User interface design(sommerville) bangalore university

User Interface
Design

©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 1

User interface design Objectives
 Understand a number of user interface design principles
which have been introduced to serveral interaction styles
and understand when these are most appropriate.
 Understand when to user graphical and textual
persentation of information.

Know what is involved in the principal activities in the
user interface design process.

Understand usability attributes and have been introduced
to different approaches to interface evaluation.


UI design principles
User familiarity
• The interface should be based on user-oriented terms and concepts
rather than computer concepts
• E.g., an office system should use concepts such as letters, documents,
folders etc. rather than directories, file identifiers, etc.
Consistency
• The system should display an appropriate level of consistency
• Commands and menus should have the same format, command
punctuation should be similar, etc.
Minimal surprise
• If a command operates in a known way, the user should be able to
predict the operation of comparable commands


UI design principles (cont.)
Recoverability
• The system should provide some resilience to user errors and allow
the user to recover from errors
• This might include an undo facility, confirmation of destructive
actions, 'soft' deletes, etc.
User guidance
• Some user guidance such as help systems, on-line manuals, etc.
should be supplied
User diversity
• Interaction facilities for different types of user should be supported
• E.g., some users have seeing difficulties and so larger text should
be available


Topics Covered
 Design Issues
 The UI Design Process

User Analysis

User Interface Prototyping
 Interface Evaluation


Design Issues
The designer of a user interface to a computer is
faced with two key questions:
1. How should the user interact with the computer system?
2. How should information from the computer system be
presented to the user?


Interaction styles
Direct manipulation
• Easiest to grasp with immediate feedback
• Difficult to program
Menu selection
• User effort and errors minimized
• Large numbers and combinations of choices a problem
Form fill-in
• Ease of use, simple data entry
• Tedious, takes a lot of screen space
Command language
• Easy to program and process
• Difficult to master for casual users
Natural language
• Great for casual users
• Tedious for expert users


Information presentation
Information presentation is concerned with
presenting system information to system users
The information may be presented directly or may be
transformed in some way for presentation
The Model-View-Controller approach is a way of
supporting multiple presentations of data

Information to Presentation
be displayed software

Display

Information display factors
Is the user interested in precise information or
data relationships?
How quickly do information values change?
Must the change be indicated immediately?
Must the user take some action in response to a
change?
Is there a direct manipulation interface?
Is the information textual or numeric? Are
relative values important?


Alternative information presentations
Jan Feb M ar A il M
pr ay June
2842 2851 3164 2789 1273 2835

4000

3000

2000

1000

0
Jan Feb Mar A il M
pr ay June

Information display

1
0 10 20
4 2

3

Dial with needle Pie chart Thermometer Horizontal bar


Displaying relative values

Pressure Temper atu re
0 100 200 300 400 0 25 50 75 100


Design factors in message wording
 Context
 Experience

Skill Level
 Style
 Culture


Design factors in message wording
Context
Whenever possible, the messages generated
by the system should reflect the current user
context. As far as is possible, the system should
be aware of what the user is doing and should
generate messages that are relevant to their
current activity.


Design factors in message wording(Cntd.)

Experience
As users become familiar with a system they
become irritated by long. ‘Meaningfull’
messages. However, beginners find it difficult to
understand short, terse statements of a problem.
You should provide both types of messages and
allow the user to control message conciseness.



Skill Level
Messages should be tailored to the users’ skills
as well as their expericence. Messages for the
different classses of users may be expessed in
different ways depending on the terminology that
is familiar to the reader.



Style
Messages should be positive rather than
negative. They should use the active rather than
the passive mode of address. They should never
be insulting or try to be funny.



Culture
Whenever possible, the designer of messages
should be familiar with the culture of the contury
where the system is sold. There are distinct
differences between Europe, Asia and America. A
suitable message for one culture might be
unacceptable in another.


System and user-oriented error messages

U se r- o rie nte d e rro r me ssa g e
Sy ste m- o rie nte d e rro r me ssa g e

Erro r #27

?
Pa tie nt J. Ba te s is no t re g iste re d
Invalid patient id entered Click on Patients for a list of registered patients
Click on R etry to re-input a patient name
Click on Help for more information

OK C a nce l
Pa ti e nts H e lp R e tr
y C a nce l


User interface design process

Analyse and Produce paper- Evaluate design
understand user based design with end-users
activities prototype

Produce
Design Evaluate design
dynamic design
prototype with end-users
prototype

Executable Implement
prototype final user
interface


User Analysis
If you don’t understand what users want to do with
a system, then you have no realistic prospect of
designing an effective user interface. To develop
this understanding, you may user techniques such as
task analysis, ethnographic studies, user
interviews and observations or commonly, a
mixture of all of these.


Analysis Techniques
Hierarchical Task Analysis(HTA)
In HTA, a high level task is broken down into
subtasks, and plans are identified that specify
what might happen in a specific suitation.


Analysis Techniques (Cntd.)
Ethnography
It closely observe how people work, how
they interact with others and how features in the
workplace are used to support their work. The
advantage of ethnography is that the ethnographer
can observe intuitive actions and informal
collabrations that can then spark further
discussions about the work.


User Interface Prototyping
Approachers
 Paper Prototyping

Storyboard
3 Main Approachers
 Script-driven approach(Macromedia)
 Visual Programming Languages(VB)
 Internet-Based Prototyping(Java)


Interface Evaluation
It is the process of assessing the usability of
an interface and checking that it meets user
requirements. Therefore, it should be part of the
normal verification and validation process for
software system.


Simple evaluation techniques
Questionnaires for user feedback
Video recording of system use and subsequent
tape evaluation.
Instrumentation of code to collect information
about facility use and user errors.
The provision of a “gripe” button for on-line user
feedback.


Usability attributes
Attribute Description
Learnability How long does it take a new user to
become productive with the system?
Speed of operation How well does the system response match
the user’s work practice?
Robustness How tolerant is the system of user error?
Recoverability How good is the system at recovering from
user errors?
Adaptability How closely is the system tied to a single
model of work?


Key points
Interface design should be user-centred. An
interface should be logical and consistent and
help users recover from errors
Interaction styles include direct manipulation,
menu systems form fill-in, command languages,
and natural language
Graphical displays should be used to present
trends and approximate values. Digital displays
when precision is required
Colour should be used sparingly and consistently

Key points
Ideally, a user interface should be evaluated
against a usability specification
What about help for the user?
• Systems should provide on-line help. This should include “help,
I’m in trouble” and “help, I want information”
• A range of different types of user documents should be
provided


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