design rules

Designing for maximum usability chapter 7 – the goal of interaction design • Principles of usability design rules – general understanding • Standards and guidelines – direction for design

• Design patterns – capture and reuse design knowledge

types of design rules Principles to support usability

• principles Learnability – abstract design rules the ease with which new users can begin effective – low authority interaction and achieve maximal performance – high generality Guidelines Flexibility •standards the multiplicity of ways the user and system exchange – specific design rules information – high authority increasing generality – limited application Standards Robustness • guidelines increasing generality the level of support provided the user in determining successful achievement and assessment of goal- – lower authority increasing authority increasing authority directed behaviour – more general application

Principles of learnability Principles of learnability (ctd)

Predictability Familiarity – how prior knowledge applies to new system – determining effect of future actions based on – guessability; affordance past interaction history – operation visibility Generalizability – extending specific interaction knowledge to new situations Synthesizability – assessing the effect of past actions Consistency – immediate vs. eventual honesty – likeness in input/output behaviour arising from similar situations or task objectives

1 Principles of flexibility Principles of flexibility (ctd)

Dialogue initiative Substitutivity – freedom from system imposed constraints on input dialogue – allowing equivalent values of input and – system vs. user pre-emptiveness output to be substituted for each other – representation multiplicity; equal opportunity Multithreading – ability of system to support user interaction for more than one task at a time Customizability – concurrent vs. interleaving; multimodality – modifiability of the user interface by user Task migratability (adaptability) or system (adaptivity) – passing responsibility for task execution between user and system

Principles of robustness Principles of robustness (ctd)

Observability Responsiveness – ability of user to evaluate the internal state of the – how the user perceives the rate of system from its perceivable representation communication with the system – browsability; defaults; reachability; persistence; operation visibility – Stability

Recoverability Task conformance – ability of user to take corrective action once an error has been recognized – degree to which system services support all – reachability; forward/backward recovery; of the user's tasks commensurate effort – task completeness; task adequacy

Using design rules Standards

Guidelines • set by national or international bodies to ensure compliance by a large community of Design rules designers standards require sound underlying increasing generality Standards • suggest how to increase usability theory and slowly changing technology increasing generality • differ in generality and authority increasing authority • hardware standards more common than increasing authority software high authority and low level of detail

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

2 Guidelines Golden rules and heuristics

• more suggestive and general • “Broad brush” design rules • many textbooks and reports full of guidelines • Useful check list for good design • abstract guidelines (principles) applicable • Better design using these than using nothing! during early life cycle activities • Different collections e.g. • detailed guidelines (style guides) applicable – Nielsen’s 10 Heuristics (see Chapter 9) during later life cycle activities – Shneiderman’s 8 Golden Rules • understanding justification for guidelines aids –Norman’s 7 Principles in resolving conflicts

Shneiderman’s 8 Golden Rules Norman’s 7 Principles

1. Strive for consistency 1. Use both knowledge in the world and 2. Enable frequent users to use shortcuts knowledge in the head. 3. Offer informative feedback 2. Simplify the structure of tasks. 4. Design dialogs to yield closure 3. Make things visible: bridge the gulfs of 5. Offer error prevention and simple error Execution and Evaluation. handling 4. Get the mappings right. 6. Permit easy reversal of actions 5. Exploit the power of constraints, both natural 7. Support internal locus of control and artificial. 8. Reduce short-term memory load 6. Design for error. 7. When all else fails, standardize.

HCI design patterns HCI design patterns (cont.)

• An approach to reusing knowledge about • Characteristics of patterns successful design solutions – capture design practice not theory – capture the essential common properties of good examples • Originated in architecture: Alexander of design • A pattern is an invariant solution to a – represent design knowledge at varying levels: social, organisational, conceptual, detailed recurrent problem within a specific context. – embody values and can express what is humane in •Examples interface design – Light on Two Sides of Every Room (architecture) – are intuitive and readable and can therefore be used for communication between all stakeholders – Go back to a safe place (HCI) – a pattern language should be generative and assist in the • Patterns do not exist in isolation but are linked development of complete designs. to other patterns in languages which enable complete designs to be generated

3 Summary

Principles for usability – repeatable design for usability relies on maximizing benefit of one good design by abstracting out the general properties which can direct purposeful design – The success of designing for usability requires both creative insight (new paradigms) and purposeful principled practice

Using design rules – standards and guidelines to direct design activity

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