design rules.ppt
- 2. Design Rules Designing for maximum usability – the goal of interaction design Principles of usability general understanding Standards and guidelines – direction for design Design patterns – capture and reuse design knowledge
- 3. 1. We require design rules, which are rules a designer can follow in order to increase the usability of the eventual software product. 2. We can classify these rules along two dimensions, based on the rule’s authority and generality. 3. By authority, we mean an indication of whether or not the rule must be followed in design or whether it is only suggested. 4. By generality, we mean whether the rule can be applied to many design situations or whether it is focused on a more limited application situation.
- 4. types of design rules • Principles(derived from knowledge of the psychological, computational and sociological aspects of the problem domains) – abstract design rules – low authority – high generality • Standards(more important that the theory underlying them be correct or sound) – specific design rules – high authority – limited application • Guidelines(more technology oriented) – lower authority – more general in application
- 5. Principles to support usability 1.Learnability the ease with which new users can begin effective interaction and achieve maximal performance. 2. Flexibility the multiplicity of ways in which the user and system exchange information. 3.Robustness the level of support provided the user in determining successful achievement and assessment of goal- directed behaviour.
- 6. 1.Principles of learnability Predictability – determining effect of future actions based on past interaction history. – Operation visibility refers to how the user is shown the availability of operations that can be performed next. Synthesizability – ability of the user to assess the effect of past operations on the current state. – immediate vs. eventual honesty
- 7. Principles of learnability (ctd) Familiarity – The familiarity of an interactive system measures the correlation between the user’s existing knowledge and the knowledge required for effective interaction – guessability; affordance (intrinsic properties of any visual object that suggest to us how they can be manipulated) Generalizability – Users often try to extend their knowledge of specific interaction behavior to situations that are similar but previously unencountered. This is called generalization. Consistency – likeness in input/output behaviour arising from similar situations or task objectives. – Familiarity can be considered as consistency with respect to past real-world experience, and generalizability as consistency with respect to experience with the same system or set of applications on the same platform.
- 8. Summary of principles affecting learnability
- 9. 2.Principles of flexibility Dialogue initiative – freedom from system imposed constraints on input dialogue – system vs. user preemptiveness Multithreading – ability of system to support user interaction for more than one task at a time – concurrent vs. interleaving; multimodality Task migratability – Task migratability concerns the transfer of control for execution of tasks between system and user.
- 10. Principles of flexibility (ctd) Substitutivity – allowing equivalent values of input and output to be substituted for each other – representation multiplicity; equal opportunity Customizability – modifiability of the user interface by user (adaptability) or system (adaptivity)
- 11. flexibility
- 12. 3. Principles of robustness Observability – ability of user to evaluate the internal state of the system from its perceivable representation – browsability; defaults; reachability; persistence; operation visibility Recoverability – ability of user to take corrective action once an error has been recognized – reachability; forward/backward recovery; commensurate effort
- 13. Principles of robustness (ctd) Responsiveness – how the user perceives the rate of communication with the system – Stability Task conformance – degree to which system services support all of the user's tasks – task completeness; task adequacy
- 14. Summary of principles affecting robustness
- 15. Using design rules Design rules • suggest how to increase usability • differ in generality and authority increasing authority increasing generality Standards Guidelines increasing authority increasing generality
- 16. 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
- 17. 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
- 18. Golden rules and heuristics • “Broad brush” design rules • Useful check list for good design • Better design using these than using nothing! • Different collections e.g. – Nielsen’s 10 Heuristics – Shneiderman’s 8 Golden Rules – Norman’s 7 Principles
- 19. Shneiderman’s 8 Golden Rules 1. Strive for consistency 2. Enable frequent users to use shortcuts 3. Offer informative feedback 4. Design dialogs to yield closure 5. Offer error prevention and simple error handling 6. Permit easy reversal of actions 7. Support internal locus of control 8. Reduce short-term memory load
- 20. Norman’s 7 Principles 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. 5. Exploit the power of constraints, both natural and artificial. 6. Design for error. 7. When all else fails, standardize.
- 21. HCI design patterns • An approach to reusing knowledge about successful design solutions • Originated in architecture: Alexander • A pattern is an invariant solution to a recurrent problem within a specific context. • Examples – Light on Two Sides of Every Room (architecture) – Go back to a safe place (HCI) • Patterns do not exist in isolation but are linked to other patterns in languages which enable complete designs to be generated
- 22. HCI design patterns (cont.) • 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 – embody values and can express what is humane in interface design – are intuitive and readable and can therefore be used for communication between all stakeholders – a pattern language should be generative and assist in the development of complete designs.
- 23. 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