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1 User Interface Design CIS 375 Bruce R. Maxim UM-Dearborn.

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1 1 User Interface Design CIS 375 Bruce R. Maxim UM-Dearborn

2 2 Principles of Good Design State and action alternatives are visible Conceptual model is consistent with system image Interface should include mappings that reveal relationships among task stages User should receive continuous feedback

3 3 8 Golden Rules of User Interface Design Strive for consistency Enable short-cuts for frequent users Informative feedback Design dialogs to yield closure Offer simple error handling Permit easy reversal of actions Support internal locus of control Reduce short-term memory load on user

4 4 Place User in Control Define interaction in such a way that the user is not forced into performing unnecessary or undesired actions Provide for flexible interaction (users have varying preferences) Allow user interaction to be interruptible and reversible Streamline interaction as skill level increases and allow customization of interaction Hide technical internals from the casual user Design for direct interaction with objects that appear on the screen

5 5 Reduce Memory Load Reduce demands on user's short-term memory Establish meaningful defaults Define intuitive short-cuts Visual layout of user interface should be based on a familiar real world metaphor Disclose information in a progressive fashion

6 6 Make Interface Consistent Allow user to put the current task into a meaningful context Maintain consistency across a family of applications If past interaction models have created user expectations, do not make changes unless there is a good reason to do so

7 7 User Interface Design Models Design model –incorporates data, architectural, interface, and procedural representations of the software User model (end user profiles) –novice, –knowledgeable intermittent user –knowledgeable frequent users User's model or system perception –user's mental image of system System image –look and feel of the interface and supporting media

8 8 User Interface Design Process (spiral model) User, task, and environment analysis and modeling Interface design Interface construction Interface validation

9 9 Task Analysis and Modeling - 1 Software engineer –studies tasks human users must complete to accomplish their goals without the computer –maps these into a similar set of tasks that are to be implemented in the user interface Software engineer –studies existing specification for computer solution –derives a set of tasks that will accommodate the user model, design model, and system perception

10 10 Task Analysis and Modeling - 2 Software engineer –may devise an object-oriented approach by observing the real world objects and user actions (use cases) –models the interface objects after their real world counterparts

11 11 Interface Design Activities Establish goals and intentions for each task Map each goal/intention to a sequence of actions (methods for manipulating objects) Specify the action sequence of tasks and subtasks (user scenario) Indicate the state of the system at the time the user scenario is performed Define control mechanisms Show how control mechanisms affect the state of the system Indicate how the user interprets state of the system from information provided through the interface

12 12 Interface Design Issues System response time –time between the point at which user initiates some action and the time the system responds User help facilities –integrated, context sensitive help –add-on help Error information handling –messages should be non-judgmental –describe problem precisely –suggest valid solutions

13 13 Data Display Guidelines Consistency Efficient information assimilation by user Minimal memory load on user Compatibility between data display and data entry Flexibility of user control over data display

14 14 Data Entry Guidelines Consistency Minimal user input actions Minimal memory load on user Compatibility between data entry and data display Flexible user control

15 15 Getting User’s Attention Intensity (2 levels only) Marking (e.g. underscore) Fonts (up to 3) Inverse video Blinking (2 to 4 hertz) Color (up to 4 standard colors) Color blinking Audio

16 16 Factors affecting choice of evaluation methodology Stage of design Novelty of product Expected number of users Criticality of interface Cost of product and budget for testing Experience of design and evaluation teams

17 17 User Interface Evaluation 1.Preliminary design 2.Build first interface prototype 3.User evaluates interface 4.Evaluation results studied by designer 5.Design modifications made 6.Build next prototype 7.If interface is not complete then go to step 3

18 18 User Interface Evaluation Criteria - 1 Length and complexity of written interface specification –indicate of amount of learning required by system users Number of user tasks and the average number of actions per task –indicate of interaction time and overall system efficiency

19 19 User Interface Evaluation Criteria - 2 Number of tasks, actions, and system states in the design model –indicate of the memory load required of system users Interface style, help facilities, and error handling protocols –indicate of system complexity and likely degree of acceptance by the users

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