1. [Donald A. Norman, “The Design of Everyday Things,” Chapter 3]
Knowledge in the Head + Mental Models CS Programming Languages for Web Applications
[Donald A. Norman, “The Design of Everyday Things,” Chapter 3]

2. Where is Our Knowledge? Some knowledge for using a UI is in our heads
We use software correctly by merging our knowledge with external influences:
Information in the world – what we see
We often do not need to be precise
Good UIs constrain our use with syntax – electronic connections, radio buttons, elevator buttons
Our culture constrains us – volume and headphones

3. 1. Information in the World
Whose face is on a $20 bill? $50?
We do not need a map to go somewhere we are familiar with
But we might not be able to give directions
And what if we can’t read street signs?
I often forget my classroom numbers after the first week, so use information in he world to find them
How do you remember your 50+ passwords?
I remember to bring my pointer to class by putting it with my notes when I prepare for class

4. Information in the Head Information in the World
Information that we memorize
Our own name
Our address
World
Information that we see or look up
Time
Courses offered next semester
We often move information from one place to another
Our class schedule
The room number for CS 4640

5. Two Types of Knowledge Declarative knowledge: knowledge “of”
Facts and rules: class starts at 2pm, double click the .pptx file icon to open it
Easy to write down and teach
Usually requires memorization
Procedural knowledge: knowledge “how”
Allows somebody to accomplish a task
How to get to class by 2pm
How to find the icon and double click
Much harder to teach and learn
Taught by demonstration and learned through practice
Requires deeper understanding

6. 2. Precision is Not Needed
People are not good at being precise
The 1 dollar coin was almost the same size as a quarter
Remembering 10-digit phone numbers is hard .. So my phone has a contact list and voice activation
The French and Indian war occurred about 20 years before the US revolutionary war .. but which year?
We learn to be precise in our field only after years of learning and practice
A good UI must not require precision
It should help the user find precision when required

7. 3. Syntactic Constraints
Spelling is hard .. but made easier by patterns
What consonants can precede an “h”?
“ch”, “gh”, “ph”, “rh”, “sh”, “th”, “wh”
Singers, musicians, dancers, and martial artists don’t memorize as much as recreate based on patterns that “make sense”
The syntax of a UI must make syntactic constraints clear
In PowerPoint, if I highlight text, lots of actions are immediately enabled

8. Mapping Syntax to Semantics
This arrangement has a natural mapping … fewer mistakes
How can we remember which control maps to which burner ?
Mistakes are encouraged

9. 4. Mental Models Mental: users’ perception of reality
Example distributed file system: files
Implementation: how a machine, virtual or otherwise, is actually built
Example: network protocols
Manifest: how the machine represents the implementation to the user
Example: local disk

10. Example: Driving a Car When we push the gas pedal, the car goes faster
Mental: pushing makes it go faster
Implementation: more gas to the engine, more pressure, pistons go faster, tires go faster …
When we turn the wheel, the car turns
Mental: turning the wheel turns the tires
Implementation: turning the wheel turns something else (with help of a motor for power steering), which causes something else to turn, which puts the tires into a different angle

11. UIs and Mental Models
Telephones: I want to call mom, not xxx-xxxx
Compile: I want to run my program, not compile, link, run
File manager: dragging a file from window to window is
Move on the same disk
Copy from USB thumb drive to disk
Calendars: paper calendars require paging, online calendars can scroll

12. Interfaces should conform to the user’s mental model
UIs and Mental Models
Predicting storms
Does the prediction “30% chance of rain” mean
It will rain in 3 of 10 locations in the area
Less rain than if 50% chance, but more than if 10%
On 3 days out of 10 with these “weather conditions,” it has rained in the past
Dice
If I roll a 6 five times in a row, what is the probability that my next roll will be a 6?
Interfaces should conform to the user’s mental model

13. Summary
Engineers are very comfortable thinking in terms of the implementation model
Users are not!