User interface design

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 1

Topics covered

  Design issues • • User interaction Information presentation The user-centered design process • • • User analysis User interface prototyping Interface evaluation Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 3

Three-Mile Island nuclear accident

   Nuclear power plant located on Susquehanna River, Pennsylvania.

On March 28, 1979, the Unit 2 reactor suffered a partial core meltdown.

Incident started with a valve failure, but escalated into full-blown emergency, partly because operators misinterpreted the control panel indicators. Unit 2 is the pair of towers to the right.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 4

Three-Mile Island nuclear accident

Control Room Maintenance tags

Panel after panel of multicolored indicator lights plus audible alarms. In the emergency, it was impossible to tell which alarm was According to testimony, a tag covered a crucial valve indicator light during the first 8 minutes of the accident.

Software Engineering, 7th edition. Chapter 16

Slide 5

User interface design issues

    User interfaces should be designed to match the skills, experience and expectations of its anticipated users.

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 6

Human factors in interface design

    Limited short-term memory • 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 • 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 • People have a wide range of physical capabilities. Designers should not just design for their own capabilities.

People have different interaction preferences • Some like pictures, some like text.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 7

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 short-term memory) and should recognise that people make mistakes.

UI design principles underlie interface designs although not all principles are applicable to all designs.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 8

User interface design principles

Principle

User familiarity Consistency Minimal surprise Recoverability User guidance User diversity

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 context-sensitive user help facilities.

The interface should provide appropriate interaction facilities for different types of system u ser.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 9

Design principles

   User familiarity • The interface should be based on user-oriented 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.

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 Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 10

Design principles

   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. For example, some users have seeing difficulties and so larger text should be available Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 11

Interaction styles and information presentation

  Two problems must be addressed in interactive systems design • Maximizing user-to-computer information bandwidth.

• How should information from the user be provided to the computer system?

• What is the best (most efficient) way for the user to interact with the computer? • Maximizing computer-to-user information bandwidth.

• How should information from the computer system be presented to the user?

• What is the best (most effective) way for the user to comprehend the computer’s output?

User interaction and information presentation may be integrated through a coherent framework such as a user interface metaphor.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 12

  

Efficiency model for user-computer communication

User starts input User initiates activity Computer begins response Computer completes response User starts input Response time Prep time Think time

Intervals • System response time – the time it takes the computer to process the user request (depends on system performance) • User think time – the time a user spends digesting the output of the computer • Input prep time – the time it takes a user to communicate his intent to the computer Increased user-computer bandwidth  Increased computer-user bandwidth  Decreased input prep time Decreased user think time Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 13

Interaction styles

     Direct manipulation Menu selection Form fill-in Command language Natural language Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 14

Interaction styles

Interaction style

Direct manipulation Menu selection Form f ill-i n Command language

Main advantages

Fast and intuiti ve interaction Easy to learn Avo ids user error Little typing required

Main dis advantages

May be hard to impleme nt.

Only suitable wher e there is a visual metapho r for tasks and objects.

Slow for expe rienc ed users.

Can become complex if many menu options.

Simple data entry Easy to learn Checkable Takes up a lot of screen space.

Cause s problems whe re user options do no t match the form fields.

Powerful and flexible Hard to learn.

Poor error manage ment.

Natural language Accessible to casual users Easily extended Requires more typing.

Natural la nguage und erstand ing systems are un reliable.

Appli cation exampl es

Video games CAD systems Most general purpose systems Stock control, Persona l loan processing Operating systems , Command and control systems Info rmation retrieval systems Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 15

Navigation

    Navigation is the way the user interacts with the computer to access the features and facilities of an application.

Usually done via keystrokes, mouse clicks and movements.

Goal: minimize the amount of navigation Some types of navigation • Between multiple screens • Most disorienting form of navigation • Between multiple frames or panes • Can be a problem if too many are on one screen • Between tools and menus in a page • Frequently performed tasks can lead to repeated movements which slow down productivity and present a health hazard • Within information displayed in a page (scrolling, panning, zooming, etc) • Information outside the screen range is often forgotten Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 20

Improving navigation of web pages

 Tips • • Reduce the number of places to go • Minimize number of pages to accomplish a function (2-3) Provide overviews (“breadcrumb trails”)

Books > Subjects > Computers > Programming > Java

• Provide appropriate mapping of controls to functions

Sort “Most Recent First” instead of “Descending Order”

• Customize the interface to match user needs • Place most frequently used functions in the most convenient locations • Avoid deep hierarchies Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 21

Information presentation

    Model-view-controller paradigm Presentation styles Color management Error messages Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 22

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 Model-View-Controller approach is a way of supporting multiple presentations of data.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 23

Information presentation

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 24

Model-view-controller

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 25

Model-view-controller

   Model: Responsible for application domain knowledge (repository) View: Responsible for displaying application domain objects to the user Controller: Responsible for sequence of interactions with the user and notifying views of changes in the model (control flow) Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 26

MVC example sequence

Windows : WindowSystem 3: clicks mouse 4: mouseDownEvent() 5: request() 1: subscribe() 2: subscribe() 6: notify() 7: getData() 8: data 9: update() 10: update() 11: reads changes 12: notify() 13: getData() 14: data 16: update() 17: reads changes 15: update() Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 27

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?

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 29

Alternative information presentations

Jan 2 8 42 Feb 28 51 M ar 3 16 4 Ap ril 2 78 9 M ay 12 73 June 2 83 5 4000 30 00 2 0 00 1 0 00 0 Jan Feb M ar Ap ril M ay June Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 30

3-D information presentation

1500 1000 500 0 3500 3000 2500 2000 Jan Feb Mar April May June Poor choice: 3 rd dimension does not add any information (“chartjunk”) Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 31

Analogue or digital presentation?

  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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 32

Presentation methods

4 1 3 2 Dial wit h needle 0 10 Pi e ch art Th er m om et er Ho rizon t al bar 20 Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 33

Displaying relative values

0 1 00 Pressur e 200 300 40 0 0 2 5 Temp er at ur e 5 0 75 100 Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 34

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: • The use of colour to communicate meaning; • The over-use of colour in the display.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 36

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 37

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 38

Design factors in message wording

Factor

Context Experience Skill level Style Culture

Description

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. As users become familiar with a system 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. Messages should be tailored to the user’s skills as well as their experience. Messages for the different classes of user may be expressed in different ways depending on the terminology that 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. Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 39

User error

 Assume that a nurse misspells the name of a patient.

Please type the patient’s name in the box then click OK P atient’s name MacDonald, R.

OK Cancel Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 40

Good and bad message design

System-orient ed error message Error #27 Invalid patient id OK Cancel User-orient ed error message

R. MacDonald is not a registered patient

Click on Patients for a list of patients Click on Retry to re input the patient’s name Click on Help for more information Patients Help Retry Cancel Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 41

User-centered design process

  UI design is an iterative process involving close liaisons between users and designers.

The 3 core activities in this process are: • User analysis . Understand what the users will do with the system; • System prototyping . Develop a series of prototypes for experiment; • Interface evaluation . Experiment with these prototypes with users.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 42

User-centered design process

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 43

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 44

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 45

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 46

User analysis activities

    Ideally performed during requirements elicitation. Task analysis • • • Models the steps involved in completing a task. Functional decomposition of user tasks.

Forms the basis of user menus and screens.

Interviewing and questionnaires • Asks the users about the work they do.

Ethnography • Observes the user at work.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 47

Hierarchical task analysis

3 .1

1 Disco ver p ossible so urces Select li brary 3 .2

Lo g in t o cat al ogue 3 .3. 1 Ret riev e pict ures fro m rem o t e li braries do 1, 2, 3 unt il pi ct ures fo un d, 4 2 Est ablish search t erm s 3 Search for p ict ures 4 .

Request p ho t ocop ies of found items do 3.1 , 3 .2 , 3 .3 un t il pict ures foun d, 3 .4 if n ecessary, 3.5

Enter search t erm s 3 .3

Search for p ict ures 3 .4

M odify search t erms 3 .3. 2 do 3.3 .1 , 3 .3. 2, 3.3 .3

In it iat e search 3 .3. 3 Rev iew result s 3 .5

Record relevan t it em s Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 48

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 51

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 52

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: • Early in the process, paper prototypes may be used; • The design is then refined and increasingly sophisticated automated prototypes are then developed.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 53

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 54

Prototyping techniques

   Script-driven prototyping • 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 • Use a language designed for rapid development such as Visual Basic. Internet-based prototyping • Use a web browser and associated scripts.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 55

User interface evaluation

    Also known as

usability testing

.

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 56

Usability attributes

Attribute

Learnability Speed of operation Robustness Recoverability Adaptability

Description

How long does it take a new user to become productive with the system? How well does the system response match the user’s 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? Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

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 code in the software to collect on-line user feedback.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 58

Usability testing

 One variant • • Method: think-aloud test System under test: • • Real system – carry out various tasks Prototype – evaluate window contents and navigation • Team • • • Facilitator – talks with the user Log keeper – records the test session Observer – extra

Software Engineering, 7th edition. Chapter 16

Slide 59

Usability testing: “Think-aloud” protocol

Purpose: Find usability problems I try this because ...

User doesn’t notice ...

Facilitator Listens Asks as needed Logkeeper Listens Records problems User Performs tasks Thinks aloud Software Engineering, 7th edition. Chapter 16

Slide 60

Usability testing steps

   Planning the test • Choose test users • Typical users for the system.

• Don’t select other developers (unless it is an application to be used by developers).

• Choose test tasks • Real work situation – select some realistic scenarios for the user to perform.

Carry out the test • Explain the purpose clearly to the user.

• It is the system that is being tested, not the user.

• • • Assign the task • Remind user to think aloud by explaining what he does and why Observe and record the user’s actions and words.

Offer help when user asks for it.

• As much as possible, leave user alone to struggle with the task.

Reporting the results • Condense the issues found into a list of problems.

• This should be done as early as possible, within 12 hours, while your memory is fresh.

Software Engineering, 7th edition. Chapter 16

Slide 61

Usability problems

   Anything about the application that hampers a user in performing his task.

Usability problems are a special kind of software defect. The system works as intended by the developer, yet the user finds it hard to get useful work out of the system.

Examples of severity classes: • Missing functionality – the system cannot support the user’s task.

• • Task failure – the user fails (knowingly or unknowingly) to complete the task on his own.

Annoying – the user complains that the system is cumbersome.

• • Medium – the user succeeds after stumbling around for a long time.

Minor – the user succeeds after a few attempts.

Software Engineering, 7th edition. Chapter 16

Slide 62

Examples of usability problems

 The system works as intended by the developers, but the user: • • • • • “Cannot figure out how to start the search. Finally finds out to use F10.” “Believes he has completed the task, but forgot to push Update.” “Sees the discount code field, but cannot figure out which code to use.” “Says it is crazy to use six screens to fill in ten fields.” “Wants to print a list of discount codes, but the system cannot do it.”

Software Engineering, 7th edition. Chapter 16

Slide 63

Key points

    User interface design principles should help guide the design of user interfaces.

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.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 64

Key points

    The user interface design process involves user analysis, system prototyping and prototype evaluation.

The aim of user analysis is to sensitise designers to the ways in which users actually work.

UI prototyping should be a staged process with early paper prototypes used as a basis for automated prototypes of the interface.

The goals of UI evaluation are to obtain feedback on how to improve the interface design and to assess if the interface meets its usability requirements.

Modified from Sommerville’s originals

Software Engineering, 7th edition. Chapter 16

Slide 65