DATA DISPLAY
Data display refers to computer output of data to
a user, and assimilation of information from such outputs. Some kind of
display output is needed for all information handling tasks. Data display
is particularly critical in monitoring and control tasks. Data may be output
on electronic displays, or hardcopy printouts, or other auxiliary displays
and signaling devices including voice output, which may alert users to
unusual conditions.
In this discussion, data are considered to be display elements related
to a user's information handling task.
Displayed data might consist of stock market quotations, or the
current position of monitored aircraft, or a page
of text, or a message from another user. Displayed data might provide
guidance to a user in performing a maintenance task, or might provide instruction
to a user who is trying to learn mathematics or history.
There might be some display elements that themselves do not constitute
task-related data. Those elements include labels, prompts, computer-generated
advisory messages and other guidance that helps a user interact with a
computer system. Although such user guidance display features are sometimes
mentioned here in connection with data display, they are discussed more
extensively in Section 4 of these guidelines.
In general, somewhat less is known about data display,
and information assimilation by the user, than about data entry. In current
information system design, display formatting is an art. Guidelines are
surely needed. But these guidelines may simply serve to help a designer
become more proficient in the art.
It must be recognized that guidelines cannot tell a designer what
the specific contents of a display should be, but only how those contents
should be presented. The specific data that must be displayed can only
be determined through a careful task analysis to define the user's information
requirements.
For effective task performance, displayed data must
be relevant to a user's needs. An early statement (Smith, 1963b, pages
296-297) of the need for relevance in data display, although written before
common adoption of gender-free wording, otherwise seems valid still: When
we examine the process of man-computer communication from the human point
of view, it is useful to make explicit a distinction which might be described
as contrasting "information" with "data." Used in this sense, information
can be regarded as the answer to a question, whereas data are the raw materials
from which information is extracted. A man's questions may be vague, such
as, "What's going on here?" or "What should I do now?" Or they may be much
more specific. But if the data presented to him are not relevant to some
explicit or implicit question, they will be meaningless. . . . What the
computer can actually provide the man are displays of data. What information
he is able to extract from those displays is indicated by his responses.
How effectively the data are processed, organized, and arranged prior to
presentation will determine how effectively he can and will extract the
information he requires from his display. Too frequently these two terms
data and information are confused, and the statement, "I need more information,"
is assumed to mean, "I want more symbols." The reason for the statement,
usually, is that the required information is not being extracted from the
data. Unless the confusion between data and information is removed, attempts
to increase information in a display are directed at obtaining more data,
and the trouble is exaggerated rather than relieved.
Certainly this distinction between data and information
should be familiar to psychologists, who must customarily distinguish between
a physical stimulus (e.g., "intensity" of a light) and its perceived effect
("brightness"). The distinction is not familiar to system designers, however,
although the issue itself is often addressed. In the following description
of what has been called the "information explosion", notice how the terms
data and information are used interchangeably, confounding an otherwise
incisive and lively analysis by Martin (1973, page 6): The sum total of
human knowledge changed very slowly prior to the relatively recent beginnings
of scientific thought. But it has been estimated that by 1800 it was doubling
every 50 years; by 1950, doubling every 10 years; and by 1970, doubling
every 5 years.
This is a much greater growth rate than
an exponential increase. In many fields, even one as old as medicine, more
reports have been written in the last 20 years than in all prior human
history. And now the use of the computer vastly multiplies the rate at
which information can be generated. The weight of the drawings of a jet
plane is greater than the weight of the plane. The computer files of current
IBM customer orders contain more than 100 billion bits of information --
more than the information in a library of 50,000 books. For man, this is
a hostile environment. His mind could no more cope with this deluge of
data, than his body could cope with outer space. He needs protection. The
computer -- in part the cause of the problem -- is also the solution to
the problem. The computer will insulate man from the raging torrents of
information that are descending upon him. The information of the computerized
society will be gathered, indexed, and stored in vast data banks by the
computers. When man needs a small item of information he will request it
from the computers. The machines, to satisfy his need, will sometimes carry
on a simple dialogue with him until he obtains the data he wants. With
the early computers, a manager would often have dumped on his desk an indigestible
printout -- sometimes several hundred pages long. Now the manager is more
likely to request information when he needs it, and receive data about
a single item or situation on a screen or small printer. It is as though
man were surviving in the depths of this sea of information in a bathyscaphe.
Life in the bathyscaphe is simple, protected as it is from the pressure
of the vast quantities of data. Every now and then man peers through the
windows of the bathyscaphe to obtain facts that are necessary for some
purpose or other. The facts that he obtains at any one time are no more
than his animal brain can handle. The information windows must be designed
so that man, with his limited capabilities, can locate the data he wants
and obtain simple answers to questions that may need complex processing.
Some experts understand this distinction
clearly, such as Hannemyr and Innocent (1985) who write about "transforming
. . . data into information". But many system designers and users still
fail to recognize the difference.
Once a designer has determined what data
must be displayed, through analysis of user information requirements, the
next step is to decide how those data might best be formatted. Data might
be displayed as text, or in data forms, tables and/or various graphic formats.
Each of those types of data display is considered separately in the guidelines
presented here.
In some applications, the nature of the
data will dictate the necessary format, as in the graphic situation displays
used for air traffic control. In some applications, equipment limitations
may constrain display formatting, as in systems without graphic capability.
In many applications, however, a designer will have considerable latitude
in choosing how to display data. Good judgment may be needed to decide
when pictures or diagrams should be displayed rather than narrative text,
or vice versa.
In the subsections of guidelines dealing
with text, or data forms, or tables, or the various types of graphic displays,
the initial guidelines describe generally the circumstances in which that
particular type of data display may be appropriate. The design decision
will require careful analysis of the users' information handling tasks
to determine just what circumstances will actually prevail.
For data display, as in other areas
of user interface design, some general concepts deserve emphasis, including
the importance of context, consistency, and flexibility. Somehow a means
must be found to provide and maintain context in data displays so that
a user can find needed information. Task analysis may point the way here,
indicating what data are relevant to each step in task performance. Design
guidelines must emphasize the value of displaying no more data than the
user needs, and the importance of maintaining consistent display formats
so that the user always knows where to look for different kinds of information,
on any one display and from one display to another.
Detailed user information requirements
will vary, however, and may not be completely predictable in advance, even
with careful task analysis. Thus flexibility is needed so that a user can
tailor data displays on line to meet current needs. Such flexibility is
sometimes provided through optional data category selection and display
offset and expansion features. If options for tailoring display coverage
are provided, a user can adjust the assimilation of displayed data in a
way analogous to the self pacing of data entry.
When a user must both enter and retrieve data,
which is usually the case, the formatting of data displays should be consistent
with the methods used for data entry. As an example, if data entry is accomplished
via form filling, with specially formatted data fields, subsequent retrieval
of that data set should produce an output display with the same format,
especially if the user is expected to make changes to the displayed data
or additional entries. Where compaction of data output is required for
greater efficiency, perhaps to review multiple data sets in a single display
frame, the displayed items should retain at least the same ordering and
labeling as when those fields were used for data entry.
Display design must also take into account
the type of dialogue used for sequence control, and with hardware capabilities.
Where user inputs are made via menu selection, using a pointing device
like a lightpen, then display formats should give prominence (and adequate
separation) to the labeled, lightpennable options. Location of multifunction
keys at the display margin, to be labeled on the adjacent portion of the
display itself, may provide flexibility for both data entry and sequence
control, but will necessarily constrain display formatting.
These general concepts underlie many of
the guidelines for data display proposed in the following pages. As for
the other areas of user interface design, an attempt has been made to write
guidelines for data display in functional terms, insofar as possible without
reference to specific display devices and questions of hardware implementation.
As a practical matter, however, available display technology will inevitably
influence the wording of guidelines.
A discerning reader will note that the guidelines
presented here deal almost exclusively with visual displays; there are
only a few references to other possible display modes. Moreover, most of
these guidelines implicitly assume a fairly large visual display, with
room to show different kinds of data at one time -- in effect, a display
with about 24 lines of 80 characters, much like the devices we now use.
Consequently, many of these guidelines will not apply in applications where
displays are constrained to a smaller size, such as "briefcase" terminals
or handheld display devices.
As display technology develops further,
it seems inevitable that some of the guidelines proposed here must be reconsidered,
and other guidelines added. As an example, we may anticipate increased
use of graphics in future information display design, with moving (and
talking) pictures such as those we now enjoy in displays designed for entertainment.
The guidelines proposed here are
intended for display designers. If we regard displays as contrived arrangements
of data, then the guidelines refer to that contrivance. What happens in
applications where the computer provides a flexible capability allowing
users to contrive many of their own displays? If a user composes a poor
page of text, with long sentences, flawed grammar, inconsistent spacing,
etc., can a software designer be held responsible? Presumably not, or at
least not today.
One might imagine future systems, however,
where some form of expertise is stored in the computer, including expertise
on user interface design. In applications where users design their own
displays, a computer might someday suggest pertinent guidelines, or perhaps
even enforce design rules where warranted. For example, if a user entered
irregularly spaced text, a smart computer might regularize the spacing
in subsequent output of that text.
The guidelines presented here can themselves
be regarded as a long multipage data display. Problems of display organization
arise in presenting the guidelines material, in terms of content, wording,
and format. As in other sections, the topical organization of these guidelines
is based on function, dealing with different types of displayed data and
display manipulation. As in other sections, the guidelines here recommend
specific ways to accomplish some very general objectives.
Objectives Consistency of data display Efficient information
assimilation by the user Minimal memory load on user Compatibility of data
display with data entry Flexibility for user control of data display.
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