design rules general understanding Standards and guidelines - PDF document

design rules Designing for m axim um 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 interaction and achieve m axim al perform ance – low authority – high generality Guidelines increasing generality increasing generality Flexibility • standards the m ultiplicity of ways the user and system exchange – specific design rules inform ation – high authority Standards Robustness – lim ited application • guidelines the level of support provided the user in determ ining successful achievem ent and assessm ent of goal- – lower authority increasing authority directed behaviour increasing authority – m ore general application Principles of learnability Principles of learnability (ctd) Fam iliarity Predictability – how prior knowledge applies to new system – determ ining 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 sim ilar situations or task objectives 1

Principles of flexibility Principles of flexibility (ctd) Dialogue initiative Substitutivity – freedom from system im posed constraints on input – allowing equivalent values of input and dialogue output to be substituted for each other – system vs. user pre-em ptiveness – representation m ultiplicity; equal opportunity Multithreading – ability of system to support user interaction for m ore than one task at a tim e Customizability – concurrent vs. interleaving; m ultim odality – m odifiability of the user interface by user Task m igratability (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 com m unication with the system – browsability; defaults; reachability; persistence; – Stability operation visibility Recoverability Task conformance – ability of user to take corrective action once an error – degree to which system services support all has been recognized of the user's tasks – reachability; forward/ backward recovery; – task com pleteness; task adequacy com m ensurate effort Using design rules Standards increasing generality Guidelines increasing generality • set by national or international bodies to ensure compliance by a large community of designers standards require sound underlying Design rules Standards theory and slowly changing technology • suggest how to increase usability • differ in generality and authority • hardware standards more common than increasing authority increasing authority software high authority and low level of detail • ISO 9241 defines usability as effectiveness, efficiency and satisfaction with which users accom plish tasks 2

Guidelines Golden rules and heuristics • m ore suggestive and general • “Broad brush” design rules • m any 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 – Shneiderm an’s 8 Golden Rules • understanding justification for guidelines aids – Norm an’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 knowledge in the head. 2. Enable frequent users to use shortcuts 2. Sim plify the structure of tasks. 3. Offer inform ative feedback 3. Make things visible: bridge the gulfs of 4. Design dialogs to yield closure Execution and Evaluation. 5. Offer error prevention and simple error 4. Get the m appings right. handling 5. Exploit the power of constraints, both natural 6. Permit easy reversal of actions and artificial. 7. Support internal locus of control 6. Design for error. 8. Reduce short-term m em ory load 7. When all else fails, standardize. HCI design patterns HCI design patterns (cont.) • Characteristics of patterns • An approach to reusing knowledge about – capture design practice not theory successful design solutions – capture the essential common properties of good examples • Originated in architecture: Alexander of design – represent design knowledge at varying levels: social, • A pattern is an invariant solution to a organisational, conceptual, detailed recurrent problem within a specific context. – embody values and can express what is humane in • Exam ples interface design – are intuitive and readable and can therefore be used for – Light on Two Sides of Every Room (architecture) 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 m axim izing 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 paradigm s) and purposeful principled practice Using design rules – standards and guidelines to direct design activity 4