CH 4

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Outline
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 Design rules
 Principles
 Standards
 Guide lines
 Principles to Support Usability
 HCI design patterns
Design Rules
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 The principles of design are the rules a designer must follow to create
an effective and attractive composition.
Interface Design Road Maps
4
Principles to support usability
 Defining Usability: the extent to which a product can be

used by specified users to achieve specified goals with
effectiveness, efficiency and satisfaction in a specified context
of use
 Designing for maximum usability is the goal of interactive
systems design.
 Design rules
 Are rules a designer should follow in order to increase the
usability of the eventual software product
 Provide designers with the ability to determine the usability of
their design decisions.
6 Design Rules…
 Three types of design rules
 Principles - Collections of statements that advice the designer on how to
proceed (e.g., “know the user”). Abstract design rules.
 Standards - Are specific design rules and measurable with limited application
e.g. ISO 9241
 Guidelines - Collections of tests that can be applied to an interface to determine
if it is satisfactory
 Advice on how to achieve principle
e.g., provide an average response time of less than 1sec.

Principles
 Three main categories of principles
 Learnability
 The ease with which new users can begin effective interaction
and achieve maximal performance
 Flexibility
 The multiplicity of ways the user and system exchange
information
 Robustness
 The level of support provided to the user in determining successful
achievement and assessment of goals - goal-directed behaviour
Principles of learnability
A. Predictability
 Determining effect of future actions based on past interaction
history
 Another aspect of predictability allows the user to predict
which operations can or can not be performed on the
interface. This is known as -operation visibility
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?
Cont’d
One way to incorporate predictability is
by designing conventionally. For
example, the magnifying glass icon is
used standardly for search. When users
see this icon in a new interface, they can
predict based on their experience that it
will be used for searching.
Principles of learnability
B. Familiarity
 The familiarity principle allows users to utilize prior knowledge to
understand the interface's features. It deals with how easily users can begin
the interaction based on their initial perception.
 The most common example of familiarity is that of word processors. When
word processors were first introduced, they were made to look similar to
typewriters so users could easily perceive how to begin using them.
 e.g. Guessability, affordance
 Another example is the conventional use of the Recycle Bin to represent

deleted items.
Cont’d
C. Generalizability
 It also refers to extending the knowledge of performing an action on
one interface to a similar action on the same interface.

 An example of generalizability across different interfaces is how the cut/paste
operations are supported with the same shortcuts over numerous applications.
 As another example, generalizability is supported if a user knows how to
draw a rectangle in a drawing application and can apply this knowledge to
sketching a circle in the same application.
 UI standards and guidelines assist/enforce generalizability
Cont’d
D. Consistency : means that the same input/output actions should
perform the same functions with the same behavior. It also concerns the
interface's appearance, where consistency can be incorporated using a pre-
determined color palette
 Consistency should be present across applications and within the same
application as well.
 For example, options on dialog boxes should have the exact placement
throughout the application.
Principles of learnability(ctd)
E. Synthesizability
 refers to the interface allowing users to assess the effect of their actions on
the system state.
 assessing the effect of past actions
 immediate vs. eventual honest
 Immediate honesty: Ideally, the interface should immediately inform
the user of any changes due to their action. This is observed in GUIs.
For example, when a new folder is created on Windows, the user can
immediately see a folder icon named "New Folder."
Cont’d
 Eventual honesty: This is when the user has to perform some actions
to confirm the change. For example, in CLIs, when a new folder is
created, the user has to remember the destination directory and verify
the creation after running some commands.
Principles of flexibility …
 Multiplicity of ways that users and system exchange information
A. Dialogue initiative
 Freedom from system enforced constraints on input dialogue
 In general, we want to maximize the user’s ability to pre-empt the system
and minimize the system’s ability to pre-empt the user.
B. Multithreading
 Ability of system to support user interaction for more than one task at a
time
 Concurrent tasks
Principles of flexibility…
C. 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
D. Customizability
 Modifiability of the user interface by user or system
Principles of robustness
A. Observability
 Ability of user to evaluate the internal state of the system from its
perceivable representation
Principles of robustness
B. Recoverability
 Ability of user to take corrective action once an error has been
recognized
 Reachability, forward/backward recovery, commensurate effort
Principles of robustness …
C. 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.
D. Task conformance
 Degree to which system services support all of the tasks the user
wishes to perform
 task completeness - the coverage issue
Standards and Guidelines for Interactive Systems
 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.
 Set by national or international (ISO) bodies to ensure compliance with a set of
design rules by a large community standards
 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
Cont’d
Guidelines
 More suggestive and general
 Many textbooks and reports full of guidelines
 Applicable during early and later life cycle activities
 Example
 Shneiderman’s 8 Golden Rules
 Norman’s 7 Principles [Reading Assignment]
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. 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
she/he can always go back to previous states
7. Support internal locus of control
 make the user feel that she/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
1. Use both knowledge in the world and knowledge in the head.
 The systems should provide the necessary knowledge within the environment
 And their operation should be transparent to support the user in building an
appropriate mental model of what is going on.
2. Simplify the structure of tasks.
3. Make things visible
4. Get the mappings right - intentions to controls & actions to event
5. Exploit the power of constraints
6. Design for error: Design recovery for the system
7. When all else fails, standardize. If there are no natural mappings then arbitrary
mappings should be standardized
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HCI design patterns
 One way to approach design is to learn from examples that have proven to be
successful in the past:
 So to reuse the knowledge of what made a system - or paradigm - successful.
 Patterns: are an approach to capturing and reusing this knowledge - of

abstracting the essential details of successful design so that these can be applied
again and again in new situations.
 Approach of reusing knowledge about successful design solutions

HCI design patterns …
 Reasons to use design patterns
 Teaching novices some best practices and common approaches
 Reducing time and costs in the design and development lifecycle
 Making more usable designs
 Eliminate wasted time spent "reinventing the wheel"
 Ensuring users have a consistent and predictable experience within an
application or service
Characteristics of patterns
 Capture design practice not theory

 Capture the essential common properties of good examples of
design
 Represent design knowledge at varying levels: social,
organisational, conceptual, detailed
 Are intuitive and readable and can therefore be used for
communication between all stakeholders
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1

 Defining Usability: the extent to which a product can be

e.g., provide an average response time of less than 1sec.

 Another example is the conventional use of the Recycle Bin to represent

one interface to a similar action on the same interface.

 meter(1m, 1 meter, 1),

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

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

 ISO 9241 defines usability as

 Patterns: are an approach to capturing and reusing this knowledge - of

 Approach of reusing knowledge about successful design solutions

 Capture design practice not theory

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