USER INTERFACE DESIGN Not just about the arrangement of media on a screen It’s designing an entire experience for people, hence a “look and feel” User interfaces should be designed to match the skills, experience and expectations of its anticipated users. System users often judge a system by its interface rather than its functionality A poorly designed interface can cause a user to make catastrophic errors Poor user interface design is the reason why so many software systems are never used The Design of Everyday Things - Donald Norman (Doubleday, 1988) “In England I visited a home with a fancy new Italian washer-drier combination, with super-duper multi-symbol controls, to do everything you ever wanted to do with the washing and drying of clothes. The husband (an engineering psychologist) said he refused to go near it. The wife (a physician) said she had simply memorized one setting and tried to ignore the rest.” Norman’s Principles of Usability: 1. Visibility Frequently used functions should be obvious and easy. 2. Mapping Relate interface to mental model 3. Feedback Has an intended action to be done Human Factors in Interface Design 1. Limited short-term memory People can instantaneously remember about 7 items of information. If you present more than this, they are more liable to make mistakes. 2. People makes mistakes When people make mistakes and systems go wrong, inappropriate alarms and messages can increase stress and hence the likelihood of more mistakes. 3. People are different / People have different interaction preferences People have a wide range of physical capabilities. Designers should not just design for their own capabilities. UI Design Principles 1. User familiarity The interface should use terms and concepts which are drawn from the experience of the people who will make most use of the system. 2. Consistency The interface should be consistent in that, wherever possible, comparable operations should be activated in the same way. 3. Minimal surprise Users should never be surprised by the behaviour of a system. 4. Recoverability The interface should include mechanisms to allow users to recover from errors. 5. User guidance The interface should provide meaningful feedback when errors occur and provide context-sensitive user help facilities.