Human Computer Interaction (CS408)
Lecture 15. Interaction Paradigms
As the aim of this lecture is to introduce you the study of Human Computer
Interaction, so that after studying this you will be able to:
Describe WIMP interfaces in detail
Discuss different interaction paradigms
We have briefly discussed about the WIMP interfaces in last lecture. Today we will
discuss WIMP interfaces in detail.
The WIMP Interfaces
In our last lecture we have already discussed the four key features of the WIMP
interface that give it its name windows, icons, pointers and menus and today we
will discuss these in greater detail. There are also many additional interaction objects
and techniques commonly used in WIMP interfaces, some designed for specific
purposes and others more general. Our discussion will cover the toolbars, menus,
buttons, palettes and dialog boxes.
Together, these elements of the WIMP interfaces are called widgets, and they
comprise the toolkit for interaction between user and system.
Windows are areas of the screen that behave as if they were independent terminals in
their own right. A window can usually contain text or graphics, and can be moved or
resized. More than one window can be on a screen at once, allowing separate tasks to
be visible at the same time. Users can direct their attention to the different windows as
they switch from one thread of work to another.
If one window overlaps the other, the back window is partially obscured, and then
refreshed when exposed again. Overlapping windows can cause problems by
obscuring vital information, so windows may also be tiled, when they adjoin but do
not overlap each other. Alternatively, windows may be placed in a cascading fashion,
where each new window is placed slightly to the left and below the previous window.
In some systems this layout policy is fixed, in others the user can select it.
Usually windows have various things associated with them that increase their
usefulness. Scrollbars are one such attachment, allowing the user to move the contents
of the window up and down, or from side to side. This makes the window behave as if
it were a real window onto a much larger world, where new information is brought
into view by manipulating the scrollbars.
There is usually a title bar attached to the top of a window, identifying it to the user,
and there may be special boxes in the corners of the window to aid resizing, closing,
or making as large as possible. Each of these can be seen in the figure.
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In addition, some systems allow windows within windows. For example, in Microsoft
Office applications, such as Excel and Word, each application has its own window
and then within this each document has a window. It is often possible to have
different layout policies within the different application windows.
Windows can be closed and lost forever, or they can be shrunk to some very reduced
representation. A small picture is used to represent a closed window, and this
representation is known as an icon. By allowing icons, many windows can be
available on the screen at the same time, ready to be expanded to their full size by
clicking on the icon. Shrinking a window to its icon is known as iconifying the
window. When a user temporarily does not want to follow a particular thread of
dialog, he can suspend that dialog by iconifying the window containing the dialog.
The icon saves space on the screen and serves as a remainder to the user that he can
subsequently resume the dialog by opening up the window. Figure shows a few
examples of icons used in a typical windowing system (Microsoft).
Icons can also be used to represent other aspects of the system, such as a wastebasket
for throwing unwanted files into, or various disks, programs or functions, that are
accessible to the user. Icon can take many forms: they can be realistic representation
of the objects that they stand for, or they can be highly stylized. They can even be
arbitrary symbols, but these can be difficult for users to interpret.
The Pointer is an important component of the WIMP interface, since the interaction
style required by WIMP relies very much on pointing and selecting things such as
icons. The mouse provides an input device capable of such tasks, although joysticks
and trackballs are other alternatives. The user is presented with a cursor on the screen
that is controlled by the input device. A verity of pointer cursors is shown in figure.
The different shape of cursor are often used to distinguish modes, for example the
normal pointer cursor maybe an arrow, but change to change to cross-hairs when
drawing a line. Cursors are also used to tell the user about system activity, for
example a watch or hourglass cursor may be displayed when the system s busy
reading a file.
Pointer cursors are like icons, being small bitmap images, but in addition all cursors
have a hot-spot, the location to which they point.
The last main feature of the windowing system is the menu, an interaction technique
that is common across many non-windowing systems as well. A menu presents a
choice of operations or services that can be performed by the system at a given time.
As we discussed our ability to recall information is inferior to our ability to recognize
it from some visual cue. Menus provide information cues in the form of an ordered
list of operations that can be scanned. This implies that the names used for the
commands in the menu should be meaningful and informative.
The pointing device is used to indicate the desired option. As the pointer moves to the
position of a menu item, the item is usually highlighted to indicate that it is the
potential candidate for selection. Selection usually requires some additional user
action, such as pressing a button on the mouse that controls the pointer cursor on the
screen or pressing some special key on the keyboard. Menus are inefficient when they
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have too many items, and so cascading menus are utilized, in which item selection
opens up another menu adjacent to the item, allowing refinement of the selection.
Several layers of cascading menus can be used.
The main menu can be visible to the user all the time, as a menu bar and submenus
can be pulled down or across from it upon request. Menu bars are often placed at the
top of the screen or at the top of each window. Alternative includes menu bars along
one side of the screen, or even placed amongst the windows in the main `desktop'
area. Websites use a variety of menu bar locations, including top, bottom and either
side of the screen. Alternatively, the main menu can be hidden and upon request it
will pop up onto the screen. These pop-up menus are often used to present context-
sensitive options, for example allowing one to examine properties of particular on-
screen objects. In some systems they are also used to access more global actions when
the mouse is depressed over the screen background.
Pull-down menus are dragged down from the title at the top of the screen, by moving
the mouse pointer into the title par area and pressing the button. Fall-down menus are
similar, except that the menu automatically appears when the mouse pointer enters the
title bar, without the user having to press the button. Some menus explicitly asked to
go away. Pop up menus appear when a particular region of the screen, may be
designated by an icon, is selected, but they only stay as long as the mouse button is
Another approach to menu selection is to arrange the options in a circular fashion.
The pointer appears in the center of the circle, and so there is the same distance to
travel to any of the selections. This has the advantages that it is easier to select items,
since they can each have a larger target area, and that the selection time for each item
is the same, since the pointer is equidistant from them all. However, these pie menus
take up more screen space and are therefore less common in interface.
The major problems with menus in general are deciding what items to include and
how to group those items. Including too many items makes menus too long or creates
too many of them, whereas grouping causes problems in that items that relate to the
same topic need to come under the same heading, yet many items could be grouped
under more than one heading. In pull-down menus the menu label should be chosen to
reflect the function of the menu items, and items grouped within menus by function.
These groupings should be consistent across applications so that the user can transfer
learning to new applications. Menu items should be ordered in the menu according to
importance and frequency of use, and appropriate functionalities should be kept apart
to prevent accidental selection of the wrong function, with potentially disastrous
Menus often offer keyboard accelerators, key combinations that have the same effect
as selecting the menu item. This allows more expert users, familiar with the system, to
manipulate things without moving off the keyboard, which is often faster. The
accelerators are often displayed alongside the menu item so that frequent use makes
Buttons are individual and isolated regions within display that can be selected by the
user to invoke specific operations. These regions are referred to as buttons because
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they are purposely made to resemble the push buttons you would find on a control
panel. `Pushing' the button invokes a command, the meaning of which is usually
indicated by a textual label or a small icon.
Buttons can also be used to toggle between two states, displaying status information
such as whether the current font is italicized or not in a word processor, or selecting
options on a web form. Such toggle buttons can be grouped together to allow a user to
select one feature form a set of mutually exclusive options, such as the size in points
of the current font. These are called radio buttons.
It a set of options is not mutually exclusive, such as font characteristics like bold,
italic and underlining, and then a set of toggle buttons can be used to indicate the
on/off status of the options. This type of collection of buttons is sometimes referred to
as check boxes
Many systems have a collection of small buttons, each with icons, placed at the top or
side of the window and offering commonly used functions. The function of this
toolbar is similar to a menu bar, but as the icons are smaller than the equivalent text
more functions can be simultaneously displayed. Sometimes the content of the toolbar
is fixed, but often users can customize it, either changing which functions area made
available, or choosing which of several predefined toolbars is displayed
In many application programs, instructions can either one of several modes. The
defining characteristic of modes is that the interpretation of actions, such as
keystrokes or gestures with the mouse, changes as the mode change. For example,
using the standard UNIX text editor vi, keystrokes can be interpreted either as
operations to insert characters in the document or as operations to perform file
manipulation. Problems occur if the user is not aware of the current mode. Palettes are
a mechanism for making the set of possible modes and the active mode visible to the
user. A palette is usually a collection of icons that are reminiscent of he purpose of the
various modes. An example in a drawing package would be a collection of icons to
indicate the pixel color or pattern that is used to fill in objects, much like an artist's
palette for paint.
Some systems allow the user to create palettes from menus or toolbars. In the case of
pull-down menus, the user may be able `tear off' the menu, turning it into a palette
showing the menu items. In the case of toolbars, he may be able to drag the toolbar
away from its normal position and place it anywhere on the screen. Tear-off menus
are usually those that are heavily graphical anyway, for example line style of color
selection in a drawing package.
Dialog boxes are information windows used by the system to bring the user's
attention to some important information, possibly an error or a warning used to
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prevent a possible error. Alternatively, they are used to invoke a sub dialog between
user and system for a very specific task that will normally be embedded within some
larger task. For example, most interactive applications result in the user creating some
file that will have to be named and stored within the filing system. When the user or
the file and indicate where it is to be located within the filing system. When the save
sub dialog is complete, the dialog box will disappear. Just as windows are used to
separate the different threads of user-system dialog, so too are dialog boxes used to
factor out auxiliary task threads from the main task dialog.
We believe that we now build interactive systems that are more usable than those built
in the past. We also believe that there is considerable room for improvement in
designing more usable systems in the future. The great advances in computer
technology have increased the power of machines and enhanced the bandwidth of
communication between human and computer. The impact of the technology alone,
however, is not sufficient to enhance its usability. As our machines have become
more powerful, they key to increased usability has come from the creative and
considered application of the technology to accommodate and augment the power of
the human. Paradigms for interaction have for the most part been dependent upon
technological advances and their creative application to enhance interaction.
By interaction paradigm, it is meant a particular philosophy or way of thinking about
interaction design. It is intended to orient designers to the kinds of questions they
need to ask. For many years the prevailing paradigm in interaction design was to
develop application for the desktop intended to be used by single user sitting in
front of a CPU, monitor, keyboard and mouse. A dominant part of this approach was
to design software applications that would run using a GUI or WIMP interface.
Recent trend has been to promote paradigms that move beyond the desktop. With the
advent of wireless, mobile, and handheld technologies, developers started designing
applications that could be used in a diversity of ways besides running only on an
individual's desktop machine.
We will discuss different paradigms here.
In the 1940s and 1950s, the significant advances in computing consisted of new
hardware technologies. Mechanical relays were replaced by vacuum electron tubes.
Tubes were replaced by transistors, and transistors by integrated chips, all of which
meant that the amount of sheer computing power was increasing by orders of
magnitude. By the 1960s it was becoming apparent that the explosion of growth in
computing power would be wasted if there were not an equivalent explosion of ideas
about how to channel that power. One of the leading advocates of research into
human-centered applications of computer technology was J.C.R Licklider, who
became the director of the Information Processing Techniques Office of the US
Department of Defense's Advanced Research Agency (ARPA). It was Licklider's
goal to finance various research centers across the United States in order to encourage
new ideas about how best to apply the burgeoning computing technology.
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One of the major contributions to come out of this new emphasis in research was the
concept of time-sharing, in which a single computer could support multiple users.
Previously, the human was restricted to batch sessions, in which complete jobs were
submitted on punched cards or paper tape to an operator who would then run them
individually on the computer. Time-sharing systems of the 1960s made programming
a truly interactive venture and brought about a subculture of programmers known as
`hackers' single-minded masters of detail who took pleasure in understanding
complexity. Though the purpose of the first interactive time-sharing systems was
simply to augment the programming capabilities of the early hackers, it marked a
significant stage in computer applications for human use.
Video display units
As early as the mid-1950s researchers were experimenting with the possibility of
presenting and manipulating information from a computer in the form of images on a
video display unit (VDU). These display screens could provide a more suitable
medium than a paper printout for presenting vast quantities of strategic information
for rapid assimilation. It was not until 1962, however, when a young graduate student
at the Massachusetts Institute of Technology (MIT), Ivan Sutherland, astonished the
established computer science community with the Sketchpad program, that the
capabilities of visual images were realized.
Sketchpad demonstrated two important ideas. First, computers could be used for more
than just data processing. They could extend the user's ability to abstract away from
some levels of detail, visualizing and manipulating different representations of the
same information. Those abstractions did not have to be limited to representations in
terms of bit sequences deep within the recesses of computer memory. Rather, the
abstraction could be make truly visual. To enhance human interaction, the information
within the computer was made more amenable to human consumption. The computer
was made to speak a more human language, instead of the human being forced to
speak more like a computer. Secondly, Sutherland's efforts demonstrated how
important the contribution of one creative mind could be to the entire history of
Dougles Engelbart's ambition since the early 1950s was to use computer technology
as a means of complementing human problem-solving activity. Engelbart's idea as a
graduate student at the University f California at Berkeley was to use the computer to
teach humans. This dream of naÔve human users actually learning from a computer
was a stark contrast to the prevailing attitude of his contemporaries that computers
were purposely complex technology that only the intellectually privileged were
capable of manipulating.
Programming toolkits provide a means for those with substantial computing skills to
increase their productivity greatly. But Engelbart's vision was not exclusive to the
computer literate. The decade of the 1970s saw the emergence of computing power
aimed at the masses, computer literate or not. One of the first demonstrations that the
powerful tools of the hacker could be made accessible to the computer novice was a
graphics programming language for children called LOGO. The inventor, Seymen
Papert, wanted to develop a language that was easy for children to use. He and his
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colleagues from MIT and elsewhere designed a computer-controlled mechanical turtle
that dragged a pen along a surface to trace its path. In the early 1970s Alan Kay view
of the future of computing was embodied in small, powerful machines, which were
dedicated to single users, that is personal computers. Together with the founding team
of researchers at the Xerox Palo Alto Research Center, Kay worked on incorporating
a powerful and simple visually based programming environment, Smalltalk, for the
personal computing hardware that was just becoming feasible. As technology
progresses, it is now becoming more difficult to distinguish between what constitutes
a personal computer, or workstation, and what constitutes a mainframe.
Window systems and the WIMP interface
With the advent and immense commercial success of personal computing, the
emphasis for increasing the usability of computing technology focused on addressing
the single user who engaged in a dialog with the computer in order to complete some
work. Humans are able to think about more than one thing at a time, and in
accomplishing some piece of work, they frequently interrupt their current train of
thought to pursue some other related piece of work. A personal computer system
which forces the user to progress in order through all of the tasks needed to achieve
some objective, from beginning to end without any diversions, does not correspond to
that standard working pattern. If the personal computer is to be an effective dialog
partner, to must be as flexible in its ability to change the topic as the human is.
But the ability to address the needs of a different user task is not the only requirement.
Computer systems for the most part react to stimuli provided by the user, so they are
quite amenable to a wandering dialog initiated by the user. As the ser engages in more
than one plan of activity over a stretch of time, it becomes difficult for him to
maintain the status of the overlapping threads of activity.
Interaction based on windows, icons, menus, and pointers--the WIMP interface--is
now commonplace. These interaction devices first appeared in the commercial
marketplace in April 1981, when Xerox Corporation introduced the 8010 Star
Metaphor is used quite successfully to teach new concepts in terms of ones, which are
already understood. It is no surprise that this general teaching mechanism has been
successful in introducing computer novices to relatively foreign interaction
techniques. Metaphor is used to describe the functionality of many interaction
widgets, such as windows, menus, buttons and palettes. Tremendous commercial
successes in computing have arisen directly from a judicious choice of metaphor. The
Xerox Alto and Star were the first workstations based on the metaphor of the office
desktop. The majority of the management tasks on a standard workstation have to do
with the file manipulation. Linking the set of tasks associated with file manipulation
to the filing tasks in a typical office environment makes the actual computerized tasks
easier to understand at first. The success of the desktop metaphor is unquestionable.
Another good example in the personal computing domain is the widespread use of the
spreadsheet for accounting and financial modeling.
Very few will debate the value of a good metaphor for increasing the initial
familiarity between user and computer application. The danger of a metaphor is
usually realized after the initial honeymoon period. When word processors were first
introduced, they relied heavily on the typewriter metaphor. The keyboard of a
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computer closely resembles that of a standard typewriter, so it seems like a good
metaphor from any typewriter. For example, the space key on a typewriter is passive,
producing nothing on the piece of paper and just moving the guide further along the
current line. For a typewriter, a space is not a character. However, for a word
processor, the blank space is a character, which much be inserted within a text just as
any other character is inserted. So an experienced typist is not going to be able to
predict his experience with a preliminary understanding of a word processor.
Another problem with a metaphor is the cultural bias that it portrays. With the
growing internationalization of software, it should not be assumed that a metaphor
will apply across national boundaries. A meaningless metaphor will only add another
layer of complexity between the user and the system.
In the early 1980s as the price of fast and high-quality graphics hardware was steadily
decreasing, designers were beginning to see that their products were gaining
popularity as their visual content increased. As long as the user-system command line
prompt computing was going to stay within the minority population of the hackers
who reveled in the challenge of complexity. In a standard command line interface, the
only way to get any feedback on the results of previous interaction is to know that you
only have to ask for it and to know how to ask for it. Rapid visual and audio feedback
on a high-resolution display screen or through a high-quality sound system makes it
possible to provide evaluative information for every executed user action.
Rapid feedback is just one feature of the interaction technique known as direct
manipulation. Ben Shneiderman is attributed with coining this phrase in 1982 to
describe the appeal of graphics-based interactive systems such as Sketchpad and the
Xerox Alto and Star. He highlights the following features of a direct manipulation
∑ visibility of the objects of interest
incremental action at the interface with rapid feedback on all actions
reversibility of all actions, so that users are encouraged to explore without
syntactic correctness of all actions, so that every user action is a legal
replacement of complex command language with actions to manipulate
directly the visible objects.
The first real commercial success which demonstrated the inherent usability of direct
manipulation interfaces for the general public was the Macintosh personal computer,
introduced by Apple Computer, Inc. in 1984 after the relatively unsuccessful
marketing attempt in the business community of the similar but more pricey Lisa
computer. The direct manipulation interface for the desktop metaphor requires that the
documents and folders are made visible to the user as icons, which represent the
underlying files and directories. An operation such as moving a file from one
directory to another is mirrored as an action on the visible document, which is picked
and dragged along the desktop from one folder to the next.
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Language versus action
Whereas it is true that direct manipulation interface make some tasks easier to
perform correctly, it is equally true that some tasks are more difficult, if not
impossible. Contrary to popular wisdom, it is not generally true that action speak
louder than words. The image, projected for direct manipulation was of the interface
as a replacement for the underlying system as the world of interest to the user. Actions
performed at the interface replace any need to understand their meaning at any deeper,
system level. Another image is of the interface s the interlocutor or mediator between
the user and the system. The user gives the interface instructions and it is then the
responsibility of the interface to see that those instructions are carried out. The user-
system communication is by means of indirect language instead of direct actions.
We can attach two meaningful interpretations to this language paradigm. The first
requires that the user understands how the underlying system functions and the
interface as interlocutor need not perform much translation. In fact, this interpretation
of the language paradigm is similar to the kind of interaction, which existed before
direct manipulation interfaces were around. In a way, we have come full circle.
The second interpretation does not require the user to understand the underlying
system's structure. The interface serve a more active role, as it must interpret between
the intended operation as requested by the user and the possible system operations
that must be invoked to satisfy that intent. Because it is more active, some people
refer to the interface as an agent in these circumstances. This kind of language
paradigm can be seen in some internal system database, but you would not know how
that information is organized.
Whatever interpretation is attached to the language paradigm, it is clear that it has
advantages and disadvantages when compared with the action paradigm implied by
direct manipulation interfaces. In the action paradigm, it is often much easier to
perform simple tasks without risk o certain classes or error. For example, recognizing
and pointing to an object reduces the difficulty of identification and the possibility of
misidentification. On the other hand, more complicated tasks are often rather tedious
to perform in the action paradigm, as they require repeated execution of the same
procedure with only minor modification. In the language paradigm, there is the
possibility describing a generic procedure once and then leaving it to be executed
without further user intervention.
The action and language paradigms need not be completely separate. In the above
example two different paradigms are distinguished by saying that generic and
repeatable procedures can be described in the language paradigm and not in the action
paradigm. An interesting combination of the two occurs in programming by example
when a user can perform some routine tasks in the action paradigm and the system
records this as a generic procedure. In a sense, the system is interpreting the user's
actions as a language script that it can then follow.
In 1945, Vannevar Bush, then the highest-ranking scientific administrator in the US
war effort, published an article entitled `As We May Think' in The Atlantic Monthly.
Bush was in charge of over 6000 scientists who had greatly pushed back the frontiers
of scientific knowledge during the Second World War. He recognized that a major
drawback of these prolific research efforts was that it was becoming increasingly
difficult to keep in touch with the growing body of scientific knowledge in the
literature. In his opinion, the greatest advantages of this scientific revolution were to
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be gained by those individuals who were able to keep abreast of an ever-increasing
flow of information. To that end, he described an innovative and futuristic
information storage and retrieval apparatus the memex , which was constructed
with technology wholly existing in 1945 and aimed at increasing the human capacity
to store and retrieve, connected pieces of knowledge by mimicking our ability to
create random associative links.
An unsuccessful attempt to create a machine language equivalent of the memex on
early 1960s computer hardware led Nelson on a lifelong quest to produce Xanadu, a
potentially revolutionary worldwide publishing and information retrieval system
based on the idea of interconnected, non-linear text and other media forms. A
traditional paper is read from beginning to end, in a linear fashion. But within that
text, there are often ideas or footnotes that urge the reader to digress into richer topic.
The linear format for information does not provide much support for this random and
associated browsing task. What Bush's memex suggested was to preserve the non-
linear browsing structure in the actual documentation. Nelson coined the phrase
hypertext in the mid 1960s to reflect this non-linear text structure.
The majority of interactive systems still use the traditional keyboard and a pointing
device, such as a mouse, for input and are restricted to a color display screen with
some sound capabilities for output. Each of these input and output devices can be
considered as communication channels for the system and they correspond to certain
human communication channels. A multi-modal interactive system is a system that
relies on the use of multiple human communication channels. Each different channel
for the user is referred to as a modality of interaction. In this sense, all interactive
systems can be considered multi-model, for human have always used their visual and
haptic channels in manipulating a computer. In fact, we often use our audio channel to
hear whether the computer is actually running properly.
However, genuine multi-modal systems rely to an extent on simultaneous use of
multiple communication channels for both input and output. Humans quite naturally
process information by simultaneous use of different channels.
Computer-supported cooperative work
Another development in computing in the 1960s was the establishment of the first
computer networks, which allowed communication between separate machines.
Personal computing was all about providing individuals with enough computing
power so that they were liberated from dumb terminals, which operated on a time-
sharing systems. It is interesting to note that as computer networks become
widespread, individuals retained their powerful workstations but now wanted to
reconnect themselves to the rest of the workstations in their immediate working
environment, and even throughout the world. One result of this reconnection was the
emergence of collaboration between individuals via the computer called computer
supported cooperative work, or CSCW.
The main distinction between CSCW systems and interactive systems designed for a
single user is that designer can no longer neglect the society within which any single
user operates. CSCW systems are built to allow interaction between humans via the
computer and so the needs of the many must be represented in the one product. A fine
example of a CSCW system is electronic mail email yet another metaphor by
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which individuals at physically separate locations can communicate via electronic
messages that work in a similar way to conventional postal systems.
The World Wide Web
Probably the most significant recent development interactive computing is the World
Wide Web, often referred to as just the web, or WWW. The web is built on top of the
Internet, and offers an easy to use, predominantly graphical interface to information,
hiding the underlying complexities of transmission protocols, addresses and remote
access to data.
The Internet is simply a collection of computers, each linked by any sort of data
connections, whether it be slow telephone line and modem or high-bandwidth optical
connection. The computers of the Internet all communicate using common data
transmission protocols and addressing systems. This makes it possible for anyone to
read anything from anywhere, in theory, if it conforms to the protocol. The web builds
on this with its own layer of network protocol, a standard markup notation for laying
out pages of information and a global naming scheme. Web pages can contain text,
color images, movies, sound and, most important, hypertext links to other web pages.
Hypermedia documents can therefore be published by anyone who has access to a
computer connected to the Internet.
In the late 1980s, a group of researchers at Xerox PARC led by Mark Weiser, initiated
a research program with the goal of moving human-computer interaction away from
the desktop and out into our everyday lives. Weiser observed.
The most profound technologies are those that disappear. They weave themselves into
the fabric of everyday life until they are indistinguishable from it.
These words have inspired a new generation of researchers in the area of ubiquitous
computing. Another popular term for this emerging paradigm is pervasive computing,
first coined by IBM. The intention is to create a computing infrastructure that
permeates our physical environment so much that we do not notice the computer may
longer. A good analogy for the vision of ubiquitous computing is the electric motor.
When the electric motor was first introduced, it was large, loud and very noticeable.
Today, the average household contains so many electric motors that we hardly ever
notice them anymore. Their utility led to ubiquity and, hence, invisibility.
Sensor-based and context-aware interaction
The yard-scale, foot-scale and inch-scale computers are all still clearly embodied
devices with which we interact, whether or not we consider them `computers'. There
are an increasing number of proposed and existing technologies that embed
computation even deeper, but unobtrusively, into day-to-day life. Weiser's dream was
computers anymore', and the term ubiquitous computing encompasses a wide range
from mobile devices to more pervasive environments.
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