Design rules

1
Design rules

• Dr. Yan Liu
• Department of Biomedical, Industrial and Human
  Factors Engineering
• Wright State University

2
Introduction

• Design Rules
• Rules that a designer can follow in order to
  increase the usability of the eventual products
• Can be supported by psychological, cognitive,
  ergonomic, sociological, economic or
  computational theories which may or may not have
  roots in empirical evidence
• Authority
• Whether the rule must be followed in design or it
  is only suggested
• Generality
• Whether the rule can be applied to many design
  situations or it is focused on a more limited
  application situation

3
Introduction

• Types of Design Rules
• Principles
• Derived from knowledge of the psychological,
  computational and sociological aspects of the
  problem domains
• Largely independent of the technology and
  dependent to a much greater extent on a deeper
  understanding of the human element in the
  interaction
• Abstract design rules, with low authority and
  high generality
• Guidelines
• Less abstract than principles and often more
  technology oriented
• Still general important for a designer to know
  what theoretical evidence there is to support
  them
• Relatively higher authority than principles
• Standards
• Specific design rules less important for a
  designer to know the underlying theory
• High authority and limited application

4
Introduction

• Issues
• Conflicts between design rules
• The theory underlying the separate design rules
  can help the designer understand the trade-off
  for the design
• The more general a design rule is, the greater
  the likelihood that it will conflict with other
  rules and the greater the need for the designer
  to understand the theory behind it
• When to use design rules within the design
  process
• Design rules would be most effective if they
  could be adopted in the earliest stages of the
  life cycle
• Requirement specification
• Some specific design rules are applicable only at
  later stages of the design life cycle
• e.g. Design rules on color vs. monochrome screens
  or two- versus three-button mouse depends on the
  particular hardware platform

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Principles to Support Usability

• Categories
• Learnability
• The ease with which new users can begin effective
  interaction and achieve maximal performance
• Flexibility
• The multiplicity of ways in which the user and
  system exchange information
• Robustness
• The level of support provided to the user in
  determining successful achievement and assessment
  of goals

6
Learnability

• Predictability
• The degree to which users knowledge of the
  interaction history is sufficient to determine
  the result of his/her future interaction with it
• Degrees to which predictability can be satisfied
• The knowledge is restricted to the presently
  perceivable information, so that the user does
  not need to remember anything other than what is
  currently observable
• The knowledge requirement is so high that the
  user is forced to remember what every previous
  keystroke was and what every previous screen
  display contained (and even the order of each) in
  order to determine the consequences of the next
  input action
• Operation visibility
• How the user is shown the availability of
  operations that can be performed next
• If an operation can be performed, then there
  should be some perceivable indication of this to
  the user
• The user should understand from the interface if
  an operation he/she might like to invoke cannot
  be performed
• Supports the superiority in humans of recognition
  over recall

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Learnability

• Synthesizability
• The ability of the user to assess the effect of
  past operations on the current state
• Honesty of the system
• The ability of the user interface to provide an
  observable and informative account of any change
  in the internal state of the system
• In the best circumstance, this notification
  should come immediately, requiring no further
  interaction by the user (immediate honesty)
• e.g. In a Windows system, to move a file from one
  directory to another directory, the user drags
  the visual icon of the file from the original
  directory to the destination directory where it
  remains visible
• At the very least, the notification should appear
  eventually, after explicit user directives to
  make the change observable (eventual honesty)
• e.g. In a command language system, the user would
  have to remember the destination directory and
  ask to see the contents of the directory in order
  to verify that the file has been moved
  successfully

8
Learnability

• Familiarity
• The correlation between the users prior
  knowledge and the knowledge required for using
  the new system
• e.g. When the word processor was originally
  introduced, the analogy between the word
  processor and a typewriter was intended to make
  the new technology more immediately accessible to
  those who had little experience with the former
  but a lot of experience with the latter
• Affordance
• The appearance of an object suggests how it can
  be manipulated
• e.g. The shape of a door handle suggests how it
  should be manipulated to open a door a key on a
  keyboard suggests that it can be pushed
• Effective use of the affordances that exist for
  interface objects can enhance the familiarity of
  the interactive system

9
Learnability

• Generalizability
• The ability of the user to extend his/her
  specific interaction knowledge to situations that
  are similar but previously unencountered
• Can occur within a single application or across a
  variety of applications
• e.g. In a graphical drawing package that draws a
  circle as a constrained form of ellipse, the user
  can generalize that a square can be drawn as a
  constrained rectangle
• One of main advantages of standards is that they
  increase generalizability across different
  applications within the same environment

10
Learnability

• Consistency
• The likeness in behavior arising from similar
  situations or similar task objectives
• Must be applied relative to something
• e.g. consistency in command naming, consistency
  in icon layout
• Many other principles can be considered as
  instances of consistency
• Familiarity can be considered as consistency with
  respect to past experiences
• Generalizability can be considered as consistency
  with respect to experience with similar
  applications on the same platform

11
Flexibility

• Dialog Initiative
• System pre-emptive
• The system initiates all the dialogs and the user
  simply responds to requests for information
  allows little flexibility
• e.g. The search dialog box at the WSU library
  website only allows users to input the search
  criteria in the form required by the system
• Usually undesirable but may be required in some
  situations
• e.g. For safety reasons, it may be necessary to
  prohibit the user from the freedom to do
  potentially serious damages
• User pre-emptive
• The user is entirely free to initiate any action
  towards the system allows the maximum
  flexibility
• A completely user pre-emptive is not necessary a
  desirable situation, as it increases the
  likelihood that the user will lose track of the
  tasks that have been initiated and not yet
  completed

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Flexibility

• Multi-Modality
• Provides the user with multiple modes of
  interfacing with a system beyond the traditional
  keyboard and mouse input/output
• Types
• A single input/output expression can be formed by
  separate alternative modalities
• e.g. To open a new window, the user can choose to
  click the new window icon or say opening a new
  window
• A single expression can be formed by a mixing of
  different modalities
• e.g. Error warnings usually contain a textual
  message accompanied by an audible beep

13
Flexibility

• Task Migratability
• The transfer of control for execution of tasks
  between system and user
• It should be possible for the user or system to
  pass the control of a task over to the other or
  promote the task from a completely internalized
  one to a shared and cooperative venture
• e.g. On the flight deck of an aircraft, there are
  so many control tasks that must be performed that
  a pilot would be overwhelmed if he had to perform
  them all. Therefore, mundane control of the
  aircrafts position within its flight envelope is
  greatly automated. However, in the event of an
  emergency, it must be possible to transfer flying
  controls easily and seamlessly from the system to
  the pilot

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Flexibility

• Substitutivity
• Equivalent values can be substituted for each
  other
• e.g. Allow users to input margin for a letter in
  inches or centimeters
• Representation multiplicity
• e.g. The temperature of a physical object over a
  period of time can be presented as a digital
  thermometer if the actual numerical value is
  important or as a graph if it is only important
  to notice trends. It might even be desirable to
  make these representations simultaneously
  available to the user

15
Flexibility

• Customizability
• Modifiability of the user interface by the user
  or the system
• Adaptability
• The users ability to adjust the form of input
  and output
• e.g. The user can adjust the position of the
  icons on the screen, change the font of texts,
  etc.
• Adaptivity
• Automatic customization of the user interface by
  the system
• Decision for adaptation can be based on user
  expertise or observed repetition of certain task
  sequences
• e.g. A system can be trained to recognize the
  behavior of an expert or novice and accordingly
  adjust its dialog control or help system
  automatically to match the needs of the current
  user
• The users role is more implicit in an adaptive
  interface than in an adaptable interface

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Robustness

• Covers features that support the successful
  achievement and assessment of the goals
• Observability
• Allows the user to evaluate the internal state of
  the system by means of its perceivable
  representation at the interface
• Browsability
• Allows the user to explore the current internal
  state of the system via the limited view provided
  at the interface
• e.g. Pressing Ctrl Alt Del keys brings
  up the Windows Task Manager window which shows
  the applications currently running in the
  computer
• Availability of defaults
• Assists the user by passive recall
• e.g. Providing the user his login ID when he
  needs to access his account
• Reduces the number of physical actions necessary
  for inputting

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Robustness

• Observability (Cont.)
• Reachability
• The possibility of navigation through the
  observable system states
• Reachability in an interactive system affects the
  recoverability of the system
• Persistence
• Deals with the duration of the effect of a
  communication act and the ability of the user to
  make use of that effect
• The effect of vocal communication does not
  persist except in the memory of the receiver
• e.g. If you are informed of a new email message
  by a beep at your terminal, you may know at that
  moment and for a short while later you have
  received a message. But if you do not attend to
  that message immediately, you may forget about it
• Visual communication can remain as an object
  which the user can subsequently manipulate long
  after the act of presentation
• e.g. If some persistent visual information (such
  as a flag going up on your email box) informs you
  of the incoming message, then that will serve as
  a reminder that an unread message remains long
  after its initial receipt

18
Robustness

• Recoverability
• The ability to reach a desired goal after
  recognition of some error in a previous
  interaction
• Forward error recovery
• Involves the acceptance of the current state and
  negotiation from that state towards the desired
  state
• May be the only possibility for recovery if the
  effects of interaction are not revocable
• e.g. In a text editor, after you save the changes
  you have made on a text, you cannot undo the
  effect of saving
• Backward error recovery
• An attempt to undo the effects of previous
  interaction in order to return to a prior state
  before proceeding
• e.g. In a text editor, a mistyped keystroke may
  wipe out a large section of text which you would
  want to retrieve by an equally simple undo button

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Robustness

• Recoverability (Cont.)
• Recoverability is linked to reachability
• The user should be able to get to a desired state
  from some other undesired state
• Commensurate effort
• If it is difficult to undo a given effect on the
  state, then it should have been difficult to do
  in the first place easily undone actions should
  be easily doable
• e.g. If it is difficult to recover files which
  have been deleted in an operating system, then it
  should at least require some effort to remove
  them in the first place

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Robustness

• Responsiveness
• Measures the rate of communication between the
  system and the user
• Response time
• The duration of time needed by the system to
  express state changes to the user
• Short durations and instantaneous response time
  are usually desirable
• In situations when an instantaneous response
  cannot be obtained, there must be some indication
  to the user that the system has received the
  request for action and is working on a response
• Response time stability
• The invariance of the duration for identical or
  similar computational resources
• e.g. Pull-down menus are expected to pop up
  instantaneously as soon as a mouse button is
  pressed
• Variation in response time will impede the users
  anticipation of system response

21
Guidelines

• More specific than Principles
• The more abstract a guideline, the more it
  resembles a principle
• The more specific a guideline, the more suited it
  is to detailed design
• Published Guidelines for Interactive System
  Design (Guidelines for User Interface Design)
• Guidelines for Designing User Interface Software
  (Smith Mosier, 1986 http//www.hcibib.org/sam/)
  
• A very comprehensive catalog of guidelines
• Contains six basic categories data entry, data
  display, sequence control, user guidance, data
  transmission, and data protection

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Guidelines

• Published Guidelines for Interactive System
  Design (Cont.)
• Principles and Guidelines in Software User
  Interface Design (Mayhew, 1997)
• Another comprehensive catalog of general
  guidelines
• One of the best sources for the experimental
  results which back the specific guidelines
• Style guides for graphic user interface (GUI)
  systems
• Suggestions on conventions for programming in
  that environment
• Aim to promote consistency within and between
  applications on the same computer platform
• e.g. Web Style Guide (2nd Edition, Lynch
  Horton, 2004), Graphical User Interface Style
  Guide for Mobile Communication (Abramovici
  Klubmann, 1994)

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Standards

• Purpose
• Standards for interactive system design are
  usually set by national or international bodies
  to ensure compliance with a set of design rules
  by a large community
• Compare Standards for Hardware and Software
• Underlying theory
• Standards for hardware are based on studies of
  physiology or ergonomics the results are
  relatively well known, stable and readily
  adaptable to design of the hardware
• Standards for software are based on theories from
  psychology and cognitive science they are less
  well formed, still evolving and not very easy to
  interpret in the language of software design
• Change pattern
• Requirements changes for hardware are less
  frequent than those for software
• Since standards are also relatively stable, they
  are more suitable for hardware than for software

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Standards

• ISO (International Organization for
  Standardization) Standards for HCI and Usability
  (see the article which can be downloaded on the
  course website)
• The use of product
• Effectiveness, efficiency, and satisfaction in a
  particular context of use
• The user interface and interaction
• The process used to develop the product
• The capability of an organization to apply
  user-centered design

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Golden Rules and Heuristics

• Heuristics
• Rules of thumb or educated guesses that reduce
  or limit the search for solutions in domains that
  are difficult and poorly understood
• May not be applicable to every situation, but
  provide a useful checklist or summary of the
  essence of design advice
• Any designer following these simple rules will
  produce a better system than one who ignores them
• The most popular ones are Nielsens ten
  heuristics for usability evaluation,
  Shneidermans eight golden rules of interface
  design, and Normans seven principles for
  transforming difficult tasks into simple ones

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Shneidermans Eight Golden Rules

• Overview
• Designing the User Interface (Shneiderman,2004)
• Provide a convenient and succinct summary of the
  key principles of interface design
• Rule 1 Strive for Consistency
• Consistent sequences of actions should be
  required in similar situations identical
  terminology should be used in prompts, menus, and
  help screens and consistent commands should be
  employed throughout
• Rule 2 Enable Frequent Users to Use Shortcuts to
  Perform Regular, Familiar Actions More Quickly
• As the frequency of use increases, so do the
  user's desires to reduce the number of
  interactions and to increase the pace of
  interaction. Abbreviations, function keys, hidden
  commands, and macro facilities are very helpful
  to an expert user

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Shneidermans Eight Golden Rules

• Rule 3 Offer Informative Feedback
• For every operator action, there should be some
  system feedback. For frequent and minor actions,
  the response can be modest, while for infrequent
  and major actions, the response should be more
  substantial
• Rule 4 Design Dialogs to Yield Closure
• Sequences of actions should be organized into
  groups with a beginning, middle, and end. The
  informative feedback at the completion of a group
  of actions gives the operators the satisfaction
  of accomplishment, a sense of relief, the signal
  to drop contingency plans and options from their
  minds, and an indication that the way is clear to
  prepare for the next group of actions
• Rule 5 Offer Simple Error Handling
• As much as possible, design the system so the
  user cannot make a serious error. If an error is
  made, the system should be able to detect the
  error and offer simple, comprehensible mechanisms
  for handling the error

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Shneidermans Eight Golden Rules

• Rule 6 Permit Easy Reversal of Actions
• This feature relieves anxiety, since the user
  knows that errors can be undone it thus
  encourages exploration of unfamiliar options. The
  units of reversibility may be a single action, a
  data entry, or a complete group of actions
• Rule 7 Support Internal Locus of Control
• Experienced operators strongly desire the sense
  that they are in charge of the system and that
  the system responds to their actions. Design the
  system to make users the initiators of actions
  rather than the responders
• Rule 8 Reduce Short-Term Memory Load by Keeping
  Displays Simple, Consolidating Multiple Page
  Displays and Providing Time for Learning Action
  Sequences
• The limitation of human information processing in
  short-term memory requires that displays be kept
  simple, multiple page displays be consolidated,
  window-motion frequency be reduced, and
  sufficient training time be allotted for codes,
  mnemonics, and sequences of actions

29
Normans Seven Principles

• Overview
• The Design of Everyday Things (Norman, 1998)
• Provide a useful summary of Normans
  user-centered design philosophy
• Principle 1 Use Both Knowledge in the World and
  Knowledge in the Head
• Three conceptual models
• Design model conceptualization that the designer
  has in mind
• Users model what the user develops to explain
  the operations of the system
• System image its physical appearance, its
  operation, the way it responds, and the manual
  and instructions that accompany it
• Ideally, the users model and the design model
  are equivalent. However, the user and designer
  communicate only through the system itself. Thus
  the system image is critical the designer must
  ensure that everything about the product is
  consistent with and exemplifies the operation of
  the proper conceptual model

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Normans Seven Principles

• Principle 2 Simplify the Structure of Tasks
• Provide mental aids to help the user keep track
  of stages in a more complex task
• Use technology to make visible what would
  otherwise be invisible, thus providing feedback
  and the ability to keep control
• Automate the task or part of it, as long as this
  does not detract from the users experience
• Change the nature of the task so that is becomes
  something more simple
• Principle 3 Make Things Visible Bridge the
  Gulfs of Execution and Evaluation
• Make things visible on the execution side of an
  action so people know what is possible and how
  actions should be done make things visible on
  the evaluation side so that people can tell the
  effects of their actions

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Normans Seven Principles

• Principle 4 Get the Mappings Right
• Exploit natural mappings, make sure the user can
  determine the relationships
• Between intentions and possible actions
• Between actions and their effect on the system
• Between actual system state and what is
  perceivable by sight, sound or feel
• Between the perceived system state and the needs,
  intentions, and expectations of the user
• Principle 5 Exploit the Power of Constraints,
  Both Natural and Artificial
• Use constraints so that the user feels there is
  only one possible thing to do (the right thing!)
• Principle 6 Design for Errors
• To err is human, so anticipate the errors the
  user could make and design recovery into the
  system

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Normans Seven Principles

• Principle 7 When All Else Fails, Standardize
• If there are no natural mappings then arbitrary
  mappings should be standardized so that users
  only have to learn them once
• e.g. A number of aspects of car driving had to be
  standardized, such as side of the road to drive
  on, side of the car the driver sits on, positions
  of essential components such as steering wheel,
  clutch, brakes, accelerator, etc.