2.2 Understand design rules for interactive system

2.2.1 Standards and guidelines of design rules

Types Of Design Rules

• principles – abstract design rules – low authority– high generality

• standards – specific design rules – high authority – limited application

• guidelines – lower authority – more general application

Using Design Rules

• Design rules – suggest how to increase usability – differ in generality and authority

Standards

• set by national or international bodies to ensure compliance by a large community of designers standards require sound underlying theory and slowly changing technology

• hardware standards more common than software high authority and low level of detail

• ISO 9241 defines usability as effectiveness, efficiency and satisfaction with which users accomplish tasks

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 • understanding justification for guidelines aids

in resolving conflicts

2.2.2 Principles to Support Usability

•Learn ability•Flexibility•Robustness

Principles to Support Usability

Learn ability•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 the user

in determining successful achievement and assessment of goal-directed behavior

Principal to support usability

•Learnability•Flexibility•Robustness

Learnability

• The ease with which new users can begin effective interaction and achieve maximal performance

Principles of learnability

• Predictability • Synthesizability • Familiarity • Generalizability • Consistency

Predictability • determining effect of future actions based on

past interaction history • operation visibility

Synthesizability

• Assessing the effect of past actions • immediate vs. eventual honesty

Familiarity

• how prior knowledge applies to new system • guessability; affordance

Generalizability

–extending specific interaction knowledge to new situations

Consistency

• likeness in input/output behaviour arising from similar situations or task objectives

Flexibility

• The multiplicity of ways the user and system exchange information

Principle of Flexibility

•CUSTOMIZABILITY•SUBSTITUITIVITY•DIALOG INITIATIVE•MULTITHREADING•TASK MIGRABILITY

CUSTOMIZABILITY

• modifiability of the user interface by user (adaptability) or system (adaptivity)

SUBSTITUITIVITY

• allowing equivalent values of input and output to be substituted for each other

• representation multiplicity; equal opportunity

DIALOG 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 MIGRABILITY

• passing responsibility for task execution between user and system

Robustness

• the level of support provided the user in determining successful achievement and assessment of goal-directed behavior

Principal of Robustness

•Observability•Recoverability•Responsiveness •Task conformance

Observability

• Extent which user can evaluate the internal state of the system from the representation on the user interface.

Recoverability• Ability to take corrective action upon

recognizing error.• Forward recovery - Ability to fix when we

can’t undo.• Backward recovery - Undo previous error.

Responsiveness• Users perception of rate of communication

with system.• Response time – Time for system to respond

to user actions.

Task conformance

• System support all task user wishes to perform in their expected ways.

• Task completeness : Can system do all tasks ?

• Task adequacy : can user understand how to do tasks? and, does it allow user to define new tasks?

2.2.3 SCHNEIDERMAN’S 8 GOLDEN RULES

INTERFACE DESIGN

Strive for consistency

• Consistent sequences of actions should be required in similar situations

Enable frequent users to use shortcuts

• 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.

Offer informative feedback.

• Offering informative feedback to the users for the actions they do gives the users confidence that they are proceeding in the right direction.

Design dialog to yield closure.

• Sequences of actions should be organized into groups with a beginning, middle and end.

Offer simple error handling.

• A good interface reduces errors , there can be many ways of doing so

Automatic completion

Permit easy reversal of actions

- encourage user to explore new options- Relieve anxiety

Support internal locus of control.

• User satisfaction is high when they feel that they are in control of the system

Every one like control in their hand!

Reduce short-term memory load.

• Human processing is limited in short term memory.Therefore:

- Keep display simple- Reduce windows-motion frequency.