Embed Size (px)
Citation preview
1 CS 501 Spring 2007
CS 501: Software Engineering
Lectures 11 & 12
Usability
2 CS 501 Spring 2007
Course Administration
Quiz 2 on Thursday
Same format as the first quiz
No office hours on Thursday
3 CS 501 Spring 2007
Presentations
Project Presentations
First presentation is next week, Tuesday through Thursday.
Meeting room is at 301 College Avenue.
For instructions, read the Assignments page.
Your client must attend the presentation unless you have special permission.
4 CS 501 Spring 2007
Design
Requirements
Operation andMaintenanceImplementation
Design
Feasibility andPlanning
Your understand the requirements, now to design the system.
5 CS 501 Spring 2007
Software Design
The design phase is the most creative part of software development.
The design must:
• Meet the requirements
• Satisfy the users
• Provide flexibility for changing requirements
• Be suitable for implementation with available resources
• Be testable and maintainable
• Fit within the style of the organization(s)
6 CS 501 Spring 2007
Lectures on Design
Lectures Topic
11-12 Usability
13-14 System Architecture
15-18 Object Oriented Design
7 CS 501 Spring 2007
Reading
Reading: Mitchell Kapor, A Software Design Manifesto. Dr. Dobbs Journal, 1991. http://hci.stanford.edu/bds/1-kapor.html
"Architects, not construction engineers, are the professionals who have overall responsibility for creating buildings. ... in the actual process of designing and implementing the building, the engineers take direction from the architects."
"Software design is not the same as user interface design."
8 CS 501 Spring 2007
The Importance of User Interface Design
Good support for users is more than a cosmetic flourish
• Elegant design, appropriate functionality, & responsive system: => a measurable difference to their effectiveness
• A system that is hard to use: => users may fail to find important results, or mis-interpret what they do find=> user may give up in disgust
A computer system is only as good as the interface it provides to its users
9 CS 501 Spring 2007
Usability: The Design/Evaluate Loop
Evaluate
?Design
Build
Analyze requirements
10 CS 501 Spring 2007
Design for Usability
Usability of a computer system is a combination of factors:
• User interface design
• Functionality
• Performance
• Help systems and documentation
• Freedom from errors
Anything else?
11 CS 501 Spring 2007
Design from a System Viewpoint
interface design
functional design
data and metadata
computer systems and networks
mentalmodel
12 CS 501 Spring 2007
Mental Model
The mental (conceptual) model is the user's internal model of what the system provides:
• The desk top metaphor -- files and folders
• The Web model -- one vast collection of pages with hyperlinks
13 CS 501 Spring 2007
Mental Model
What a person thinks is true about a system, not necessarily what is actually true
• Similar in structure to the system that is represented
• Allows a person to predict the results of his actions
• Simpler than the represented system. A mental model includes only enough information to allow accurate predictions (i.e. no data structures)
Also called conceptual model
14 CS 501 Spring 2007
Interface Design
The interface design is the appearance on the screen and the actual manipulation by the user
• Fonts, colors, logos, key board controls, menus, buttons
• Mouse control or keyboard control
• Conventions (e.g., "back", "help")
Examples:
• Screen space utilization in Acrobat.
• Number of snippets per page in Web search.
15 CS 501 Spring 2007
Principles of Interface Design
Interface design is partly an art; there are general principles:
• Consistency -- in appearance, controls, and function.
• Feedback -- what is the computer system doing? why does the user see certain results?
• Users should be able to interrupt or reverse actions
• Error handling should be simple and easy to comprehend
• Skilled users should be offered shortcuts; beginners should have simple, well-defined options
The user should feel in control
16 CS 501 Spring 2007
Functional Design
The functional design, determines the functions that are offered to the user
• Selection of parts of an object
• Searching a list or sorting the results
• Help information
• Manipulation of objects on a screen
• Pan or zoom
There may be many user interface choices for the same function, e.g., Macintosh v. Windows desktop
17 CS 501 Spring 2007
Data and metadata
Structural data and metadata stored by the computer system enable the functions and the interface
• Effectiveness of searching depends on the type and quality of data that is indexed (free-text, controlled vocabulary, etc.)
• The desktop metaphor has the concept of associating a file with an application. This requires a file type to be stored with each file:
-- extension to filename (Windows and Unix) -- resource fork (Macintosh)
18 CS 501 Spring 2007
Computer systems and networks
The performance, reliability and predictability of computer systems and networks is crucial to usability
19 CS 501 Spring 2007
Non-functional Requirements
Performance, Reliability, Scalability, Security…
Example: Response time0.1 sec – the user feels that the system is reacting instantaneously1 sec – the user will notice the delay, but his/her flow of thought stays uninterrupted10 sec – the limit for keeping the user's attention focused on the dialogue
20 CS 501 Spring 2007
Style of User Interfaces:Command Line Interfaces
User interacts with computer by typing commands
• Allows complex instructions to be given to computer
• Facilitates formal methods of specification & implementation
• Skilled users can input commands quickly
• Requires learning or training
• Can be adapted for people with disabilities
• Can be multi-lingual
• Suitable for scripting / non-human clients
21 CS 501 Spring 2007
Command Line Interfaces
SEARCH I NSPEC Dat abase- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Type keywor ds and pr ess RETURN - - orent er a command
Def aul t i s ADJ : aci d f r ee- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Set #3: aci d adj f r e 0 r ecor ds I NSPEC Dat abase
Set #4: aci d adj f r ee 5 r ecor ds I NSPEC Dat abase
Set #5: aci d and paper 448 r ecor ds I NSPEC Dat abase
Set #6: deaci di f i cat i on 4 r ecor ds I NSPEC Dat abase- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
22 CS 501 Spring 2007
Command line interfaces andText-only menus
Command line interfaces and text-only menus had become almost entirely replaced by graphical interfaces, but are returning:
• Devices with small form factor or other special features, e.g. cell phone, PDA, etc.
• Interfaces for simple tasks with general users, e.g. automated bank teller (ATM)
23 CS 501 Spring 2007
Style of User Interfaces:Graphical interfaces and direct interaction
User interacts with computer by manipulating objects on screen
• Can be intuitive and easy to learn
• Users get immediate feedback
• Not suitable for some complex interactions
• Does not require typing skills
• Straightforward for casual users, slow for skilled users
• Icons can be language-independent
• Difficult to build scripts
• Only suitable for human users
24 CS 501 Spring 2007
Design for Direct Manipulation
metaphors and mental models: Conceptual models, metaphors, icons, but there may not be an intuitive model
navigation rules: How to move among data functions, activities and roles in a large space
conventions: Familiar aspects that do not need extra training.
=> scroll bars, buttons, help systems, sliders
=> good for users, good for designers
look: characteristics of the appearance that convey information
feel: interaction techniques that provide an appealing experience
25 CS 501 Spring 2007
Menus
• Easy for users to learn and use• Certain categories of error are avoided• Enables context-sensitive help
Major difficulty is structure of large choices
• Scrolling menus (e.g., states of USA)• Hierarchical• Associated control panels• Menus plus command line
Users prefer broad and shallow to deep menu systems
26 CS 501 Spring 2007
Help System Design
Help system design is difficult
• Must prototype with mixed users
• Categories of help:
=> Overview and general information=> Specific or context information=> Tutorials (general)=> Cook books and wizards=> Emergency ("I am in trouble ...")
• Must have many routes to same information
Never blame the user!*
27 CS 501 Spring 2007
Information Presentation
Simple is often better than fancy
• Text
precise, unambiguous
fast to compute and transmit
• Graphical interface
simple to comprehend / learn
uses of color
variations show different cases
28 CS 501 Spring 2007
Information presentation: Separation of presentation from content
Information to be displayed
Presentation software Display
Presentation software
Display
Acrobat
html
Firefox
29 CS 501 Spring 2007
System considerations of user interfaces
• Personal computer cycles are there to be used
• Any network transfer involves delay
• Shared systems have unpredictable performance
• Data validation often requires access to shared data
• Mobile code poses security risks
30 CS 501 Spring 2007
Refining the design based on evaluation
Designers and evaluators need to work as a team
Designers are poor evaluators of their own work, but know the requirements, constraints, and context of the design:
• Some user problems can be addressed with small changes
• Some user problems require major changes
• Some user requests (e.g., lots of options) are incompatible with other requests (e.g., simplicity)
Do not allow evaluators to become designers
31 CS 501 Spring 2007
Evaluation
• The process of determining the worth of, or assigning a value to, the usability on the basis of careful examination and judgment.
• Making sure that a system is usable before launching it.
• Iterative improvements after launch.
• Categories of evaluation methods:
– Analytical evaluation: without users
– Empirical evaluation: with users
– Measurements of operational systems
32 CS 501 Spring 2007
Evaluation
How do you measure usability?
Usability comprises the following aspects:
• Effectiveness – the accuracy and completeness with which users achieve certain goals Measures: quality of solution, error rates
• Efficiency – the relation between the effectiveness and the resources expended in achieving themMeasures: task completion time, learning time, clicks number
• Satisfaction – the users’ comfort with and positive attitudes towards the use of the systemMeasures: attitude rating scales
From ISO 9241-11
33 CS 501 Spring 2007
Evaluation without users
Assessing systems using established theories and methods
Evaluation techniques
• Heuristic Evaluation (Nielsen, 1994)
– Evaluate the design using “rules of the thumb”
• Cognitive Walkthrough (Wharton et al, 1994)
– A formalized way of imagining people’s thoughts and actions when they use the interface for the first time
• Claims Analysis – based on scenario-based analysis– Generating positive and negative claims about the effects of
features on the user
34 CS 501 Spring 2007
Measurement
Basic concept: log events in the users' interactions with a system
Examples from a Web system
• Clicks (when, where on screen, etc.)
• Navigation (from page to page)
• Keystrokes (e.g., input typed on keyboard)
• Use of help system
• Errors
May be used for statistical analysis or for detailed tracking of individual user.
35 CS 501 Spring 2007
Evaluation with UsersPreparation
• Determine goals of the usability testing
“The user can find the required information in no more than 2 minutes”
• Write the user tasks
“Answer the question: how hot is the sun?”
• Recruit participants
Use the descriptions of users from the requirements phase to detect potential users
36 CS 501 Spring 2007
Usability Laboratory
Concept: monitor users while they use system
Evaluators User
one-way mirror
37 CS 501 Spring 2007
Evaluation with UsersSessions Conduct
• Conduct the session– Usability Lab– Simulated working
environment
• Observe the user– Human observer(s)– Video camera– Audio recording
• Inquire satisfaction data
38 CS 501 Spring 2007
Evaluation with users:Results analysis
• If possible, use statistical summaries
• Pay close attention to areas where users
– were frustrated
– took a long time
– couldn't complete tasks
• Respect the data and users' responses, don't make excuses for designs that failed
• Note designs that worked and make sure they're incorporated in the final product
39 CS 501 Spring 2007
Evaluation Example: Eye Tracking
40 CS 501 Spring 2007
Evaluation Example: Eye Tracking
41 CS 501 Spring 2007
Evaluation based on measurements
Analysis of system logs
• Which user interface options were used?
• When was was the help system used?
• What errors occurred and how often?
• Which hyperlinks were followed (click through data)?
Human feedback
• Complaints and praise
• Bug reports
• Requests made to customer service
42 CS 501 Spring 2007
Evaluation with Users
Testing the system, not the users!
Stages of evaluation with users:
Preparation
Sessions conduct
Analysis of results
User testing is time-consuming and expensive.
43 CS 501 Spring 2007
Changes in user interface design
Examples of change: 1995 to 2007
44 CS 501 Spring 2007
1990
SEARCH I NSPEC Dat abase- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Type keywor ds and pr ess RETURN - - orent er a command
Def aul t i s ADJ : aci d f r ee- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Set #3: aci d adj f r e 0 r ecor ds I NSPEC Dat abase
Set #4: aci d adj f r ee 5 r ecor ds I NSPEC Dat abase
Set #5: aci d and paper 448 r ecor ds I NSPEC Dat abase
Set #6: deaci di f i cat i on 4 r ecor ds I NSPEC Dat abase- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
45 CS 501 Spring 2007
1995
46 CS 501 Spring 2007
2003
47 CS 501 Spring 2007
2003
48 CS 501 Spring 2007
1995
49 CS 501 Spring 2007
2006
50 CS 501 Spring 2007
1995
51 CS 501 Spring 2007
2003
52 CS 501 Spring 2007
1995
53 CS 501 Spring 2007
2006
