chapter six

Design rules and Implementation Support

Design Rule Chp 6

 Contents
 Universal Design
 Universal Design Principles
 Design Rules
 Principles of usability
 Standards and guidelines
 Design patterns
 Universal design
 Universal design is the process of designing products so that they
can be used by as many people as possible in as many situations as
possible

 People have different

 abilities and weaknesses; they come from different backgrounds and
cultures;
 interests, viewpoints and experiences; they are different ages and
sizes.
 All of these things have an impact on
 the way in which an individual will use a particular computing
application and,
 whether or not they can use it at all.
Universal Design Principles
 In reality, we may not be able to design everything to be accessible to
everyone
 but we can work toward the aim of universal design and try to provide an
equivalent experience.
 The seven general principles of universal design may help us in this
regard
 Equitable use - No user is excluded or stigmatized
 Flexibility in use - allows for a range of ability and preference
 Simple and intuitive to use - should not be unnecessarily complex
 Perceptible information - different forms & support the range of devices
 Tolerance for error – minimizing the damage caused by mistakes
 Low physical effort - minimizing physical effort and fatigue
 Size and space for approach and use - used regardless of body size, posture
or mobility
 Design Rules
 Designing for maximum usability is the goal of
interactive systems design.
 Design rules
 provide designers with the ability to determine the usability
consequences of their design decisions.
 are rules a designer can follow in order to increase the
usability of the eventual software product
 Three types of design rules
 Principles - abstract design rules, low authority and high
generality
 Standards - specific design rules, high authority but limited
application
 Guidelines - lower authority, more general application
 Principles to Support Usability
 Three main categories of principles
 Learnability
 theease with which new users can begin effective
interaction and achieve maximal performance

 Flexibility
 themultiplicity of ways the user and system exchange
information

 Robustness
 the
level of support provided to the user in determining
successful achievement and assessment of goal-directed
behaviour.
 Principles of Learnability
 Predictability
 determining effect of future actions based on past
interaction history i.e. the user’s ability to determine the
effect of future interactions
 assumes that the user has some mental model of how the
system behaves
 Examples
 0,3, 6, …. Next number?
 When I type the title of my task, my digital diary suggests
location of the task on the basis of past task history
 Principles of Learnability
Synthesizability


 is the ability of the user to assess the effect of past

operations on the current state.
 E.g. When an operation changes some aspect of the internal
state, the change is should be seen by the user.
 Principles of Learnability…
 Familiarity
 how prior knowledge applies to new system
 E.g. analogy between the word processor and a typewriter
 Generalizability
 Extending specific interaction knowledge to new situations
 E.g. draw a circle as a constrained form of ellipse  square
can be drawn as a constrained rectangle
 Consistency
 likeness in input/output behaviour arising from similar
situations or task objectives
 E.g. consistency in command naming, or consistency in
command/argument invocation
 Principles of flexibility
 Dialogue initiative
 Freedom from system imposed constraints on input dialogue
 System vs. User pre-emptiveness.
 Multithreading
 ability of system to support user interaction for more than
one task at a time
 concurrent vs. interleaving; multimodality
 Task migratability
 passing responsibility for task execution between user and
system
 E.g. Spell-checking
 proper names checked by the user others by the system
 Principles of flexibility…
 Substitutivity
 allowing equivalent values of input and output to be
substituted for each other
 E.g. Enter an input for length in

 meter(1m, 1 meter, 1),

 Centimetre (100cm, 100centimeter, 100) or

 formula that produces a number

 Customizability
 modifiability of the user interface by user (adaptability) or
system (adaptively).
 Principles of robustness
 Observability
 ability of user to evaluate the internal state of the system from
its perceivable representation

 Recoverability
 ability of user to take corrective action once an error has been
recognized
 reachability; forward/backward recovery; commensurate effort
 Principles of robustness …
 Responsiveness
 measures the rate of communication between the system and
the user.
 Response time is generally defined as the duration of time

needed by the system to express state changes to the user.

 Task conformance
 degree to which system services support all of the user's tasks
 task completeness - the coverage issue

 task adequacy - the user’s understanding of the tasks

 Standards
 Set by national(BSI) or international (ISO) bodies to ensure
compliance with a set of design rules by a large community standards
 Standards can apply specifically to either the hardware or the
software used to build the interactive system.

 Hardware standards more common than software high authority and

low level of detail

 ISO 9241 defines usability as

 Effectiveness - accuracy and completeness
 Efficiency - the resources (time, memory) expended
 Satisfaction - comfort and acceptability
Standards…
 Guidelines
 More suggestive and general
 Many textbooks and reports full of guidelines
 Abstract guidelines (principles) applicable during early
life cycle activities
 Detailed guidelines (style guides) applicable during later
life cycle activities
 Example
 Shneiderman’s 8 Golden Rules
 Norman’s 7 Principles [Home reading Assignment]
 Nielsen’s 10 Heuristics (study on your own)
 Shneiderman’s 8 Golden Rules
1. Strive for consistency
 lay-out, terminologies, command usage, etc.
2. Enable frequent users to use shortcuts
 recognize the requirements of diverse users and technology. For
instance add features for novices e.g. explanations, support expert
users e.g. shortcuts
3. Offer informative feedback
 for every user action, offer relevant feedback and information,
keep the user appropriately informed, human-computer interaction.
4. Design dialogs to yield closure
 for every user action, offer relevant feedback and information,
keep the user appropriately informed, human-computer interaction.
(e.g. Fill in form  submit  Confirmation)
 Shneiderman’s 8 Golden Rules…
5. Offer error prevention and simple error handling
 prevention and (clear and informative guidance to) recovery;
error management
6. Permit easy reversal of actions
 to relieve anxiety and encourage exploration, because the user
knows s/he can always go back to previous states
7. Support internal locus of control
 make the user feel that s/he is in control of the system, which responds
to his/her instructions/commands.
8. Reduce short-term memory load
 make menus and UI elements/items visible, easily
available/retrievable, ...
 Norman’s 7 Principles [study on your own]

1. Use both knowledge in the world and knowledge in the head.

2. Simplify the structure of tasks.
3. Make things visible: bridge the gulfs of Execution and
Evaluation
4. Get the mappings right - intentions to controls & actions to
event
5. Exploit the power of constraints
6. Design for error
7. When all else fails, standardize.
 HCI design patterns
 An approach to reusing knowledge about successful
design solutions
 A pattern is an invariant solution to a recurrent problem
within a specific context
 HCI design patterns document interaction models that
make it easier for users to understand an interface and
accomplish their tasks
 For patterns to be helpful to the designers and developers
who will make use of them, they need to be findable and
readable
 HCI design patterns …
 Reasons to use design patterns
 Teaching novices some best practices and common
approaches
 Giving teams a common language, reducing
misunderstandings that arise from different vocabulary
 Reducing time and costs in the design and development
lifecycle
 Making usable designs
 Eliminate wasted time spent "reinventing the wheel"
 Ensuring users have a consistent and predictable experience
within an application or service
Questions ??
Thank You