Bài giảng Introduction to Software Engineering - Week 8: UI Design - Nguyễn Thị Minh Tuyền

short-term memory
 p People can instantaneously remember about 7 items of information.
 If you present more than this, they are more liable to make
 mistakes.
£ People make mistakes
 p When people make mistakes and systems go wrong, inappropriate
 alarms and messages can increase stress and hence the likelihood
 of more mistakes.
£ People are different
 p People have a wide range of physical capabilities. Designers should
 not just design for their own capabilities.
£ People have different interaction preferences
 p Some like pictures, some like text.
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 UI design principles
£ UI design must take account of the needs,
 experience and capabilities of the system users.
£ Designers should
 p be aware of peoples physical and mental limitations
 (e.g. limited short-term memory) and
 p should recognise that people make mistakes.
£ UI design principles underlie interface designs
 although not all principles are applicable to all
 designs.
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 UI design principles
£ User familiarity
 p The interface should use terms and concepts which are
 drawn from the experience of the people who will make
 most use of the system.
£ Consistency
 p The interface should be consistent in that, wherever
 possible, comparable operations should be activated in
 the same way.
£ Minimal surprise
 p Users should never be surprised by the behaviour of a
 system.
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 UI design principles
£ Recoverability
 p The interface should include mechanisms to allow users
 to recover from errors.
£ User guidance
 p The interface should provide meaningful feedback when
 errors occur and provide context-sensitive user help
 facilities.
£ User diversity
 p The interface should provide appropriate interaction
 facilities for different types of system user.
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 Design issues in UIs
£ Two problems must be addressed in interactive
 systems design
 p How should the user interact with the computer
 system?
 p How should information from the computer system be
 presented to the user?
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 Interaction styles
£ Direct manipulation
£ Menu selection
£ Form fill-in
£ Command language
£ Natural language
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 Interaction styles
Interaction Main advantages Main disadvantages Application 
style examples 
Direct Fast and intuitive May be hard to implement. Video games 
manipulation interaction Only suitable where there is a CAD systems 
 Easy to learn visual metaphor for tasks and 
 objects. 
Menu Avoids user error Slow for experienced users. Most general-
selection Little typing required Can become complex if many purpose systems 
 menu options. 
Form fill-in Simple data entry Takes up a lot of screen space. Stock control, 
 Easy to learn Causes problems where user Personal loan 
 Checkable options do not match the form processing 
 fields. 
Command Powerful and flexible Hard to learn. Operating systems, 
language Poor error management. Command and 
 control systems 
Natural Accessible to casual Requires more typing. Information 
language users Natural language understanding retrieval systems 
 Easily extended systems are unreliable. 
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Multiple user interfaces
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 Web-based interfaces
£ Many web-based systems have interfaces based
 on web forms.
£ Form field can be menus, free text input, radio
 buttons, etc.
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 Example: LIBSYS system
£ Users make a choice of where to search from a
 menu and type the search phrase into a free text
 field.
£ LIBSYS interaction
 p Document search: Users need to be able to use the
 search facilities to find the documents that they need.
 p Document request: Users request that a document be
 delivered to their machine or to a server for printing.
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LIBSYS search form
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 Information presentation
£ Is concerned with presenting system 
 information to system users.
£ The information may be
 p presented directly (e.g. text in a word processor)
 p or transformed in some way for presentation (e.g. in
 some graphical form).
£ The Model-View-Controller approach is a way of
 supporting multiple presentations of data.
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Information presentation
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MVC model of user interaction
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 Information presentation
£ Static information
 p Initialised at the beginning of a session. It does not
 change during the session.
 p May be either numeric or textual.
£ Dynamic information
 p Changes during a session and the changes must be
 communicated to the system user.
 p May be either numeric or textual.
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 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?
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 Alternative information presentations
• Digital presentation
 • Compact - takes up little screen 
 space;
 • Precise values can be 
 communicated.
• Analogue presentation
 • Easier to get an 'at a glance' 
 impression of a value;
 • Possible to show relative 
 values;
 • Easier to see exceptional data 
 values.
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Presentation methods
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Displaying relative values
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 Data visualisation
£ Concerned with techniques for displaying large
 amounts of information.
£ Visualisation can reveal relationships between
 entities and trends in the data.
£ Possible data visualisations are:
 p Weather information collected from a number of
 sources;
 p The state of a telephone network as a linked set of
 nodes;
 p Chemical plant visualised by showing pressures and
 temperatures in a linked set of tanks and pipes;
 p A model of a molecule displayed in 3 dimensions.
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 Colour displays
£ Colour adds an extra dimension to an interface
 and can help the user understand complex
 information structures.
£ Colour can be used to highlight exceptional
 events.
£ Common mistakes in the use of colour in
 interface design include:
 p The use of colour to communicate meaning;
 p The over-use of colour in the display.
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Example
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 Colour use guidelines
£ Limit the number of colours used and be
 conservative in their use.
£ Use colour change to show a change in system
 status.
£ Use colour coding to support the task that users
 are trying to perform.
£ Use colour coding in a thoughtful and consistent
 way.
£ Be careful about colour pairings.
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 Error messages
£ Error message design is critically important.
 p Poor error messages can mean that a user
 rejects rather than accepts a system.
£ Messages should be polite, concise, consistent
 and constructive.
£ The background and experience of users
 should be the determining factor in message
 design.
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 Design factors in message wording
Factor Description
Context Wherever 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.
Experience As u sers become familiar with a s ystem they become irritated by long, ‘meaningful’
 messages. However, beginners find it difficult to understand short terse statements of a
 problem. You should provide both types of message and allow the user to control
 message conciseness.
Skill level Messages should be tailored to the user’s skills as well as their experience. Messages
 for the different classes of user may be ex pressed in d ifferent 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 Wherever possible, the designer of messages should be familiar with the culture of the
 country where the system is sold. There are distinct cultural differences between
 Europe, Asia and America. A suitable message for one culture might be unacceptable
 in another. 29
 User error
£ Assume that a nurse misspells the name of a
 patient whose records he is trying to retrieve.
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Good and bad message design
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 Topics covered
1. Design issues
2. User interface design process
3. User analysis
4. User interface prototyping
5. Interface evaluation
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 UI design process
£ UI design is an iterative process involving close
 liaisons between users and designers.
£ The 3 core activities in this process are:
 p User analysis. Understand what the users will do with
 the system;
 p System prototyping. Develop a series of prototypes for
 experiment;
 p Interface evaluation. Experiment with these prototypes
 with users.
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The design process
 34
 Topics covered
1. Design issues
2. User interface design process
3. User analysis
4. User interface prototyping
5. Interface evaluation
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 User analysis
£ If you don’t understand what the users want to do
 with a system, you have no realistic prospect of
 designing an effective interface.
£ User analyses have to be described in terms that
 users and other designers can understand.
£ Scenarios where you describe typical episodes of
 use, are one way of describing these analyses.
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 User interaction scenario
Jane is a student of Religious Studies and is working on an essay
on Indian architecture and how it has been influenced by
religious practices. To help her understand this, she would like to
access some pictures of details on notable buildings but can’t
find anything in her local library.
She approaches the subject librarian to discuss her needs and he
suggests some search terms that might be used. He also suggests
some libraries in New Delhi and London that might have this
material so they log on to the library catalogues and do some
searching using these terms. They find some source material and
place a request for photocopies of the pictures with architectural
detail to be posted directly to Jane.
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 Requirements from the scenario
£ Users may not be aware of appropriate search
 terms so need a way of helping them choose
 terms.
£ Users have to be able to select collections to
 search.
£ Users need to be able to carry out searches and
 request copies of relevant material.
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 Analysis techniques
£ Task analysis
 p Models the steps involved in completing a task.
£ Interviewing and questionnaires
 p Asks the users about the work they do.
£ Ethnography
 p Observes the user at work.
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Hierarchical task analysis (HTA)
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 Interviewing
£ Design semi-structured interviews based on open-
 ended questions.
£ Users can then provide information that they think
 is essential; not just information that you have
 thought of collecting.
£ Group interviews or focus groups allow users to
 discuss with each other what they do.
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 Ethnography
£ Involves an external observer watching users at
 work and questioning them in an unscripted way
 about their work.
£ Valuable because many user tasks are intuitive
 and they find these very difficult to describe and
 explain.
£ Also helps understand the role of social and
 organisational influences on work.
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 Ethnographic records
Air traffic control involves a number of control ‘suites’ where the
suites controlling adjacent sectors of airspace are physically
located next to each other. Flights in a sector are represented by
paper strips that are fitted into wooden racks in an order that
reflects their position in the sector. If there are not enough slots
in the rack (i.e. when the airspace is very busy), controllers
spread the strips out on the desk in front of the rack.
When we were observing controllers, we noticed that controllers
regularly glanced at the strip racks in the adjacent sector. We
pointed this out to them and asked them why they did this. They
replied that, if the adjacent controller has strips on their desk,
then this meant that they would have a lot of flights entering their
sector. They therefore tried to increase the speed of aircraft in
the sector to ‘clear space’ for the incoming aircraft.
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 Insights from ethnography
£ Controllers had to see all flights in a sector.
 Therefore, scrolling displays where flights
 disappeared off the top or bottom of the display
 should be avoided.
£ The interface had to have some way of telling
 controllers how many flights were in adjacent
 sectors so that they could plan their workload.
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 Topics covered
1. Design issues
2. User interface design process
3. User analysis
4. User interface prototyping
5. Interface evaluation
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 User interface prototyping
£ The aim of prototyping is to allow users to gain
 direct experience with the interface.
£ Without such direct experience, it is impossible to
 judge the usability of an interface.
£ Prototyping may be a two-stage process:
 p Early in the process, paper prototypes may be used;
 p The design is then refined and increasingly
 sophisticated automated prototypes are then developed.
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 Paper prototyping
£ Work through scenarios using sketches of the
 interface.
£ Use a storyboard to present a series of
 interactions with the system.
£ Paper prototyping is an effective way of getting
 user reactions to a design proposal.
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 Prototyping techniques
£ Script-driven prototyping
 p Develop a set of scripts and screens using a tool such
 as Macromedia Director. When the user interacts with
 these, the screen changes to the next display.
£ Visual programming
 p Use a language designed for rapid development such as
 Visual Basic.
£ Internet-based prototyping
 p Use a web browser and associated scripts.
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 Topics covered
1. Design issues
2. User interface design process
3. User analysis
4. User interface prototyping
5. Interface evaluation
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 User interface evaluation
£ Some evaluation of a user interface design
 should be carried out to assess its suitability.
£ Full scale evaluation is very expensive and
 impractical for most systems.
£ Ideally, an interface should be evaluated against a
 usability specification. However, it is rare for such
 specifications to be produced.
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 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? 
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 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 code in the software to collect
 on-line user feedback.
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