Lecture 5: Usability Management Flashcards
1
Q
Spiral Model
A
The spiral model was proposed by Boehm in 1987
It consists of 5 activities
- Determine objectives and constraints
- Evaluate alternatives
- Identify risks
- Resolve risks by assigning priorities to risks
- Develop a prototype for the highest identified risk
These 5 activities are applied in rounds (see next slide)
- Each round uses the waterfall model
- If a risk has successfully been resolved, the results are evaluated and the next round is planned
- If the risk could not be resolved, the project is terminated immediately.
2
Q
Spiral model picture
A
3
Q
Limitations of Linear and Iterative Models
A
- Linear and iterative models do not deal well with frequent change
- The Waterfall model assumes that once you are done with an activity, all issues covered in that activity are closed and cannot be reopened
- The Spiral model can deal with change between activities, but does not allow change within an activity
- What do you do if change is happening more frequently?
4
Q
Change influences choice of process model
A
- Three definitions •
- PT = Project Time
- TBC = Time Between Change
- MTBC = Mean Time Between Change
5
Q
Changes and models
A
- No change during project
- MTBC » PT
- Waterfall model, V-model
- Infrequent changes during the project
- MTBC ≈ PT
- Spiral model, Unified Process
- Changes are frequent
- MTBC « PT
- Agile Process.
6
Q
Why Prototyping?
A
- Instant gratification
- Tangibility
- A prototype helps to understand a system early
- • Improves poor communication
- • Allow early decision making
- • Mistakes are found early
- “We want instant prototypes. They allow us to make more mistakes faster”
- Elaine Hunt, Clemson University
- “We want instant prototypes. They allow us to make more mistakes faster”
7
Q
Failures are helpful
A
- Henry Petrovski’s paradoxical approach to design:
- Better information comes from designs that fail than from those that succeed
- Reason: failures draw more scrutiny. Petrovski says without failure, complacency sets in.
- Famous quote from Petrovski: „Success in Engineering is defined by its failures“.
8
Q
Knowledge must be falsifiable
A
- Karl Popper (“Objective Knowledge”):
- There is no absolute truth when trying to understand reality
- One can only build theories, that are “true” until somebody finds a counter example
- The truth of a theory is never certain
- We can only use phrases like: “by our best judgment”, “using state-of-the-art knowledge”
- Falsification: The act of disproving a theory or hypothesis.
9
Q
Consequence for Software Systems
A
- In software engineering any system, including a user interface, is a model and thus a theory:
- We build models to find counter examples by:
- Requirements validation, user interface testing, review of the design, source code testing, system testing, etc.
- Testing: The act of disproving a model
- We build models to find counter examples by:
- Usability Testing: The act of testing a user interface
- We can do these tests with prototypes.
10
Q
A Misnomer: Rapid Prototyping
A
- Revolutionary prototyping has sometimes been called rapid prototyping
- The term rapid prototyping should not be used
- It confuses prototyping with rapid development
- Prototyping is a technical issue: It is a particular life cycle process model
- Rapid development is a management issue. It is a particular way to control a project
- Prototyping can go on forever if it is not restricted
- “Time-boxed” prototyping limits the duration of the prototype development.
11
Q
Horizontal vs. Vertical Integration
A
12
Q
2 Types of Prototyping Activities
A
- Revolutionary Prototyping
- Also called specification prototyping
- Develop a prototype to get the requirements right, then throw the prototype away, and develop the whole system from scratch
- Advantage: The prototype can be developed in a short amount of time
- Disadvantage: Users may like features in the prototype that are very expensive to implement
- Evolutionary Prototyping
- The prototype is used as the basis for the development of the final system (nothing is thrown away)
- Advantage: Short time to market
- Disadvantage: Evolutionary prototyping can be used only if the target system can be constructed in the prototyping language.
- The prototype is used as the basis for the development of the final system (nothing is thrown away)
13
Q
3 Types of Prototypes
A
- Illustrative Prototype
- Develop the user interface with a set of storyboards
- Implement them on a napkin or with a user interface builder
- Good for a first dialog with the client •
- FunctionalPrototype
- Implement and deliver an operational system with minimum functionality
- Then add more functionality, order identified by risk
- Good for incremental development
- Exploratory Prototype (“Hack”)
- Implement part of the system to learn more about the requirements
- Good for paradigm breaks.
14
Q
Prototyping Techniques
A
- • Hapticprototypes
- • Paperprototypes
- • Wireframe prototypes (also called Mock-ups)
- • Term from 3D computer graphics
- • Used for the schematic presentation of a screen or webpage
- • Storyboard
- • Sequence of Wireframes
- • Low and High fidelity prototypes •
- Scenario based video prototypes •
- Wizard of Oz Prototyping
15
Q
wizard of oz prototyping
A
- Also called Wizard of Oz experiment
- • Tool Support: SketchWizard [Davis et al 2007]
- • System Status:
- • User Interface ready for testing
- • Functionality is not completely done
- • User interacts with the system
- • Functionality is replaced by a real person also called Wizard, who is not visible to the user
- • User believe the system to be finished but it actually is operated by the Wizard.
16
Q
Managing expectations
A
If you show end users (especially non programmers) a screen which has an unfinished user interface, they will think that the program is unfinished
If you show end users a screen which has a polished user interface, they will think the program is almost done.
17
Q
Evaluating Prototypes
A
- Heuristic Evaluation can already be used for the evaluation of Prototypes
- It can start early in the development process, does not have to wait for the final product
- Heuristic evaluation works on
- Sketches
- Paper prototypes
- Unstable prototypes
- “Missing-element” problems are harder to find on sketches
- Because you’re not actually using the interface, you aren’t blocked by feature’s absence
- Look harder for them.
18
Q
Risks of Prototyping
A
- Developer may become attached to the prototype
- Excessive development time of the prototype
- Customer might not appreciate how much work must be done to turn a prototype into a fully functioning system
- User may confuse between prototype and finished system
- Prototype may actually perform the functions it implements better than a fully functional deliverable
- Negative feelings toward the software if prototype has problems
- Cost of implementing the prototype.
19
Q
Definitions usability
A
- Usability: Measures how well a user can use the system functionality. Is measured by several categories
- Learnability: A system is more usable if it is easier/faster to learn than another system
- Number of steps: A system is more usable than another system if requires less steps to accomplish a particular task
- “The system is easy to use”: One of the most frequently misused terms, especially in advertising. Often these systems are actually unusable.
- Unusability: The user has extreme difficulties to learn or to use the system.
20
Q
User Interfaces Are Hard to Design
A
- Developer is not equal to user
- Software engineers communicate mostly with other developers
- User Interface development is about communicating with users
- The user is always right
- Consistent problems are the system’s fault
- ….but the user is not always right
- Users are not designers
- User interface takes a lot of software development effort
- • ~50% of Design, Implementation and Maintenance
- Managers must be involved (Usability management).
21
Q
Usability Management
A
- Usability is Multidimensional
- Learnability
- Is the user interface easy to learn?
- Efficiency
- Once it learned learned, is it fast to use?
- Memorability
- Is it easy to remember what the user has learned?
- Error handling and Robustness
- Are errors recoverable?
- Satisfaction(Userexperience)
- Is the user interface enjoyable to use?
22
Q
Properties of the motor processor
A
- • Imagine you have to grab a bottle or a paper clip
- Moving your hand to the target is a sequence of corrections
- You are overshooting or undershooting your hand while you are trying to reach the target
- Fitts’sLaw(PaulFitts,1954)
- Specifies how fast you can move your hand to a target of a certain size at a certain distance (within arm’s length)
- The Time T to move your hand to a target of size S at distance D away is:
- • T=a+blog(D/S+1)
23
Q
Consequences of Fitts’s Law
A
- Targets at the screen edge are easy to hit
- You do not need a correcting cycle to hit it
- Unclickable margins are foolish
- Hierarchical menus are hard to hit
- Too many correction cycles
- Gimp/GTK: instantly closes menu (< 100 ms)
- Windows: 500 ms timeout (exceeds Tp even for Slowman)
- Chrome does it right: triangular zone
- • Pie menus are faster than popup menus
- • Each menu item is the same distance D away from the mouse pointer.
24
Q
Noise in Communication (ctd)
A
- When projects become more complex, many choices have to be made
- You will experience even more conflicts between your different learned simplification systems
- Therefore you have to make even more decisions
- If you don’t understand the requirements or the technology of a system, your old learned preferences may unconsciously make decisions for you.
25
Usability Testing
* Usability Testing: Watching a user interact with the user interface of the system
* Usability testing uses scenario-based design: Involves the creation of a test scenario, where the user performs a list of tasks while the observer watches and takes notes, and compares the observed with the specified behavior
* Heuristic Evaluation:
* A usability engineering method to find usability problems in a user interface design
* The difference between usability testing and heuristic evaluation is similar to the difference between walkthrough and inspection.
26
Models in User Interface Design
Three models are relevant to the UI Designer
* • System Model: how the system really works
* • (User) Interface model: Model of the system presented to the user
* • User Model: How the user thinks the system works
27
User Models are often Incorrect
* Users with incorrect user models cannot be dismissed
* Remember: The user is always right J
* To understand this problem and to deal with it, we add another model:
* Design Model: Model in the designer’s head realized in the Interface model
28
How can the Design Model be Communicated to the User? (Norman)
* Users rely on clues in order to learn from the design model
* the parts that make up the interface
* How these parts work together
* Example of clues we take from our interaction with physical objects
* • Natural mapping •
* Affordances
* • Constraints •
* Visibility
* • Feedback
29
Natural Mapping
Natural Mapping (also called direct mapping): Physical arrangement of controls should match arrangement of the objects to be controlled
* Light switch panel
* How does each switch correspond to the light it controls? If the switches are arranged similar to the lights, the controls are much easier to learn
* Stoves
* Which knobs control which burner? Most stoves don’t make any attempt to provide a natural mapping.
30
Affordance
* Affordance refers to the perceived and actual properties of a thing
* In particular the properties that determine how the thing could be operated (dynamic model)
* Perceived and actual properties of an object determine how it can be used
* A chair is for sitting
* A button is for pushing
* A knob is for turning
* A menu is for selection
* A scrollbar is for continuous scrolling or panning.
31
Managing Human Error
* Two major categories
* Mistake: Trying to do something the system cannot do
* Caused by users with the wrong User Model •
* Typically made by novice users
* Slip: wrong execution
* Typically made by expert users when distracted, bored or under stress
* 3 Types of slips:
* • Description error •
* Capture error
* • Mode error
* Slips can be prevented by a good Design Model.
32
Slip Example: Description Error
Description Error: Happens when two actions are very similar. The intended action is replaced by another action with many features in common
* Pouring orange juice into your cereal
* Putting the wrong lid on a jar
* Mustard lid on the strawberry jar
* Design Model recommendation: Avoid actions with very similar descriptions
* Don’t design long rows of identical switches.
33
Slip Example: Capture Error
* Capture Error: A sequence of actions is replaced by another sequence that starts the same way
* Leave your house and find yourself walking to the grocery instead of where you meant to go
* Design Model recommendation: Avoid habitual action sequences with common prefixes.
34
Slip Example: Mode Error
* Mode Error: States in which actions have different meanings
* Examples:
* Insert mode vs. command mode in the VI editor
* Insert mode: Letters are inserted into the text file
* Command mode (default): Letters invoke editing commands
* Caps Lock:
* User wants to type lowercase letters but doesn’t notice that Caps Lock is enabled
* Tricky when you are typing a password
* Design Model Recommendation:
* By all means try to eliminate modes
* If modes are necessary make them visible
* Temporary modes: Spring loaded shift key.
35
10 Heuristics for Managers and User Interface Designers (Nielsen)
1. 1. Match the Real World
2. 2. Maintain Consistency
3. 3. Provide good Help and Documentation
4. 4. User Control and Freedom
5. 5. Visibility of System Status
6. 6. Flexibility and Efficiency
7. 7. Error Prevention
8. 8. Recognition, Not Recall
9. 9. Error Reporting, Diagnosis and Recovery
10. 10. Aesthetic and Minimalist Design.
36
Chunking Nielsen’s Heuristic into 4 Categories
* Meet expectations
* 1. Match the real world
* 2. Consistency & standards
* 3. Help & documentation
* The user is the boss
* 4. User control & freedom
* 5. Visibility of system status
* 6. Flexibility & efficiency
* Handleerrors
* 7. Error prevention
* 8. Recognition, not recall
* 9. Error reporting, diagnosis, and recovery
* Keep it simple
* 10. Aesthetic & minimalist design
37
A revolutionary prototype
Select one or more:
a. Is also called a specification prototype
b. Takes long time to be developed
c. Helps to understand the requirements
d. Acts as first potentially shippable product increment
e. Is only used in traditional lifecycle models
f. Is always a horizontal prototype
a, c
38
Which risks should be considered when prototyping?
Select one or more:
a. Prototyping leads to early feedback
b. A customer can think the system is already finished if he sees the prototype
c. Prototyping may become expensive
d. Fancy prototypes can increase costumer expectations
e. A prototype with problems induces bad feelings for the real system
b,c,d,e
39
Horizontal Prototypes
Select one or more:
a. Show small range of features
b. Have full implementation of features
c. Are used in agile processes
d. Can follow a bottom up integration approach
d
40
Which of Nielson's heuristics belong to the category "Meet expectations"?
Select one or more:
a. User control & freedom
b. Help & documentation
c. Match the real world
d. Clearly marked exits
e. Use Metaphors
f. Error prevention
b,c,e
41
Which of the following statements about Models in UI Design are correct?
Select one or more:
a. The Interface Model should be easy to understand and should not hide the system model
b. The System Model describes the system presented to the user
c. The User Model illustrates how the systems works from the perspective of the developer
d. The Design Model influences the Interface Model
e. Affordances help to communicate the design model to the user
Which of the following statements about Models in UI Design are correct?
Select one or more:
a. The Interface Model should be easy to understand and should not hide the system model
b. The System Model describes the system presented to the user
c. The User Model illustrates how the systems works from the perspective of the developer
d. The Design Model influences the Interface Model [Correct]
e. Affordances help to communicate the design model to the user [Correct]
