Transcript No Slide Title

Tenix Defence
Universal Principles of Design
Prepared by:
Anthony Royle
Systems Engineer
Approved by:
Malcolm G. Tutty
P-3 CENGR
August 2006
Tenix Defence
Presentation Brief

Design is a diverse discipline

We apply a very specific subset

This presentation will introduce concepts
which should be considered when designing

For details of specific topics, refer to:
Universal Principles of Design
William Lidwell, Kritina Holden, Jill Butler
ISBN1-59253-007-9
Tenix Defence
80/20 Rule
A high percentage of effects in a large system are caused by a low
percentage of variables

80% of a products use involves 20% of its features
 80% of progress is from 20% of the effort

80% of errors come from 20% of components
 80% of a company’s income comes from 20% of its products
 80% of innovation comes from 20% of people
Tenix Defence
80/20 Rule
GUIDE
LINES
In design, we should:
 Identify the 20% of functions used the most and make them
easily accessed
 Not all elements are equal - avoid complex areas with little real
benefit
 Avoid estimating based on the fastest 80% of a task
Tenix Defence
Accessibility
Objects and environments should be designed to be usable by as many
people as possible

Historically this focussed on disabilities
 Advantages are applicable to wider audience
 Primary attributes:
•
•
•
•
Perceptibility – use of multiple senses (sight, sound, feel)
Operability – minimal physical exertion
Simplicity - intuitive, clear interface
Forgiveness – reduce severity of mistakes
Tenix Defence
Accessibility

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Use multiple coding methods for information:
• Colour and icons
• Text
• Tactile controls
• Audible feedback
• Minimise repetitive actions
Avoid need for sustained physical effort
Consistent and clear interface
Use progressive disclosure to only present relevant controls
Clear feedback for actions
Design to minimise consequence of mistakes, using:
• Confirmations
• Warnings
• interlocks
GUIDE
LINES
Tenix Defence
Aesthetic-Useability effect
Aesthetic designs are perceived as easier to use

A phenomenon whereby an aesthetic design
will be perceived as easier to use than a
non-aesthetic design

Nokia experienced huge demand for its
phones with clip on covers

Customers may reject a functional design due to poor aesthetics

Long term user satisfaction also driven by aesthetics
Tenix Defence
Affordance
A property in which the physical characteristics of an object influence its
function

Some objects have fundamental uses, e.g. wheels roll, handles are for
pulling, stairs for climbing
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Humans have expectations of how standard objects behave

Designs which use objects naturally tend to be
more successful, e.g. don’t use a handle on a door
which should be pushed open
Tenix Defence
Affordance
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Consider ‘expected’ behaviour of objects
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Exploit intended function of objects
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Good design will inhibit incorrect use;
GUIDE
LINES
• chairs which only stack one way
• lego blocks have a natural interlock

Computer Interface elements such as
3D buttons are clearly ‘push’ operations, sliders obviously ‘slide’
between controlled limits. These are all natural to humans.
Tenix Defence
Chunking
Combining many units of information into smaller chunks to assist human
memory and processing

Human short term memory holds 4±1 items

Lists bigger than this should be presented
as ‘Chunks’

Familiar data items (words) may exceed
this slightly, complex items (numeric values)
need smaller groups

Does not apply to lists where the operator
is scanning for a particular item; no attempt
is made to remember multiple items
Tenix Defence
Closure
A tendency to perceive a set of elements as a single pattern rather than
individual elements

Humans will recognise a constructed shape before its components
 These pictures will be initially recognised
as circles, then as groups of lines

It may not be necessary to show all information;
a simpler visual design may permit less clutter

Additionally, movement between snapshot frames
will be supplied by the viewer as seen in strip
cartoons
Tenix Defence
Colour
Colour is used to attract attention, group elements, indicate meaning and
enhance aesthetics
The human eye can process about five colours at one time – don’t
overuse colour!
 Saturated colours (pure hues) attract attention

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Desaturated colours convey information efficiently
 Use warm colours for foreground elements and cooler colours for
background
 Don’t rely on colour to convey information; a significant proportion of
the population have limited colour vision
Tenix Defence
Common fate (1)
Elements that move in the same manner are perceived to have a
relationship
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Similarity through movement is stronger than visual similarity
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Affected by:
• Direction
• Speed
• Time at which objects move
• Proximity
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Stationary objects are likely to be
associated by appearance or position
Tenix Defence
Common fate (2)
Example of common fate
Stationary: Grouped by appearance
OXOOXOXXXOO
Moving: Grouped by fate
(click)
Tenix Defence
Confirmation
Preventing unintended actions by requiring verification of actions before
they are performed
Primarily used to prevent errors known as ‘slips’
 Used to reduce likelihood of serious or dangerous actions occuring


Two types of confirmation:
• Dialog – a confirmation request is displayed after the action is
selected
– Suitable for non time critical actions,
e.g. deleting a file
– Slows operator down
• Two-step operation – an enabling action must be performed
before the critical action is selected, e.g. release safety catch
– Suited to time critical actions, e.g. firing a weapon
– Is usually more intuitive to an experienced user
Tenix Defence
Confirmation
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GUIDE
LINES
Avoid over-use of confirmations
Consider consequence of each action
Two step may remain ‘armed’ after the event, e.g. a switch cover stays
‘flipped’
Dialogs should have a clear choice of actions, OK/Cancel is rarely
suitable
‘Undo’ functionality should be considered in place of a dialog
Tenix Defence
Consistency
The usability of a system is improved when similar parts are expressed in
similar ways

Four kinds of consistency:
• Aesthetic Consistency
– Style, appearance, colour, logo
– Sets an expectation based on brand
• Functional Consistency
– Behaviour and sequence
– E.g. traffic lights all follow the same sequence
• Internal Consistency
– Items within a system work together
– E.g. Matching text fonts on a control panel
• External Consistency
– Agreement between dissimilar systems
– E.g. Open file formats
Tenix Defence
Constraint
A method of limiting the actions that can be performed on a system

Constraints are used extensively in Aerospace systems
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Can reduce errors or danger
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Improved usability through clear limits on actions
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Two types, each with subcategories:
Physical
Psychological
Paths
Symbols
Axes
Conventions
Barriers
Mappings
Tenix Defence
Constraint – Physical (1)
Paths

Convert physical force to linear/curvilinear movement
 Using channels or grooves
 Also applicable to GUIs
Tenix Defence
Constraint – Physical (2)
Axes

Convert physical force into turning motion
 Potentially infinite movement
 E.g. trackballs, radio tuning knobs
Tenix Defence
Constraint – Physical (3)
Barriers
 Absorb or deflect movement around barrier
 Deny errant actions
 E.g. Rail crossing barriers, keyed plugs, walls
Tenix Defence
Constraint – Psychological (1)
Symbols
• Communicate through text and symbols
• Warning signs, traffic arrows
Tenix Defence
Constraint – Psychological (2)
Conventions
 Learned traditions
 E.g. Red light means ‘stop’
 May be misinterpreted
Tenix Defence
Constraint – Psychological (3)
Mappings
 Proximity of objects suggests a connection
 E.g. A switch beside a power point
Tenix Defence
Control
The level of control provided by a system should be related to the
proficiency of the people using the system

Understand the target user(s) of your system

Complex controls will confuse the inexperienced, simple controls will
frustrate ‘power’ users

Systems can adapt their complexity
 E.g. windows apps hide complex
operations initially

Too much control can also introduce risk of accidental misuse
Tenix Defence
Cost-benefit
An activity will only be pursued if its benefits are equal to or greater than
the costs
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
Everything we do has a cost
• Time to read a book
• Price of a car
We only decide to do something if the perceived benefit exceeds its
cost.
 In system design we must always consider the cost AND benefit of
features
• Some features are complex and appeal to engineers, but offer little
benefit to the user. These should be avoided
• Some complex features may seem hard to implement, but offer
great benefit to the user. We should still consider these.
 Focus groups and usability tests help to determine benefit
Tenix Defence
Development Cycle
Successful products typically follow four stages of creation
 Requirements
• Controlled interactions with users
• Knowledge of analysts
 Design
• Goal is a set of specifications that meet all requirements
• Use similar systems where possible
 Development
• Ensure specifications are maintained
• Reduce variability in parts and processes
 Testing
• Focussed on requirements and user needs
• Quality of modules and their integration
Tenix Defence
Development Cycle - linear
The linear lifecycle
 Also known as waterfall
 Each phase is completed before the next is started
 Well suited to projects with fixed requirements
Requirements
Design
Development
Testing
(click)
Tenix Defence
Development Cycle - iterative
The iterative lifecycle
 Also known as rapid prototyping
 Resulting system can be closer to user needs
Requirements
Design
Development
Testing
(click)
Tenix Defence
Entry Point
A point of physical or attentional entry into a design
 Mostly associated with buildings, but also applications
 Systems which are obstructive to use are less likely to gain approval
or user support
 Three point strategy to assess a design
• Minimal barriers
– Avoid obstructing entry to program,
e.g. slow splash screens, long start up times
• Points of Prospect
– Once inside, it should be clear how to reach the information
required
• Progressive lures
– Make users want to explore deeper into the program
Tenix Defence
Errors
An action or omission of action yielding an unintended result

Most errors classed as ‘human error’ but actually stem from poor
systems
• Slips
– Action taken was not as intended
– Reduced by confirmations, affordances and constraints
• Mistakes
– Action taken was as intended but incorrect
– Can be reduced by
• Improved situation awareness, keep key indicators and
controls within one eyespan of each other
• Reduced workload from better design
Tenix Defence
Factor of safety
The use of more elements than is thought to be necessary to offset the
effects of unknown variables and prevent system failure

Most systems are deliberately over-engineered for safety or
performance
 Factor of Safety is the number of times the spec is exceeded by

FoS depends on level of ignorance of design parameters;
• Familiarity of techniques and processes
• Variability of chosen materials (steel more consistent than wood)
• Peak usage

Examples
• Steel & Concrete structures – 2x to 4x
• Wood structures – 4x to 8x
• Internet services – 3x
• Great Pyramid at Giza – 20x
Tenix Defence
Factor of safety
GUIDE
LINES

Safety also applies to meeting demand in processing systems

FoS increased by using extra material, processing power, better
materials

FoS tends to be revised downwards on subsequent systems as
process is better known; often until failure actually occurs.
• Titanic
• Space Shuttle

Rated Capacity x Fos = Design Capacity

Always use rated capacity when considering changes to system
Tenix Defence
Feedback loops
A relationship between variables in a system where the consequences of
an event feed back into the system as input, modifying future decisions

Exist in most real-world systems
 Positive Feedback
• Amplifies system output, accelerating growth or decline
• Does not seek a particular output level
• Examples are finance markets which accelerate towards crashes
 Negative Output
• Dampens output to achieve a particular state or level
• Examples: Flight control computers, temperature thermostats,
cruise controls
Tenix Defence
Fitt’s Law
The time to move to a target is a function of the distance to target and the
size of the target

E.g. Time to move a mouse pointer to an icon, or hand to a button

Two Distinct Components
• Ballistic Movement
– The large movement to get close to the control
– Depends on distance to target
– Reduced by physical barriers, e.g. edge of screen or lever end
stops
• Honing Movement
– The small movement to centre on the target
– Depends on size of target
Tenix Defence
Fitt’s Law
Useability of systems can be improved.

Place commonly used buttons near screen edges, e.g.

Context menus require little ballistic movement
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Use larger controls for frequently used items

Example – car manual shift gearboxes are fast because:
• End stops limit ballistic movement
• The target (gear) is at a physical limit, needing no honing
GUIDE
LINES
Tenix Defence
Flexibility – Usability Trade-off
As the flexibility of a system increases, it’s useability decreases

Flexibility = Complexity

For example, a swiss army knife is flexible, but none of it’s functions
are as good as a dedicated tool

Flexibility should be sought where user needs are not clear

Iterative development can be used to reduce flexibility
Tenix Defence
Forgiveness
Designs should help people avoid errors and minimise the negative
consequences when they do occur

Human error is inevitable

Forgiving Designs encourage
user confidence

Mechanisms for forgiveness
• Affordances – guide users away from slips through design
•
•
•
•
•
Reversibility – ‘Undo’, ‘Abort’ and ‘Self Destruct’
Safety nets – protection from effects of errors e.g. ejector seats
Confirmation – verification before actions
Warnings – e.g. signs, prompts, alarms of imminent danger
Help – online help or trouble shooting manuals
Tenix Defence
Garbage In – Garbage Out
The quality of system output is dependent on the quality of input

Even well trained users can enter flawed information

Effects of bad data may not surface immediately, but can be severe

Effort spent during design of system input can have big benefits
• Protect system and users
• Less user frustration

Employ affordances and constraints such as listboxes, fixed choices
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Enhance information quality with previews and confirmations
Tenix Defence
Hick’s Law
The time it takes to make a decision increases as the number of
alternatives increase

Applicable to simple decisions only, also
excludes complex menus

A driver’s reaction time to a hazard will increase
if he has the option to swerve around it

Offer the fewest choices where response time
is important

Response Time, RT = a + b.log2(n)
• a is pre-decision reaction time
• b is time per decision, typically 0.155 seconds for humans
• n is number of options
Tenix Defence
Hierarchy
Hierarchical Organisation is the simplest structure for visualising and
understanding complexity

Three approaches
• Tree
– Uses element size/position
to show relationships
• Nests
– Drawn in a Venn Diagram style
– Elements are inside others
• Stairs
– E.g. Windows explorer
Tenix Defence
Hierarchy of needs
In order for a design to be successful, it must meet people’s basic needs
before it can attempt to satisfy higher level needs
Highest Value - Allows users to create and
explore areas beyond the original design
Creativity
Proficiency
Reliability
Functionality
Level of need
Usability
High Value - Empowers users to do more
than they could before
Moderate Value - Easy to use, tolerates
mistakes
Low Value - Operation is
consistent and reliable
Little Value - Meets design
requirements, e.g. play, record
Tenix Defence
Highlighting
A technique for bringing attention to an area of text or image

Some data we present will need highlighting to users
 Keep highlighting to a maximum of 10% of items; effect reduces
 Bolding is more effective than italics or underlining; less noise

Uppercase TEXT is effective amongst lower case
 Font changes don’t stand out well

Colour is effective when used sparingly with bold colours
 Inversing elements works with text, but often obliterates icons
 Reserve blinking for highly critical data. Offer an option to stop the
blinking
Tenix Defence
Iconic representation
The use of pictorial images to improve the recognition and recall of signs
and controls

Icons can save space and highlight information, e.g. error symbols
 Four types:
• Similar Icons
– Images look like the item they represent, e.g. bend in road
• Example Icons
– Images represent things associated with the item, e.g. an
airplane for an airport
• Symbolic Icons
– An abstraction of the item represented; a lightning flash for
electricity
• Arbitrary Icons
– Memorable but no resemblance to object, e.g. radioactive
Tenix Defence
Interference Effects
A phenomenon in which mental processing is made slower and less
accurate by competing mental processes

Conflict between human mental systems will slow user responses
• Stroop interference
– An irrelevant aspect of data items contradicts the primary
meaning, e.g. RED BLUE
• Garner interference
– An irrelevant stimulus distracts attention from an item (click)
– E.g. moving symbols next to text being read
• Proactive interference
– Existing memories interfere with new information
– E.g. when learning a second language, the original will
interfere
• Retroactive interference
– Existing memories are affected by new learning
– E.g. Remembering a new phone may confuse and older one
Tenix Defence
Iteration
A process of repeating a set of operations until a specific result is achieved

Design Iteration
• Desirable process
• An initial design is continuous refined, adding more detail until
complete
• Feedback can be internal or from user groups
 Development Iteration
• Unexpected redesign necessary when building a product
• Result of poor design
• Costly and undesirable
Tenix Defence
Layering
The process of organising information into related groupings in order to
manage complexity and reinforce relationships in the information

Presentation of information is a common system function

Aim is to reduce complexity or size of information
• Two dimensional
– Primarily textual data
• Three dimensional
– Suited to geospatial data
Tenix Defence
Layering – 2D
Two dimensional layering

Linear
Beginning

Middle 1
Middle 2
End
Nonlinear
Info
Word
Synonym
Word
Synonym
Parallel; a table of values
Transport
Air
Plane
Info
Home
Info
Info
Web; complex linked data
Ground
Car
Info
Train
Hierarchical / Collapsible tree
Info
Tenix Defence
Layering – 3D
Three dimensional layering

Present a basic image, with data overlaid
 Projection may be 2D or 3D
Tenix Defence
Mental Models
People understand and interact with systems and environments based on
mental representations developed from experience

Two types of Mental Models
• System Model
– Describes how a system works
– Typically well understood by designers, not users
• Interaction Model
– Describes how users interact with the system
– Well understood by users, but not designers
– Designers must strive to understand this
– Operational Concept Document
– Focus Groups, observation of users
Tenix Defence
Modularity
A method of managing system complexity that involves dividing large
systems into multiple, smaller self-contained systems

Complex or large systems should be considered as ‘modules’

Interfaces between modules should be well defined, and ideally simple

Allows third party suppliers to have competing designsm

Many systems become more modular as they evolve
Tenix Defence
Ockham's Razor
Given a choice between equally functional designs, the simplest design
should be selected

“Everything should be made as simple as possible, but not simpler” –
Albert Einstein

Unnecessary design elements usually:
• Increase weight
• Increase Cost
• Decrease reliability
• Complicate maintenance
• Confuse users
The potato peeler
Tenix Defence
Performance Load
The greater the effort to accomplish a task, the less likely the task will be
successful

Increased load will increase errors and time to complete
 Load splits into two categories
 Cognitive Load
– Level of mental activity required
– Perception, memory, problem solving skills
– Improve by reducing visual noise, chunking and automation
• Kinematic Load
– Level of physical activity required
– Number of steps, physical force
– Improve by shortening distances, reducing steps by
automation
Tenix Defence
Performance vs preference
The designs that help people perform optimally are often not the same as
the designs that people find most desirable

Users will often favour designs they like over designs that work better

Dangerous to rely solely on user feedback at workshops

Carefully observe user performance as well as their views

BUT users may not accept an optimal design if it is too different
• E.g. Dvorak keyboard is 30% faster than qwerty, but who wants
one?
Tenix Defence
Prototyping
The use of simplified and incomplete models of a design to explore ideas,
elaborate requirements, refine specifications and test functionality

Three basic kinds
• Concept prototyping
– Concept sketches, storyboards
– Facilitate user workshops
• Throwaway prototyping
– Representative models
– Discarded after use
– Quick to produce
• Evolutionary prototyping
– Prototype will be refined in multiple steps
– Can become final product, e.g. computer GUI
– Risk of refining when radical redesign needed
Tenix Defence
Redundancy
Use of more elements than necessary to maintain the performance of a
system in the event of failure of one or more of the elements

Diverse Redundancy
• Multiple elements of diverse types
• E.g. Trains may have electric, hydraulic and pneumatic brakes

Homogenous Redundancy
• Multiple elements of a similar type
• E.g. strands in a rope
 Active Redundancy
• Elements are all in use continuously
• E.g. Pillars supporting a roof

Passive Redundancy
• Elements are swapped in when failure happens
• E.g. Spare tyre on a car
Tenix Defence
Scaling Fallacy
A tendency to assume that a system that works at one scale will also work
at a smaller or larger scale

Affects prototypes and performance testing
 Wrong to assume that all physical effects scale in the same way
 Some properties scale linearly, whilst others may be exponential

E.g. an ant can carry 50x its own weight, but not if scaled up to human
size
 Complex interactions occur when the number of items increases
 Computer systems can be affected in a similar way
• Doubling processing power may not double speed
• Doubling users may not halve throughput
• Network performance degrades quickly near its limits
Tenix Defence
Signal to Noise Ratio
The ratio of relevant to irrelevant information in a display

Highest possible signal-to-noise ratio is desirable

Signal - relevant data – what we are trying to communicate

Noise – introduced to organise or convey the data, e.g. table borders,
shading, gratuitious clip art
Tenix Defence
Structural Forms
There are three ways to organise materials to support a load or to contain
and protect something
 Mass Structures
• Solid structures which rely on mass
• E.g. dams, mountains, pyramids
• Tend to strongly resist failure

Frame Structures
• Internal frame, usually made from triangular sections
• E.g. Eiffel Tower, houses

Shell Structures
• A thin material that contains a volume
• Strength comes from ability to spread loads
across the surface
• E.g. eggs, bottles, steam boilers
Tenix Defence
Uncertainty Principle
The act of measuring certain sensitive variables in a system can alter them,
and confound the accuracy of the measurement
Based on Heisenberg’s uncertainty principle (atomic physics)
 Two aspects to a measurement
• Sensitivity

– Ease with which a property being measured can be altered
• Invasiveness
– Amount of interference caused by the measurement
 Examples
• Performance measurement of a computer uses resources
• Voltage measurement draws current & reduces the voltage
• Students adapt to examination techniques to score better

Strive for low invasiveness; sensitivity is predetermined
Tenix Defence
Uniform connectedness
Elements that are connected by uniform visual properties are perceived to
be more related than elements that are not connected

Elements close to each with similar appearance will automatically
group

Human perception will override this if physical connection is shown

Connection lines and shaded areas can group elements
Tenix Defence
Visibility
The usability of a system is improved when its status and methods of use
are clearly exposed

Systems are more usable when they clearly indicate:
• Their status
• The possible actions that can be performed
• The consequences of those actions

E.g. a red light next to a switch marked ‘Power’

Progressive disclosure on a GUI is an effective tool
Tenix Defence
Weakest Link
The deliberate use of a weak element that will fail in order to protect other
elements in the system from damage

Examples
• Fuse in a circuit
• Crumple zone in a car

Two types of protection through a weak link
• Passive
– The breakage of the element protects, i.e. a fuse
• Active
– Breakage of the element triggers a response, i.e. a sprinkler
system trigger by breakage of a glass bulb