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Transcript of Interface Design
Primary goal of interface design
: how well users can use the system’s functionality.
– Learn-ability: is it easy to learn?
– Efficiency: once learned, how fast is it to use?
– Memorability: is it easy to remember how to use?
– Errors: are errors few and recoverable?
– Satisfaction: is it enjoyable to use?
Priority of Dimensions Varies
We can measure & compare on each dimension.
Depends on the user:
– Novice users need learnability
– Infrequent users need memorability
– Experts need efficiency
Users are not uniformly novice/expert
+ users change over time
Depth of domain knowledge
Depth of application knowledge
"I know synthesis, but not how to use your program"
"I'm an expert Logic user but have never used a software synth."
Know Thy User
Cheap, throw-away implementations
analysis w/ heuristics
analysis w/ models, tests
observe users trying it out
again, and again, and again...
Why iterative design?
Why not get it right and finish it?
"Waterfall" Design Model
Lack of feedback up the waterfall!
Ex.: verification finds a new feature/requirement: work has to rewind to the earliest stages.
Waterfall is bad for UI design:
UI design is Risky
We're likely to get it wrong the first few times.
User Evaluation at All Stages
Users are the "gold standard" and will reveal issues at all points.
Changes have Big Impacts
UI changes can have wide ramifications on the whole system.
Parallel design is feasible: build & test multiple prototypes to explore design alternatives
• Later iterations use richer implementations, after UI risk has been mitigated
• Every prototype is evaluated – Users involved in all iterations
• More iterations generally means better UI
• Only mature iterations are seen by the world
• Early iterations use cheap prototypes
Iterative Design Using the Spiral Model
First Step in User-Centered Design
Who is the User?
What does the user need to do?
Identify characteristics of target user population:
– Age, gender, ethnicity
– Physical abilities
– General computer experience
– Skills (typing? reading?)
– Domain experience
– Application experience
– Work environment and other social context
– Relationships and communication patterns
May have many types of users!
What is interface design?
Dimensions of usability
Identify Individual Tasks
actions/sequences the program or interface might solve
Each Task is a Goal
Start with Overall Objective
then decompose into smaller, and smaller tasks
more and more specific.
Identifying a Task
What needs to be done?
What must be done to make it possible?
What steps are involved in doing the task?
can be decomposed
Replicating a bad feature
Ignoring a good feature
may be inefficient, but common-place
learned, but expensive/error-prone
ignore innovation due to convention
focus on WHY not How
features that are rarely used may be critical in certain situations
keep the baby, not the bath water
know what is needed and what should be changed!
for better task analysis
Why do you do this?
What's the goal?
How do you do it?
Look for Weaknesses
in current situation
What aggravates you?
Failures? Errors? Wrong results?