v Characteristics of a
user interface:
It is
very important to identify the characteristics desired of a good user
interface. Because unless we are aware of these, it is very much difficult to
design a good user interface. A few important characteristics of a good user
interface are the following:
1.
Speed of learning:
A good
user interface should be easy to learn. Speed of learning is hampered by
complex syntax and semantics of the command issue procedures. A good user
interface should not require its users to memorize commands. Neither should the
user be asked to remember information from one screen to another while
performing various tasks using the interface. Besides, the following three
issues are crucial to enhance the speed of learning:
Use of Metaphors and intuitive
command names:
Speed of learning
an interface is greatly facilitated if these are based on some day-to-day
real-life examples or some physical objects with which the users are familiar.
The abstractions of real-life objects or concepts used in user interface design
are called metaphors. If the user interface of a text editor uses concepts
similar to the tools used by a writer for text editing such as cutting lines
and paragraphs and pasting it at other places, users can immediately relate to
it. Another popular metaphor is a shopping cart. Everyone knows how a shopping
cart is used to make choices while purchasing items in a supermarket. If a user
interface uses the shopping cart metaphor for designing the interaction style
for a situation where similar types of choices have to be made, then the users
can easily understand and learn to use the interface. Yet another example of a
metaphor is the trashcan. To delete a file, the user may drag it to the
trashcan. Also, learning is facilitated by intuitive command names and symbolic
command issue procedures.
Consistency:
Once a
user learns about a command, he should be able to use the similar commands in
different circumstances for carrying out similar actions. This makes it easier
to learn the interface since
the user can extend his knowledge about one part of the
interface to the other parts. For example, in a word processor, “Control-b” is the short-cut key to embolden the
selected text. The same short-cut should be
used on the other parts of the interface, for example,
to embolden text in graphic objects also - circle, rectangle, polygon, etc. Thus, the different commands
supported by an interface should be
consistent.
Component-based
interface:
Users can learn an
interface faster if the interaction style of the interface is very similar to
the interface of other applications with which the user is already familiar.
This can be achieved if the interfaces of different applications are developed using
some standard user interface components. This, in fact, is the theme of the
component-based user interface. Examples of standard user interface components
are: radio button, check box, text field, slider, progress bar, etc.
The speed of learning characteristic
of a user interface can be determined by measuring the training time and
practice that users require before they can effectively use the software.
2. Speed
of use:
Speed of use of a user interface is determined by the time and
user effort necessary to initiate and execute different commands. This characteristic
of the interface is sometimes referred to as productivity support of the
interface. It indicates how fast the users can perform their intended tasks.
The time and user effort necessary to initiate and execute different commands
should be minimal. This can be achieved through careful design of the
interface. For example, an interface that requires users to type in lengthy
commands or involves mouse movements to different areas of the screen that are
wide apart for issuing commands can slow down the operating speed of users. The
most frequently used commands should have the smallest length or be available
at the top of the menu to minimize the mouse movements necessary to issue commands.
3.
Speed of recall:
Once users learn how to use an interface, the speed with which
they can recall the command issue procedure should be maximized. This
characteristic is very important for intermittent users. Speed of recall is
improved if the interface is based on some metaphors, symbolic command issue
procedures, and intuitive command names.
4. Error
prevention:
A good
user interface should minimize the scope of committing errors while initiating
different commands. The error rate of an interface can be easily determined by
monitoring the errors committed by average users while using the interface.
This monitoring can be automated by instrumenting the user interface code with
monitoring code which can record the frequency and types of user error and
later display the statistics of various kinds of errors committed by different
users.
Moreover,
errors can be prevented by asking the users to confirm any potentially
destructive actions specified by them, for example, deleting a group of files.
Consistency
of names, issue procedures, and behaviour of similar commands and the
simplicity of the command issue procedures minimize error possibilities. Also,
the interface should prevent the user from entering wrong values.
5.
Attractiveness:
A good user interface should be attractive to use. An attractive
user interface catches user attention and fancy. In this respect, graphics-based
user interfaces have a definite advantage over text-based interfaces.
6.
Consistency:
The commands supported by a user interface should be consistent.
The basic purpose of consistency is to allow users to generalize the knowledge
about aspects of the interface from one part to another. Thus, consistency
facilitates speed of learning, speed of recall, and also helps in reduction of
error rate.
7. Feedback:
A good user interface must provide feedback to various user actions.
Especially, if any user request takes more than few seconds to process, the
user should be informed about the state of the processing of his request. In
the absence of any response from the computer for a long time, a novice user
might even start recovery/shutdown procedures in panic. If required, the user
should be periodically informed about the progress made in processing his
command.
For example, if the user specifies a file copy/file download
operation, a progress bar can be displayed to display the status. This will
help the user to monitor the status of the action initiated.
8.
Support
for multiple skill levels:
A good user interface should support multiple levels of
sophistication of command issue procedure for different categories of users.
This is necessary because users with different levels of experience in using an
application prefer different types of user interfaces. Experienced users are
more concerned about the efficiency of the command issue procedure, whereas
novice users pay importance to usability aspects. Very cryptic and complex
commands discourage a novice, whereas elaborate command sequences make the
command issue procedure very slow and therefore put off experienced users. When
someone uses an application for the first time, his primary concern is speed of
learning. After using an application for extended periods of time, he becomes
familiar with the operation of the software. As a user becomes more and more
familiar with an interface, his focus shifts from usability aspects to speed of
command issue aspects. Experienced users look for options such as “hot-keys”,
“macros”, etc. Thus, the skill level of users improves as they keep using a
software product and they look for commands to suit their skill levels.
9. Error recovery (undo facility):
While issuing commands, even the expert users can commit errors.
Therefore, a good user interface should allow a user to undo a mistake
committed by him while using the interface. Users are put to inconvenience, if
they cannot recover from the errors they commit while using the software.
10. User guidance and on-line help:
Users
seek guidance and on-line help when they either forget a command or are unaware
of some features of the software. Whenever users need guidance or seek help
from the system, they should be provided with the appropriate guidance and
help.
v User guidance and online help
Users may
seek help about the operation of the software any time while using the software.
This is provided by the on-line help system. This is different from the
guidance and error messages which are flashed automatically without the user
asking for them. The guidance messages prompt the user regarding the options he
has regarding the next command, and the status of the last command, etc.
On-line Help System:
Users
expect the on-line help messages to be tailored to the context in which they
invoke the “help system”. Therefore, a good on-line help system should keep
track of what a user is doing while invoking the help system and provide the
output message in a context dependent way. Also, the help messages should be
tailored to the user’s experience level. Further, a good on-line help system
should take advantage of any graphics and animation characteristics of the
screen and should not just be a copy of the user’s manual. Fig. 9.1 gives a
snapshot of a typical on-line helps provided by a user interface.
Fig. 9.1. Example of an on-line help
interface
Guidance Messages:
The
guidance messages should be carefully designed to prompt the user about the
next actions he might purse, the current status of the system, the progress
made so far in processing his last command, etc. A good guidance system should have
different levels of sophistication for different categories of users. For
example, a user using a command language interface might need a different type
of guidance compared to a user using a menu or iconic interface. Also, users
should have an option to turn off detailed messages.
v Mode-based interface vs. modeless interface:
A mode is a state or collection
of states in which only a subset of all user interaction tasks can be
performed. In a modeless interface, the same set of commands can be invoked at
any time during the running of the software. Thus, a modeless interface has
only a single mode and all the commands are available all the time during the
operation of the software. On the other hand, in a mode-based interface,
different set of commands can be invoked depending on the mode in which the
system is, i.e. the mode at any instant is determined by the sequence of
commands already issued by the user.
A mode-based interface can
be represented using a state transition diagram, where each node of the state
transition diagram would represent a mode. Each state of the state transition
diagram can be annotated with the commands that are meaningful in that state.
Fig 9.2. An example of mode-based interface
Fig 9.2 shows the interface of a word processing program. The top-level
menu provides the user with a gamut of operations like file open, close, save,
etc. When the user chooses the open option, another frame is popped up which
limits the user to select a name from one of the folders.
v Graphical User Interface vs. Text-based User Interface
The following comparisons
are based on various characteristics of a GUI with those of a text-based user
interface.
In a GUI
multiple windows with different information can simultaneously be displayed on
the user screen. This is perhaps one of the biggest advantages of GUI over text
based interfaces since the user has the flexibility to simultaneously interact
with several related items at any time and can have access to different system
information displayed in different windows.
Iconic
information representation and symbolic information manipulation is possible in
a GUI. Symbolic information manipulation such as dragging an icon representing
a file to a trash can be deleting is intuitively very appealing and the user can
instantly remember it.
A GUI usually supports command
selection using an attractive and user-friendly menu selection system.
In a GUI,
a pointing device such as a mouse or a light pen can be used for issuing
commands. The use of a pointing device increases the efficacy issue procedure.
• On the
flip side, a GUI requires special terminals with graphics capabilities for
running and also requires special input devices such a mouse. On the other
hand, a text-based user interface can be implemented even on a cheap alphanumeric
display terminal. Graphics terminals are usually much more expensive than
alphanumeric terminals. However, display terminals with graphics capability
with bit-mapped high-resolution displays and significant amount of local
processing power have become affordable and over the years have replaced
text-based terminals on all desktops. Therefore, the emphasis of this lesson is
on GUI design rather than text based user interface design.
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