Ch15
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User interface design ●
Designing effective interfaces for software systems
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 1
Objectives ●
● ● ●
●
To suggest some general design principles for user interface design To explain different interaction styles To introduce styles of information presentation To describe the user support which should be builtin to user interfaces To introduce usability attributes and system approaches to system evaluation
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 2
Topics covered ● ● ● ● ●
User interface design principles User interaction Information presentation User support Interface evaluation
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 3
The user interface ●
●
●
System users often judge a system by its interface rather than its functionality A poorly designed interface can cause a user to make catastrophic errors Poor user interface design is the reason why so many software systems are never used
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 4
Graphical user interfaces ●
Most users of business systems interact with these systems through graphical interfaces although, in some cases, legacy textbased interfaces are still used
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 5
GUI characteristics Characteristic Windows Icons Menus Pointing Graphics
©Ian Sommerville 2000
Description Multiple windows allow different information to be displayed simultaneously on the userÕs screen. Icons different types of information. On some systems, icons represent files; on others, icons represent processes. Commands are selected from a menu rather than typed in a command language. A pointing device such as a mouse is used for selecting choices from a menu or indicating items of interest in a window. Graphical elements can be mixed with text on the same display.
Software Engineering, 6th edition. Chapter 15
Slide 6
GUI advantages ●
They are easy to learn and use. •
●
The user may switch quickly from one task to another and can interact with several different applications. •
●
Users without experience can learn to use the system quickly.
Information remains visible in its own window when attention is switched.
Fast, fullscreen interaction is possible with immediate access to anywhere on the screen
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 7
Usercentred design ●
●
●
The aim of this chapter is to sensitise software engineers to key issues underlying the design rather than the implementation of user interfaces Usercentred design is an approach to UI design where the needs of the user are paramount and where the user is involved in the design process UI design always involves the development of prototype interfaces
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 8
ludecriytvse an A n a d P r o d u c e p a e r aw v lihutneP d srouduiegrcn userbapsD ietsoigyngnE d s e E v a l u t e d s i g n d y n a m i s i g n w i h n u e r protype E tpxreocutyy p p lfintaer fm p tuscer n ab lpe Im
User interface design process
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 9
UI design principles ●
●
●
UI design must take account of the needs, experience and capabilities of the system users Designers should be aware of people’s physical and mental limitations (e.g. limited shortterm memory) and should recognise that people make mistakes UI design principles underlie interface designs although not all principles are applicable to all designs
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 10
User interface design principles Principle User familiarity Consistency Minimal surprise Recoverability User guidance User diversity
©Ian Sommerville 2000
Description The interface should use terms and concepts which are drawn from the experience of the people who will make most use of the system. The interface should be consistent in that, wherever possible, comparable operations should be activated in the same way. Users should never be surprised by the behaviour of a system. The interface should include mechanisms to allow users to recover from errors. The interface should provide meaningful feedback when errors occur and provide contextsensitive user help facilities. The interface should provide appropriate interaction facilities for different types of system user.
Software Engineering, 6th edition. Chapter 15
Slide 11
Design principles ●
User familiarity •
●
Consistency •
●
The interface should be based on useroriented terms and concepts rather than computer concepts. For example, an office system should use concepts such as letters, documents, folders etc. rather than directories, file identifiers, etc. 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 •
©Ian Sommerville 2000
If a command operates in a known way, the user should be able to predict the operation of comparable commands Software Engineering, 6th edition. Chapter 15
Slide 12
Design principles ●
Recoverability •
●
User guidance •
●
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. Some user guidance such as help systems, online manuals, etc. should be supplied
User diversity •
©Ian Sommerville 2000
Interaction facilities for different types of user should be supported. For example, some users have seeing difficulties and so larger text should be available Software Engineering, 6th edition. Chapter 15
Slide 13
Usersystem interaction ●
Two problems must be addressed in interactive systems design • •
●
How should information from the user be provided to the computer system? How should information from the computer system be presented to the user?
User interaction and information presentation may be integrated through a coherent framework such as a user interface metaphor
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 14
Interaction styles ● ● ● ● ●
Direct manipulation Menu selection Form fillin Command language Natural language
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 15
Interaction style Direct manipulatio n
Main advantages Fast and intuitive interaction Easy to learn
Menu selection
Avoids user error Little typing required
Form fillin
Simple data entry Easy to learn Powerful and flexible
Command language Natural language
Accessible to casual users Easily extended
Main disadvantages May be hard to implement Only suitable where there is a visual metaphor for tasks and objects Slow for experienced users Can become complex if many menu options Takes up a lot of screen space Hard to learn Poor error management Requires more typing Natural language understanding systems are unreliable
Application examples Video games CAD systems
Most general purpose systems
Stock control, Personal loan processing Operating systems, Library information retrieval systems Timetable systems WWW information retrieval systems
Advantages and disadvantages
Direct manipulation advantages ●
● ●
Users feel in control of the computer and are less likely to be intimidated by it User learning time is relatively short Users get immediate feedback on their actions so mistakes can be quickly detected and corrected
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 17
Direct manipulation problems ●
●
●
The derivation of an appropriate information space model can be very difficult Given that users have a large information space, what facilities for navigating around that space should be provided? Direct manipulation interfaces can be complex to program and make heavy demands on the computer system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 18
G r i d B u s y tT iM T lypeh J S D . e x a m p l e o d O U I T e N e t w o r k U n i t s c m S lN cO tD ioE nP rL cIN sK R e d u c e F u l P R I N T SF O N TL A B E LE D IT
Control panel interface
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 19
Menu systems ●
●
●
Users make a selection from a list of possibilities presented to them by the system The selection may be made by pointing and clicking with a mouse, using cursor keys or by typing the name of the selection May make use of simpletouse terminals such as touchscreens
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 20
Advantages of menu systems ●
● ● ●
Users need not remember command names as they are always presented with a list of valid commands Typing effort is minimal User errors are trapped by the interface Contextdependent help can be provided. The user’s context is indicated by the current menu selection
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 21
Problems with menu systems ●
●
●
Actions which involve logical conjunction (and) or disjunction (or) are awkward to represent Menu systems are best suited to presenting a small number of choices. If there are many choices, some menu structuring facility must be used Experienced users find menus slower than command language
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 22
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Formbased interface
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 23
Command interfaces ●
● ● ●
●
User types commands to give instructions to the system e.g. UNIX May be implemented using cheap terminals. Easy to process using compiler techniques Commands of arbitrary complexity can be created by command combination Concise interfaces requiring minimal typing can be created
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 24
Problems with command interfaces ●
●
●
Users have to learn and remember a command language. Command interfaces are therefore unsuitable for occasional users Users make errors in command. An error detection and recovery system is required System interaction is through a keyboard so typing ability is required
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 25
Command languages ●
● ●
Often preferred by experienced users because they allow for faster interaction with the system Not suitable for casual or inexperienced users May be provided as an alternative to menu commands (keyboard shortcuts). In some cases, a command language interface and a menubased interface are supported at the same time
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 26
Natural language interfaces ●
●
The user types a command in a natural language. Generally, the vocabulary is limited and these systems are confined to specific application domains (e.g. timetable enquiries) NL processing technology is now good enough to make these interfaces effective for casual users but experienced users find that they require too much typing
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 27
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Multiple user interfaces
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 28
Information presentation ●
●
●
Information presentation is concerned with presenting system information to system users The information may be presented directly (e.g. text in a word processor) or may be transformed in some way for presentation (e.g. in some graphical form) The ModelViewController approach is a way of supporting multiple presentations of data
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 29
In fbeo drm tisplioyne dtoP a reosfnw tarieon D isplay
Information presentation
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 30
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Modelviewcontroller
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 31
Information presentation ●
Static information • •
●
Initialised at the beginning of a session. It does not change during the session May be either numeric or textual
Dynamic information • •
©Ian Sommerville 2000
Changes during a session and the changes must be communicated to the system user May be either numeric or textual
Software Engineering, 6th edition. Chapter 15
Slide 32
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?
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 33
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Alternative information presentations
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 34
Analogue vs. digital presentation ●
Digital presentation • •
●
Compact takes up little screen space Precise values can be communicated
Analogue presentation • • •
©Ian Sommerville 2000
Easier to get an 'at a glance' impression of a value Possible to show relative values Easier to see exceptional data values
Software Engineering, 6th edition. Chapter 15
Slide 35
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Dynamic information display
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 36
P r e s u r e T e m p e r a t u r e 010203040025507510
Displaying relative values
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 37
T h e f i l e n a m e y o u h a v e c h o s e n h a s b e n u s d . P s c h s n t r m !C h. 16U sO eK r interface d sC ian gcnel
Textual highlighting
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 38
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: • • • • •
©Ian Sommerville 2000
Weather information collected from a number of sources The state of a telephone network as a linked set of nodes Chemical plant visualised by showing pressures and temperatures in a linked set of tanks and pipes A model of a molecule displayed in 3 dimensions Web pages displayed as a hyperbolic tree Software Engineering, 6th edition. Chapter 15
Slide 39
Colour displays ●
● ●
Colour adds an extra dimension to an interface and can help the user understand complex information structures Can be used to highlight exceptional events Common mistakes in the use of colour in interface design include: • •
©Ian Sommerville 2000
The use of colour to communicate meaning Overuse of colour in the display
Software Engineering, 6th edition. Chapter 15
Slide 40
Colour use guidelines ● ● ● ● ● ● ● ●
Don't use too many colours Use colour coding to support use tasks Allow users to control colour coding Design for monochrome then add colour Use colour coding consistently Avoid colour pairings which clash Use colour change to show status change Be aware that colour displays are usually lower resolution
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 41
User support ●
●
●
User guidance covers all system facilities to support users including online help, error messages, manuals etc. The user guidance system should be integrated with the user interface to help users when they need information about the system or when they make some kind of error The help and message system should, if possible, be integrated
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 42
A p l i c a t o n lintrfapceprM H e E r o m e s a g e s y t e s a g e n t i o n y m lfram H e ps E rot m exsage
Help and message system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 43
Error messages ●
●
●
Error message design is critically important. 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
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 44
Design factors in message wording Context Experience
Skill level
Style Culture
©Ian Sommerville 2000
The user guidance system should be aware of what the user is doing and should adjust the output message to the current context. As users become familiar with a system they become irritated by long, ÔmeaningfulÕ messages. However, beginners find it difficult to understand short terse statements of the problem. The user guidance system should provide both types of message and allow the user to control message conciseness. Messages should be tailored to the userÕs skills as well as their experience. Messages for the different classes of user may be expressed in different ways depending on the terminology which is familiar to the reader. 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. 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. Software Engineering, 6th edition. Chapter 15
Slide 45
Pleas x t lic k Bates , J .OK Can
Nurse input of a patient’s name
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 46
Use System Err or #2 P a . Ba tie Clic k on atie or In vaCanc lid pa ?OK y to or m P aHe tie Re yC System and useroriented error messages
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 47
Help system design ● ● ●
●
Help? means ‘help I want information” Help! means “HELP. I'm in trouble” Both of these requirements have to be taken into account in help system design Different facilities in the help system may be required
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 48
Help information ● ●
●
●
Should not simply be an online manual Screens or windows don't map well onto paper pages. The dynamic characteristics of the display can improve information presentation. People are not so good at reading screen as they are text.
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 49
Help system use ●
●
●
Multiple entry points should be provided so that the user can get into the help system from different places. Some indication of where the user is positioned in the help system is valuable. Facilities should be provided to allow the user to navigate and traverse the help system.
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 50
T enotprylevl taprlyic fartom E n n tm E n resya fgreom syetrm o H elp fram e ntw ork
Entry points to a help system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 51
H elp fram e m apM M a i l r e d i r e c t i o n n lrp in a m a y b e d a o t h e r e t w o r k u s r y p r e s i n g t h e d c t t o n i t h c o r l a l . T h e s e m a k f m e o f u r o u s e t o w h t m a i l h b n s e n Y o u a r e h r e m o r e n e x t t o p i c s 2 l1 H e p h i s t o r y 4. M .3 a eR S nidr em actioln
Help system windows
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 52
User documentation ●
●
●
As well as online information, paper documentation should be supplied with a system Documentation should be designed for a range of users from inexperienced to experienced As well as manuals, other easytouse documentation such as a quick reference card may be provided
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 53
teF S y s e m S y s t e m N o v i c e E x p e r i n c e d S y s t e m adeuslnucrtpio v ronsaladIm idnson rtcaulm ateioonrsIntm sroadnurcto u u s a d m i n r a o r s r y R e f r e n c A d m i n s t r a o r Õ s l m a u a l g u d e D escrivptco esfH n thestoyinesm o w talG esatrindgdeF ascrilptyonO rm p e antion aced User document types
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 54
Document types ●
Functional description •
●
Introductory manual •
●
Describes all system facilities in detail
System installation manual •
●
Presents an informal introduction to the system
System reference manual •
●
Brief description of what the system can do
Describes how to install the system
System administrator’s manual •
©Ian Sommerville 2000
Describes how to manage the system when it is in use Software Engineering, 6th edition. Chapter 15
Slide 55
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
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 56
Usability attributes Attribute Learnability Speed of operation Robustness Recoverability Adaptability
©Ian Sommerville 2000
Description How long does it take a new user to become productive with the system? How well does the system response match the userÕs work practice? How tolerant is the system of user error? How good is the system at recovering from user errors? How closely is the system tied to a single model of work?
Software Engineering, 6th edition. Chapter 15
Slide 57
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 grip button for online user feedback.
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 58
Key points ●
●
●
●
Interface design should be usercentred. An interface should be logical and consistent and help users recover from errors Interaction styles include direct manipulation, menu systems form fillin, 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
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 59
Key points ●
●
●
●
Systems should provide online help. This should include “help, I’m in trouble” and “help, I want information” Error messages should be positive rather than negative. A range of different types of user documents should be provided Ideally, a user interface should be evaluated against a usability specification
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 60
Designing effective interfaces for software systems
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 1
Objectives ●
● ● ●
●
To suggest some general design principles for user interface design To explain different interaction styles To introduce styles of information presentation To describe the user support which should be builtin to user interfaces To introduce usability attributes and system approaches to system evaluation
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 2
Topics covered ● ● ● ● ●
User interface design principles User interaction Information presentation User support Interface evaluation
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 3
The user interface ●
●
●
System users often judge a system by its interface rather than its functionality A poorly designed interface can cause a user to make catastrophic errors Poor user interface design is the reason why so many software systems are never used
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 4
Graphical user interfaces ●
Most users of business systems interact with these systems through graphical interfaces although, in some cases, legacy textbased interfaces are still used
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 5
GUI characteristics Characteristic Windows Icons Menus Pointing Graphics
©Ian Sommerville 2000
Description Multiple windows allow different information to be displayed simultaneously on the userÕs screen. Icons different types of information. On some systems, icons represent files; on others, icons represent processes. Commands are selected from a menu rather than typed in a command language. A pointing device such as a mouse is used for selecting choices from a menu or indicating items of interest in a window. Graphical elements can be mixed with text on the same display.
Software Engineering, 6th edition. Chapter 15
Slide 6
GUI advantages ●
They are easy to learn and use. •
●
The user may switch quickly from one task to another and can interact with several different applications. •
●
Users without experience can learn to use the system quickly.
Information remains visible in its own window when attention is switched.
Fast, fullscreen interaction is possible with immediate access to anywhere on the screen
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 7
Usercentred design ●
●
●
The aim of this chapter is to sensitise software engineers to key issues underlying the design rather than the implementation of user interfaces Usercentred design is an approach to UI design where the needs of the user are paramount and where the user is involved in the design process UI design always involves the development of prototype interfaces
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 8
ludecriytvse an A n a d P r o d u c e p a e r aw v lihutneP d srouduiegrcn userbapsD ietsoigyngnE d s e E v a l u t e d s i g n d y n a m i s i g n w i h n u e r protype E tpxreocutyy p p lfintaer fm p tuscer n ab lpe Im
User interface design process
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 9
UI design principles ●
●
●
UI design must take account of the needs, experience and capabilities of the system users Designers should be aware of people’s physical and mental limitations (e.g. limited shortterm memory) and should recognise that people make mistakes UI design principles underlie interface designs although not all principles are applicable to all designs
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 10
User interface design principles Principle User familiarity Consistency Minimal surprise Recoverability User guidance User diversity
©Ian Sommerville 2000
Description The interface should use terms and concepts which are drawn from the experience of the people who will make most use of the system. The interface should be consistent in that, wherever possible, comparable operations should be activated in the same way. Users should never be surprised by the behaviour of a system. The interface should include mechanisms to allow users to recover from errors. The interface should provide meaningful feedback when errors occur and provide contextsensitive user help facilities. The interface should provide appropriate interaction facilities for different types of system user.
Software Engineering, 6th edition. Chapter 15
Slide 11
Design principles ●
User familiarity •
●
Consistency •
●
The interface should be based on useroriented terms and concepts rather than computer concepts. For example, an office system should use concepts such as letters, documents, folders etc. rather than directories, file identifiers, etc. 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 •
©Ian Sommerville 2000
If a command operates in a known way, the user should be able to predict the operation of comparable commands Software Engineering, 6th edition. Chapter 15
Slide 12
Design principles ●
Recoverability •
●
User guidance •
●
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. Some user guidance such as help systems, online manuals, etc. should be supplied
User diversity •
©Ian Sommerville 2000
Interaction facilities for different types of user should be supported. For example, some users have seeing difficulties and so larger text should be available Software Engineering, 6th edition. Chapter 15
Slide 13
Usersystem interaction ●
Two problems must be addressed in interactive systems design • •
●
How should information from the user be provided to the computer system? How should information from the computer system be presented to the user?
User interaction and information presentation may be integrated through a coherent framework such as a user interface metaphor
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 14
Interaction styles ● ● ● ● ●
Direct manipulation Menu selection Form fillin Command language Natural language
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 15
Interaction style Direct manipulatio n
Main advantages Fast and intuitive interaction Easy to learn
Menu selection
Avoids user error Little typing required
Form fillin
Simple data entry Easy to learn Powerful and flexible
Command language Natural language
Accessible to casual users Easily extended
Main disadvantages May be hard to implement Only suitable where there is a visual metaphor for tasks and objects Slow for experienced users Can become complex if many menu options Takes up a lot of screen space Hard to learn Poor error management Requires more typing Natural language understanding systems are unreliable
Application examples Video games CAD systems
Most general purpose systems
Stock control, Personal loan processing Operating systems, Library information retrieval systems Timetable systems WWW information retrieval systems
Advantages and disadvantages
Direct manipulation advantages ●
● ●
Users feel in control of the computer and are less likely to be intimidated by it User learning time is relatively short Users get immediate feedback on their actions so mistakes can be quickly detected and corrected
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 17
Direct manipulation problems ●
●
●
The derivation of an appropriate information space model can be very difficult Given that users have a large information space, what facilities for navigating around that space should be provided? Direct manipulation interfaces can be complex to program and make heavy demands on the computer system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 18
G r i d B u s y tT iM T lypeh J S D . e x a m p l e o d O U I T e N e t w o r k U n i t s c m S lN cO tD ioE nP rL cIN sK R e d u c e F u l P R I N T SF O N TL A B E LE D IT
Control panel interface
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 19
Menu systems ●
●
●
Users make a selection from a list of possibilities presented to them by the system The selection may be made by pointing and clicking with a mouse, using cursor keys or by typing the name of the selection May make use of simpletouse terminals such as touchscreens
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 20
Advantages of menu systems ●
● ● ●
Users need not remember command names as they are always presented with a list of valid commands Typing effort is minimal User errors are trapped by the interface Contextdependent help can be provided. The user’s context is indicated by the current menu selection
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 21
Problems with menu systems ●
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Actions which involve logical conjunction (and) or disjunction (or) are awkward to represent Menu systems are best suited to presenting a small number of choices. If there are many choices, some menu structuring facility must be used Experienced users find menus slower than command language
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 22
N E W B O K tP iA T luubtehliosrher IP S B N r i c e u b l a t i o n d a t e N u m b r o f tD iC E d o n c o p i e s lpuartsce hoiafsceation L o a n tstradu sO sues
Formbased interface
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 23
Command interfaces ●
● ● ●
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User types commands to give instructions to the system e.g. UNIX May be implemented using cheap terminals. Easy to process using compiler techniques Commands of arbitrary complexity can be created by command combination Concise interfaces requiring minimal typing can be created
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 24
Problems with command interfaces ●
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●
Users have to learn and remember a command language. Command interfaces are therefore unsuitable for occasional users Users make errors in command. An error detection and recovery system is required System interaction is through a keyboard so typing ability is required
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 25
Command languages ●
● ●
Often preferred by experienced users because they allow for faster interaction with the system Not suitable for casual or inexperienced users May be provided as an alternative to menu commands (keyboard shortcuts). In some cases, a command language interface and a menubased interface are supported at the same time
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 26
Natural language interfaces ●
●
The user types a command in a natural language. Generally, the vocabulary is limited and these systems are confined to specific application domains (e.g. timetable enquiries) NL processing technology is now good enough to make these interfaces effective for casual users but experienced users find that they require too much typing
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 27
o m a n d G rap inG lteU h rfIuser C c a lC ailo n g u e t e r f c m a n d a n g u e m angerO i t e r p t r perating sytem
Multiple user interfaces
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 28
Information presentation ●
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Information presentation is concerned with presenting system information to system users The information may be presented directly (e.g. text in a word processor) or may be transformed in some way for presentation (e.g. in some graphical form) The ModelViewController approach is a way of supporting multiple presentations of data
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 29
In fbeo drm tisplioyne dtoP a reosfnw tarieon D isplay
Information presentation
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 30
V iV eiew w s m taeethodsview m o daifgecsationC ontrolerm staheodsU e s s e r i n p u t s M lan pqduaetris M o d e M o d e l d i t s M lodel m o d e settahoeds
Modelviewcontroller
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 31
Information presentation ●
Static information • •
●
Initialised at the beginning of a session. It does not change during the session May be either numeric or textual
Dynamic information • •
©Ian Sommerville 2000
Changes during a session and the changes must be communicated to the system user May be either numeric or textual
Software Engineering, 6th edition. Chapter 15
Slide 32
Information display factors ●
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●
● ●
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?
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 33
J a n F e b M a r A p r i l M a y J u n e 2 8 4 2 2 8 5 1 3 1 6 4 2 7 8 9 1 2 7 3 2 8 3 5 4 0 3200 100JanF ebM arA prilM ayJune
Alternative information presentations
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 34
Analogue vs. digital presentation ●
Digital presentation • •
●
Compact takes up little screen space Precise values can be communicated
Analogue presentation • • •
©Ian Sommerville 2000
Easier to get an 'at a glance' impression of a value Possible to show relative values Easier to see exceptional data values
Software Engineering, 6th edition. Chapter 15
Slide 35
1 01 0 2 0 42 3 D ial w ith nedleP ie chartT herm oetrH orizontal bar
Dynamic information display
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 36
P r e s u r e T e m p e r a t u r e 010203040025507510
Displaying relative values
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 37
T h e f i l e n a m e y o u h a v e c h o s e n h a s b e n u s d . P s c h s n t r m !C h. 16U sO eK r interface d sC ian gcnel
Textual highlighting
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 38
Data visualisation ●
●
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Concerned with techniques for displaying large amounts of information Visualisation can reveal relationships between entities and trends in the data Possible data visualisations are: • • • • •
©Ian Sommerville 2000
Weather information collected from a number of sources The state of a telephone network as a linked set of nodes Chemical plant visualised by showing pressures and temperatures in a linked set of tanks and pipes A model of a molecule displayed in 3 dimensions Web pages displayed as a hyperbolic tree Software Engineering, 6th edition. Chapter 15
Slide 39
Colour displays ●
● ●
Colour adds an extra dimension to an interface and can help the user understand complex information structures Can be used to highlight exceptional events Common mistakes in the use of colour in interface design include: • •
©Ian Sommerville 2000
The use of colour to communicate meaning Overuse of colour in the display
Software Engineering, 6th edition. Chapter 15
Slide 40
Colour use guidelines ● ● ● ● ● ● ● ●
Don't use too many colours Use colour coding to support use tasks Allow users to control colour coding Design for monochrome then add colour Use colour coding consistently Avoid colour pairings which clash Use colour change to show status change Be aware that colour displays are usually lower resolution
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 41
User support ●
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●
User guidance covers all system facilities to support users including online help, error messages, manuals etc. The user guidance system should be integrated with the user interface to help users when they need information about the system or when they make some kind of error The help and message system should, if possible, be integrated
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 42
A p l i c a t o n lintrfapceprM H e E r o m e s a g e s y t e s a g e n t i o n y m lfram H e ps E rot m exsage
Help and message system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 43
Error messages ●
●
●
Error message design is critically important. 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
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 44
Design factors in message wording Context Experience
Skill level
Style Culture
©Ian Sommerville 2000
The user guidance system should be aware of what the user is doing and should adjust the output message to the current context. As users become familiar with a system they become irritated by long, ÔmeaningfulÕ messages. However, beginners find it difficult to understand short terse statements of the problem. The user guidance system should provide both types of message and allow the user to control message conciseness. Messages should be tailored to the userÕs skills as well as their experience. Messages for the different classes of user may be expressed in different ways depending on the terminology which is familiar to the reader. 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. 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. Software Engineering, 6th edition. Chapter 15
Slide 45
Pleas x t lic k Bates , J .OK Can
Nurse input of a patient’s name
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 46
Use System Err or #2 P a . Ba tie Clic k on atie or In vaCanc lid pa ?OK y to or m P aHe tie Re yC System and useroriented error messages
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 47
Help system design ● ● ●
●
Help? means ‘help I want information” Help! means “HELP. I'm in trouble” Both of these requirements have to be taken into account in help system design Different facilities in the help system may be required
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 48
Help information ● ●
●
●
Should not simply be an online manual Screens or windows don't map well onto paper pages. The dynamic characteristics of the display can improve information presentation. People are not so good at reading screen as they are text.
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 49
Help system use ●
●
●
Multiple entry points should be provided so that the user can get into the help system from different places. Some indication of where the user is positioned in the help system is valuable. Facilities should be provided to allow the user to navigate and traverse the help system.
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 50
T enotprylevl taprlyic fartom E n n tm E n resya fgreom syetrm o H elp fram e ntw ork
Entry points to a help system
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 51
H elp fram e m apM M a i l r e d i r e c t i o n n lrp in a m a y b e d a o t h e r e t w o r k u s r y p r e s i n g t h e d c t t o n i t h c o r l a l . T h e s e m a k f m e o f u r o u s e t o w h t m a i l h b n s e n Y o u a r e h r e m o r e n e x t t o p i c s 2 l1 H e p h i s t o r y 4. M .3 a eR S nidr em actioln
Help system windows
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 52
User documentation ●
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As well as online information, paper documentation should be supplied with a system Documentation should be designed for a range of users from inexperienced to experienced As well as manuals, other easytouse documentation such as a quick reference card may be provided
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 53
teF S y s e m S y s t e m N o v i c e E x p e r i n c e d S y s t e m adeuslnucrtpio v ronsaladIm idnson rtcaulm ateioonrsIntm sroadnurcto u u s a d m i n r a o r s r y R e f r e n c A d m i n s t r a o r Õ s l m a u a l g u d e D escrivptco esfH n thestoyinesm o w talG esatrindgdeF ascrilptyonO rm p e antion aced User document types
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 54
Document types ●
Functional description •
●
Introductory manual •
●
Describes all system facilities in detail
System installation manual •
●
Presents an informal introduction to the system
System reference manual •
●
Brief description of what the system can do
Describes how to install the system
System administrator’s manual •
©Ian Sommerville 2000
Describes how to manage the system when it is in use Software Engineering, 6th edition. Chapter 15
Slide 55
User interface evaluation ●
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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
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 56
Usability attributes Attribute Learnability Speed of operation Robustness Recoverability Adaptability
©Ian Sommerville 2000
Description How long does it take a new user to become productive with the system? How well does the system response match the userÕs work practice? How tolerant is the system of user error? How good is the system at recovering from user errors? How closely is the system tied to a single model of work?
Software Engineering, 6th edition. Chapter 15
Slide 57
Simple evaluation techniques ● ●
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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 grip button for online user feedback.
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 58
Key points ●
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●
●
Interface design should be usercentred. An interface should be logical and consistent and help users recover from errors Interaction styles include direct manipulation, menu systems form fillin, 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
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 59
Key points ●
●
●
●
Systems should provide online help. This should include “help, I’m in trouble” and “help, I want information” Error messages should be positive rather than negative. A range of different types of user documents should be provided Ideally, a user interface should be evaluated against a usability specification
©Ian Sommerville 2000
Software Engineering, 6th edition. Chapter 15
Slide 60
