SY DE 542

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SY DE 542Basic Design of Info Req’ts

The Language of Interface Design

Jan. 24, 2005

R. ChowEmail: [email protected]

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TA

• Munira Jessa

• Tel: xtn 4904

• Email: mnjessa@engmail

• Office: E2 1303N (AIDL)

• Will grade Checkpoints # 3,4,5; one of the two reports

• Between lectures, contact Munira FIRST for any course-related questions

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Case Study: Apollo 13

• April 1970

• NASA’s 3rd mission to carry humans to lunar surface

• Oxygen tank explosion

• Oxygen stores depleted within 3 hours; loss of water, electricity, propulsion system

• Mission aborted but crew returned safely

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Apollo 13

• Mission controllers took 54 minutes before realizing that oxygen tank had exploded, and command module was dying …

• Why??

• Look at snapshots of actual Mission Control screens and try to locate relevant data values …

(Woods, Patterson, Corban, in press)

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Apollo 13 Discussion• Why was the explosion hard to spot?

– No History / Trend information• Previous value• Increase / decrease / constant• Rate of Increase / decrease

– No Limits / Critical Values information• Maximum allowable value• Normal value

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Context• A background for reading data

• Turns data into information (with meaning)

• Examples:– UV rating of 6– Test score of 27– Output temperature of 30 deg C (DURESS)

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Single Variable Constraints

• Start with list of variables for each AH level

• For each variable, ask:– What are the Limits? Min. / Max. / Both?– What is High vs. Low?– What is Good vs. Bad?– What is Safe vs. Unsafe?

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Context (cont’d)

• Besides high vs. low, normal vs. abnormal– Point where action can be taken– Point where action will be taken (e.g., by

automation)– Point where action must be taken

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Design Implications

• Scale Ranges

• Alarm Limits

• Important Thresholds

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Redesigning Apollo 13 Displays

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Redesigning (cont’d)

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Redesigning (cont’d)

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Apollo 13 Discussion (cont’d)

• Why else was explosion hard to spot?– Data overload

• Many data values• Need for simultaneous monitoring• Need for continuous monitoring• Critical events may be of short duration

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Salience

• What “stands out” in an interface

• Consider what user needs first, second, third …

• Direct attention accordingly

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Designing for Salience

• Colour

• Large size

• Centred

• Moving

• Flashing

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Salience (cont’d)

• What is more salient?– Red or Grey?

– Neon Green or Dark Green?

– High-pitch or Low-pitch Sound?

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Salience: Example 1

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Salience: Example 2

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Salience (cont’d)

• Salience is relational

• Each new form added changes the salience of all others

• Direct attention, not monopolize

• Salience as a need, not as a rule

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Levels of Visual Information Representation

• Graphic Atoms

• Graphic Fragments

• Graphic Forms

• Views

• Workspaces

(Woods, 1997)

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• Smallest unit

• A letter, digit, line, colour block

• Design decisions: – colour, – size, – shape, – length, – thickness, – angle, etc.

Graphic Atom

A

3

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Graphic Fragments• Words, numbers, bars, scale, labels

• Design decisions: – position, – content of numbers, words – relation to near fragments, (proportion, salience)– forms of reference

temperature

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Forms of Reference

• Different kinds of mappings between:

• Visual Form– what something looks like

• Representational Form– how it conveys meaning about the world to a

user

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Visual and Representational Form

Visual Token (an atom or a fragment, etc.):

• has a visual form & a representational form

Visual Token:

• Word: e.g., Temperature

Visual Form:

• Black, Arial font, lines and curves

Representational Form:

• a variable, a measure of heat

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Forms of Reference

• 3 kinds

• 1) Propositional

• 2) Iconic

• 3) Analogical

• Describe how the visual token relates between the user and the world

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Propositional Form

• Relation between the token and the world is arbitrary

• Token tells the observer about the world• Typically words, numbers, some graphics• Relies on stored knowledge such as

language, numbers• Gives current state but little more

Observer Token World“tells” arbitrary

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Iconic Forms

• Depends on quality of visual form to look like the world

• Token should evoke recognition

• Relies on observer experience with the world

• Typical “icons”

Observer Token Worldrecognizes looks like

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Analogical Forms

• May or may not look like world

• Typically graphs on contextual backgrounds

Observer Token Worldprocesses constraint

captures natural constraint

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Examples

• Stop light

propositional

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Airline departure and arrival signs

iconic

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Stop Sign

STOP propositional

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Stove Labels

“REAR”

“FRONT”

propositional

iconic

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Mixed Forms of Reference

– iconic– propositional– iconic

• Windows Recycle Bin– Recycle Bin– darkens/lightens– fills/empties

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Map• Words

• Symbols

• Landmark Images

• Spacing and Scale

• Propositional

• Propositional

• Iconic

• Analogical

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Forms of Reference: Summary

• Propositional and Iconic usually give 1 piece of information

• Analogical usually gives many pieces

• Representation is not right or wrong but changes the work of the observer

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Work involved in processing representations

• Analogical perceptual

• Propositional memory

• Iconic recognition memory

• (Propositional and Iconic both rely to some degree on knowledge in the head. Analogical leaves knowledge in the world.)

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Graphical Forms

• Graphs, Indicators

• Convey meaning

• Design decisions:– Analog or digital forms– Context– Salience

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Analog vs. Digital

• Digital:– uses propositional reference

– set of numerical strings that describe the referent e.g. 100.91

– observer reads the information

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Digital Forms

• often only current state is available• very difficult to display history of the

referent• past or future states must be

– remembered– calculated– displayed separately

• memory and mental workload for user

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Design Requirements

• Label/Identifier

• The Value itself

• Precision (# of significant digits)

• Showing context – Normal / Abnormal?– Max / Min?– Change?

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Showing Context with Digital Forms

123.45 Change the colour of the numbers for meaning e.g. red for alarms

150.55

123.45Arrows to show rate and direction of change

123.45 Ratios to show performance relative to a target value

123.45

123.45 C Units also add context

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Analog

• uses analogical reference

• data is represented by a relationship between visual tokens on the screen

• representation is not as direct as digital

• requires the interpretation of a position in space

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Analog

• Relationship is typically between:– an indicator, and

– a reference scale

• Reference scale = Frame of reference

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Aspects of Analog Forms

• Movement of the indicator is in space and relative to landmarks

• Landmarks are ticks, labels etc.

• Movement depends on the type and grain of the scale

• There are multiple possible frames of reference

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Frames of Reference

1-dimensional frame of reference

indicator

scale

2-dimensional frame of reference

scales

indicator

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Design Requirements

• Scale range (max, min, offscale, failed)

• Reference values

• Indicator, labels, scales

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Possible Reference Values

1. Value vs. its past values– changes over time, rate of change

2. Value vs. its future values– predicted values

3. Value vs. its target value (or range)– Setpoints

4. Value vs. alarm limits/max/min values5. Value vs. key decision points

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In terms of Workload• Analog is generally easier for decisions

made against a referent, done perceptually

• Digital requires mental comparisons and memory in this situation

• Digital needed when accuracy required

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The Principle of Primacy of Perception

• Whenever you can offload a mental task to a perceptual task you take advantage of human capabilities and make work easier.

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Analog Example:Polar Star Display

scale

Current value

High limit

Low limit

One scale Multiple scales put together

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Other Analog Forms

• Combined with digital

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Stacked Bar Graphs

- another example of multiple analog forms

v1

v2

v3

v4

Height=v1+v2+v3+v4

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“Icons” that are Analog

Icon “fills” with water to show level

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More analog forms

Degree of rotation shows degree valve is open.

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Checkpoint #3 (due Jan.31)Information Availability

• Extract a list of variables for each AH level

• For each variable, determine if it is:– Currently Available

• Directly sensed?

• Calculated from sensor data?

– Currently Unavailable• Can be calculated from sensor data?

• Can be sensed? (If so, will sensor be added?)

• Cannot be sensed or calculated?

• (If so, using a heuristic/substitute measure?)

• Submit in Tabular format