Design Principles

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Design Principles
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Design Principles - Overview

• Apply at multiple levels of design
• Become obvious to user of poorly-designed Uis
• Are easy to ignore
• Are neither complete nor orthogonal
• Have underpinnings in psychology or experience or
  common sense

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UI Design Principles

• Categories
• 1. Learnability
• Support for learning for users of all levels
• 2. Flexibility
• Support for multiple ways of doing tasks
• 3. Robustness
• Support for recovery
• Always think about exceptions, suitability

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Many Sets of Design Principles

• Shneiderman, Designing the User Interface
• Dix, Finlay, Abowd, Beale, Human-Computer
  Interaction
• Foley et al, Computer Graphics Principles and
  Practice
• And many more

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1. Learnability Principles

• Ease with which new users can begin effective
  interaction and achieve maximal performance
• Predictability
• Synthesizability
• Familiarity Metaphor
• Generalizability
• Consistency

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2. Flexibility Principles

• Multiplicity of ways that users and system
  exchange information
• Dialog Initiative
• Multithreading
• Task migratability
• Substitutivity
• Customizability

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3. Robustness Principles

• Supporting user in determining successful
  achievement and assessment of goals
• Observability
• Do not set the user up (for a fall, ie, an error)
• Recoverability
• Responsiveness
• Task Conformance

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Good Design (our goal!)

• Every designer wants to build a high-quality
  interactive system that is admired by colleagues,
  celebrated by users, circulated widely, and
  imitated frequently. (Shneiderman, 1992, p.7)
• and anything goes!

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Why Principles Guidelines?

• Because, well, not everything goes
• Intended to prevent many bad designs before they
  begin, or evaluate existing designs on a
  scientific basis
• Guidelines based on previous designs,
  experimental findings
• Rules can all be broken (but usually in order
  to satisfy another principle)

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Concepts, Principles, Guidelines

• No cookbooks
• No simple, universal checklists
• There are many concepts, principles, and
  guidelines
• Understand the higher level principles that apply
  across situations, display types, etc.
• Implement the standards and guidelines
• a few details

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Levels of Consideration

• Meta-display level
• Apply to the whole system, across media across
  displays
• Focus on this in Basic Layout Stage
• Display Layout
• Apply to groups of elements in a display
• Focus on this in Prototyping and Redesign
• Element level
• Details about specific parts of a display
• Colors, sound attributes, symbols

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UI Design Principles

• Categories
• Learnability
• Support for learning for users of all levels
• Flexibility
• Support for multiple ways of doing tasks
• Robustness
• Support for recovery
• Always think about exceptions, suitability

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1. Learnability Principles

• Ease with which new users can begin effective
  interaction and achieve maximal performance
• Predictability
• Synthesizability
• Familiarity
• Generalizability
• Consistency

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1.1 Predictability

• I think that this action will do.
• Mental model can help
• Operation visibilityCan see avail actions
• e.g. menus vs. command shell
• grayed menu items

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Mental Models - Aid Predictability

• Mental models are not always right
• Two Classes
• Functional model
• Stimulus - response
• Press the accelerator once, then turn the key
• Structural model
• Deeper sense of why it happens, not just what
  happens
• Press the accelerator to engage the automatic
  choke on a carburetor

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Another example - directions...

• Functional model
• Give turn-by-turn directions
• East on Ponce, turn left just after Harrys in a
  Hurry, then go to the third set of lights

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Another example - directions...

• Structural model
• Provide higher-level understanding
• Using map, go to Virginia Highland

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1.2 Synthesizability

• Support for user in assessing the effect of past
  operations on current system state
• Moving a file in UNIX shell vs. Mac/Windows
• Is same feedback needed for all users, all apps?

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1.3 Familiarity

• Does UI task leverage existing real-world or
  domain knowledge?
• Really relevant to first impressions
• Use of metaphors
• Potential pitfalls
• Are there limitations on familiarity?

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Metaphors at the UI - What

• Metaphor - Application of name or descriptive
  term to another object which is not literally
  applicable
• Use Natural transfer - apply existing knowledge
  to new, abstract tasks
• Problem May introduce incorrect mental model
• Macintosh -dragging CD to trash can to eject

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Metaphor Creation - Prepare

• Prepare
• What functions are needed
• What are users problems?

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Metaphor Creation - Generate

• Generate
• Use metaphor that matches users conceptual tasks
• Given choice, choose metaphor closest to way
  system really works
• Ensure emotional tone is appropriate to users

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Metaphor Creation - Evaluate

• Evaluate
• Ask users how they would do common tasks
• Learn what is confusing and what is helpful
• Evolve
• Mental Models

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1.4 Generalizability

• Can knowledge of one system/UI be extended to
  other similar ones?
• Example cut paste in different applications
• Does knowledge of one aspect of a UI apply to
  rest of the UI?
• Aid UI Developers guidelines

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1.5 Consistency

• Likeness in behavior between similar
  tasks/operations/situations/terminology
• Interaction sequences
• Quicken on Mac Option-P prints check, not
  current document
• Output
• Dialogue box always has a close button
• Screen layout
• Menu items always in same place - leverage
  muscle memory
• Is this always desirable for all systems, all
  users?

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Consistency (contd)

• Avoid special cases and special rules
• Supports generalization by user, avoids
  frustration
• For command line systems - consistent syntax
• Find consistency between commands, unify them -
  as in Unix pipes for file I/O and for process
  inter-communications

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(In)Consistency Example

• For a graphics program that uses a CSO
  (Currently-Selected Object)
• Create a new primitive, it becomes the CSO
• Duplicate a primitive, the old primitive remains
  as CSO

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(In)Consistency Example - Macintosh

• Drag a file icon to
• Folder on same physical disk
• Folder on another physical disk
• Different disk
• Trash can

• Result
• File is moved to folder
• File is copied there
• File is copied there
• File is discarded

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FSMs can Reveal Inconsistencies
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2. Flexibility Principles

• Multiplicity of ways that users and system
  exchange information
• Dialog Initiative
• Multithreading
• Task migratability
• Substitutivity
• Customizability

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2.1 Dialog Initiative

• Not hampering the user by placing constraints on
  how dialog is done
• User pre-emptive
• User initiates actions
• More flexible, generally more desirable
• System pre-emptive
• System does all prompts, user responds
• Sometimes necessary

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2.2 Multithreading

• Allowing user to perform more than one task at a
  time
• Two types
• Concurrent
• Input goes to multiple tasks simultaneously
• Interleaved
• Many tasks, but input goes to one at a time

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2.3 Task Migratability

• Ability to move performance of task to the entity
  (user or system) that can do it better
• Spell-checking, safety controls in plant
• For what kinds of tasks should the user be in
  control?

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2.4 Substitutivity

• Flexibility in details of operations
• Allow user to choose suitable interaction methods
• Allow different ways to
• perform actions, specify data, configure
• Allow different ways of presenting output
• to suit task user

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2.4 Substitutivity

• Drafting page layout systems
• Indicate positions with cursor
• or
• By typing in coordinates
• Give temperature via slider or by typing
• Examples of spatial vs. linguistic specification

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2.5 Customizability

• Ability of user to modify interface
• By user - adaptability
• Is this a good thing?
• By system - adaptivity
• Is this a good thing?

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3. Robustness Principles

• Supporting user in determining successful
  achievement and assessment of goals
• Observability
• Recoverability
• Responsiveness
• Task Conformance

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3.1 Observability

• Can user determine internal state of system from
  what she perceives?
• Browsability
• Explore current state (without changing it)
• Reduces memory load
• But dont overwhelm user with information either
• Reachability
• Navigate through observable states
• Persistence
• How long does observable state persist?
• Observability also aids learnability

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3.1 Observability - Role of Feedback

• Feedback helps create observability
• Feedback taxonomy (generally dont need all of
  these)
• I understand what you have asked me to do
• I am doing what you have asked me to do
• And it will take me this much longer
• Song and dance routine to distract user (busy
  interval as opposed to idle interval)
• And here are some intermediate results to keep
  you happy until I am done
• All done, whats next?

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3.1 Observability - Forest Trees
Represents overall drawing
Work area, showing part of a larger drawing
Represents portion of drawing seen in work area
Menus, feedback, etc.
Overall display area
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3.1 Observability Acrobat Reader

• Acrobat Reader with ToC to give context
• Forest is the bookmarks, tree is the single page

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3.1 Observability - Scroll Bar

• Scroll bar size indicates in view - but does
  not indicate absolute sizes.
• Can add other info, such as
• Page 5 of 12

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3.1 Observability - feedback placement

• Where the eyes are
• Cursor shape
• In Newshole
• Thumbs down problem
• Buddha to encourage patience
• Audio output avoids this issue

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3.1 Observability - Memory Load

• Use as a tool to decrease user memory load
• Also to avoid mis-steps
• Gray-out disabled menu items
• Indicate type of input (alpha, numbers) expected

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3.2 Do Not Set the User Up

• Make it hard for the user to make errors
• Instead of allowing them to make error and then
  saying tsk, tsk
• Gray out disabled menu items
• Ask for confirmation of major actions

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3.2 Do Not Set the User Up

• For command language applications, create
  matching end token when begin token is typed
• ( -gt ) lttitlegt -gt lt/titlegt
• begin -gt end
• repeat -gt until
• / -gt /

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3.2 Do Not Set the User Up

• Dont let the user do something that will lead to
  an error message

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3.2 Recoverability

• Ability to take corrective action upon
  recognizing error
• Forward recovery
• Ability to fix when we cant undo
• Backward recovery
• Undo previous error(s)
• Abort operation underway
• Only makes sense if is a slow operation
• Encourages experimentation (hence learnability)
  by reducing cost of making mistakes

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3.3 Responsiveness

• Users perception of rate of communication with
  system (not always right)
• Response time
• Time for system to respond in some way to user
  action(s)
• Response OK if matches user expectations
• Once user enjoys fast response, is hard to go
  back to slower response
• Dial-up versus DSL or Cable Modem

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3.3 Responsiveness

• Response to motor actions
• Keyboarding, mouse movement - less than 100 msec.
• Rich Human Factors literature on this
• Consistency is important - experimental result
• Users preferred longer but more consistent
  response time
• Times that differed 10 to 20 were seen as same
• Sometimes argued that too fast is not good
• Makes user feel like they need to do something
  quickly to keep up with comptuer?

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3.4 Task Conformance

• Does system support all tasks user wishes to
  perform in expected ways?
• Task completeness
• Can system do all tasks of interest?
• Task adequacy
• Can user understand how to do tasks?
• Does it allow user to define new tasks?
• Extensibility

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Using the Principles

• In doing design and implementation of your
  project, revisit this list
• Assess your design against these usability
  principles

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Good Design (reminder!)

• Every designer wants to build a high-quality
  interactive system that is admired by colleagues,
  celebrated by users, circulated widely, and
  imitated frequently. (Shneiderman, 1992, p.7)
• and anything goes!

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The Good
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The Good
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The Bad
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The Bad
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The Bad
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The Ugly
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The (really) Ugly
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But What Makes it Good?

• Functionality
• Speed efficiency
• Reliability, security, data integrity
• Standardization, consistency
• USABILITY !

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A Philosophy

• The human user of any system is the focus of the
  design process. Planning and implementation is
  done with the user in mind, and the system is
  made to fit the user, not the other way around.

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Good Design Means

• Systems are built for humans must be designed
  for the user
• Recognize individual differences appreciate
  design implications of these human factors
• Recognize the design of things, procedures, etc.,
  influences human behavior and well-being
• Emphasize empirical data evaluation
• Rely on the scientific method
• Things, procedures, environments, and people do
  not exist in isolation

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Good Design is NOT

• NOT just applying checklists and guidelines
• These can help, but UCD is a whole philosophy
• NOT using oneself as the model user
• Know your real users recognize variation in
  humans
• NOT just common sense
• Knowing how to design a fire alarm so it will be
  heard over background noise is not something we
  all know.
• The HF specialist knows where or how to get the
  information needed to answer design questions