier example of having the computer sense the state of our physical
door breaks set with conventional practice, yet is a natural outgrowth of
both UbiComp and UbiVid. It bridges the gap between human-human and human-computer
interaction.
Observation: A door is just as legitimate input device
to a computer as are a mouse or a keyboard.
The ability to make computers more "aware" of their surroundings
is an important part of our work. We want to explore the degree to which
sensed potentials can mapped into system control signals. Consider this:
a computer is made up of thousands of switches, yet AI notwithstanding,
a motion sensing light switch is smarter than any of them since it has the
ability to sense motion and turn a light on when someone is present.
When you walk up to your computer, does the screen saver stop and the
working windows reveal themselves? Does it even know if your are there?
How hard would it be to change this? Is it not ironic that, in this regard,
a motion-sensing light switch is "smarter" than any of the switched
in the computer, AI nonwithstanding?
In addition to door sensors, motion sensors, and the like, the technologies
of UbiVid expand the potential for interaction in the UbiComp environment.
The same cameras that I use for video conferencing can give my computer
"eyes." The same microphone through which I speak to my colleagues
can also provide my computer with an "ear." The displays on which
I view my video may also display data, and vice versa: when the world is
digital, video and data are one.
Design Principle 5: Every device used for human-human interaction
(cameras, microphones, etc.) are legitimate candidates for human-computer
interaction (and often simultaneously).
My desk-top camera could sense if I am at my desk. If I am not, but the
door-way camera senses that I am in the room, then the computer could switch
from visual output to audio output in communicating to me. Also, since it
is analyzing the input to the microphone (through simple signal detection),
it knows if I am speaking or not. If so, it will wait until I am finished
so that it doesn't interrupt.
This expanded repertoire of technologies can lay the basis for a far more
seamless interface between the physical and electronic worlds. Krueger (1983,
1991) has shown that video cameras can be effective input devices for controlling
computer systems. Central to his approach (as opposed to that commonly seen
in virtual reality systems) is that it is non intrusive. One need not wear
any special gloves or sensors. The system sees and understands hand gesture
much in the same way that people do: by watching the hands.
Figure 8: Myron Krueger's Videodesk:
The user's hands are "seen" by the computer and superimposed
on the display. The system can recognize each hand, its position and its
shape (open, closed, pointing, etc.). Based on this, one can manipulate
objects in the scene. In this case, a user is reorienting a square.
It is not just the link between human and machine that these technologies
facilitate. It is also the provision of a more seamless link between the
artifacts of the physical and electronic worlds. As technologies become
more "intimate," or close to the person, they will increasingly
have to provide a bridge between these two worlds. Small portable tab-sized
computers may more resemble a camera than a calculator, for example.
One of the best examples of using these media to provide such a bridge is
the Digital Desk of Wellner (1992), illustrated in Figure 9. This
system goes beyond both desktop computers and the desktop metaphor. In this
case, the desktop is the computer.
As shown in the figure, there is a projector and a camera mounted over the
desk. The former projects the computer's display onto the desktop. The camera
enables the computer to "see" what is on the desktop. Hence, electronic
documents can be projected, as can active widgets such as a calculator or
a browser. And, like the Krueger example, the camera enables the computer
to see the actions of the hands on the desk, and to use this as input. It
also enables the computer to "see" documents and objects on the
desktop. Here again the potential exists for recognition. In the working
prototype, for example, the camera can be used to scan alphanumeric data
to which optical character recognition techniques are applied, thereby enabling
the computer to "read" what is on the desk.
Figure 9: The Digital Desk (Wellner, 1992)
With this system, electronic documents are projected onto the
desktop. Similarly, a camera enables the computer to see what is on the
desktop. It can see documents, and "read" them using optical character
recognition (OCR) techniques. It can also "See" the user's hands
and recognize gestures, such as pointing, selection, and activating graphical
"buttons" of devices projected onto the desk surface.
Summary and Conclusions
We have hit the complexity barrier. Using conventional design techniques,
we cannot significantly expand the functionality of systems without passing
users' threshold of frustration. Rather than adding complexity, technology
should be reducing it, and enhancing our ability to function in the emerging
world of the future.
The approach to design embodied in the Ubiquitous Media approach represents
a break from previous practice. It represents a shift to design that builds
upon users' existing skills, rather than demanding the learning of new ones.
It is a mature approach to design that breaks out of the "solution-in-a-box"
appliance mentality that dominates current practice. Like good architecture
and interior design, it is comfortable, non intrusive and functional.
To reap the benefits that this approach offers will require a rethinking
of how we define, teach and practice our science. Following the path outlined
above, the focus of our ongoing research is to apply our skills in technology
and social science to both refine our understanding of design, and establish
its validity in those terms that are the most important: human ones.
Acknowledgments
The ideas developed in this essay have evolved over countless discussions
with colleagues at Rank Xerox EuroPARC, Xerox PARC and the Ontario Telepresence
Project. To all of those who have helped make these such stimulating environments,
I am very grateful. I would like to especially acknowledge the contributions
of Abi Sellen, Sara Bly, Steve Harrison, Mark Weiser, Brigitta Jordan and
Bill Gaver. In addition, I would like to thank barbara Whitmer, who made
many useful comments on the manuscript.
The research discussed in this paper has been supported by the Ontario Telepresence
Project, Xerox PARC and the Natural Sciences and Engineering Research Council
of Canada. This support is gratefully acknowledged.
References
Bly, S., Harrison, S. & Irwin, S. (1993). Media Spaces: bringing people
together in a video, audio and computing environment. Communications
of the ACM, 36(1), 28-47.
Fields, C.I. (1983). Virtual space teleconference system. United States
Patent 4,400,724, August 23, 1983.
Gaver, W., Moran, T., MacLean, A., Lövstrand, L., Dourish, P., Carter,
K. & Buxton, W. (1992). Realizing a video environment: EuroPARC's RAVE
System. Proceedings of CHI '92, 27-35.
Ishii, H., Kobayashi, M. & Grudin, J. (1992). Integration of inter-personal
space and shared workspace: Clarboard design and experiments. Proceedings
of CSCW '92, 33 - 42.
Krueger, Myron, W. (1983). Artificial Reality. Reading: Addison-Wesley.
Krueger, Myron, W. (1991). Artificial Reality II. Reading: Addison-Wesley.
Mantei, M., Baecker, R., Sellen, A., Buxton, W., Milligan, T. & Welleman,
B. (1991). Experiences in the use of a media space. Proceedings of CHI
'91, ACM Conference on Human Factors in Software, 203-208.
Sellen, A. (1992). Speech patterns in video mediated conferences. Proceedings
of CHI '92, ACM Conference on Human Factors in Software,, 49-59.
Sellen, A., Buxton, W. & Arnott, J. (1992). Using spatial cues to improve
videoconferencing. Proceedings of CHI '92, 651-652. Also videotape
in CHI '92 Video Proceedings.
Stults, R. (1986). Media Space. Systems Concepts Lab Technical Report. Palo
Alto, CA: Xerox PARC.
Weiser, M. (1991). The computer for the 21st century. Scientific American,
265(3), 94-104.
Wellner, P. (1992). The DigitalDesk Calculator: Tangible manipulation on
a desktop display. Proceedings of the Fourth Annual Symposium on User Interface
Software and Technology, 27-33.
[1] Author's current address: W. Buxton, Head, User
Interface Research, Alias | Wavefront Inc., 110 Richmond St. E., Toronto,
Ontario, Canada MM5C 1P1. Fax: 416-861-8802. Email: buxton@aw.sgi.com.
[2] In fact, the room also supports traditional "front-to-back
conferencing, which just pushes the issue of ubiquity even further.
[3] This idea of using video surrogates in this way for
multiparty meetings turns out not to be new. After implementing it ourselves,
we found that it had been proposed by Fields (1983).
[4] In reality, it is probably wrong to hard-wire such
protocols into a system. The meaning of door state is culture specific,
for example. As the ability of a system to sense the context within which
it is to react increases, so must the quality and flexibility of the tools
for user tailoring of those actions. The examples that we give are to establish
another way of thinking about systems. They are not intended to provide
some dogma as to specific designs.