Questions?• Project #2Pros and Cons “To convert temperatures, type the numeric temperature, followed by C if it is in degrees Celsius or F it is in degrees Fahrenheit. The converted temperature will be displayed”GOMS: Application and limitations• Applications– Telephone operator (CPM-GOMS)– CAD system (NGOMSL)– Text editing with the mouse (KLM)• Limitations– Skilled users– Do not deal with error– Do not deal with skill acquisition– Do not deal with high level issues• Functionality• Workload• FatigueCognitive engineering• Gulfs of execution and evaluation [Norman 86]Gulf of evaluation: statistical analysis (1)Real world: Conceptual model:x,y correlated?GulfXY0.67 0.790.32 0.630.39 0.720.27 0.850.71 0.430.63 0.090.03 0.030.20 0.540.51 0.380.11 0.330.46 0.46EvaluationGulf of evaluation: statistical analysis (2)Real world:Gulf00.5100.51XYEvaluationConceptual model:x,y correlated?Gulf of evaluation: statistical analysis (3)Real world:Gulfρ = -.29EvaluationConceptual model:x,y correlated?Gulf of execution: Drawing a rectangle (1)ExecutionGulfMove 90 30Rotate 35Pen down…Real worldConceptual model:Draw a rectangleGulf of execution: Drawing a rectangle (2)Real worldDraw a rectangleRotate the shapeConceptual model:Draw a rectangleExecutionGulfGulf of execution: Drawing a rectangle (3)Conceptual model:Draw a rectangleExecutionGulfReal worldInteraction design: a double gulf?DataConceptualmodelEvaluationExecutionInterfaceRepresentationManipulationInteraction user Interaction designerCognitive engineering example• Move “paper.tex” from ~/conferences/CHI_04to ~/conferences/UIST_04– Using a Unix shell (current directory is ~)– Using a GUI (starting from the desktop, no window open)Direct manipulation • Central ideas– Object understood by their visual characteristic• Using good affordances• Using a good conceptual model and convincing metaphors– Actions understood in term of their effects on the screen• Rapid and incremental• Immediate visual feedback• Easily reversible•Outcome– Direct engagement• the feeling of working directly on the task• No need to know the implementation details– The display becomes reality: the WYSIWYG interfaceGrammatical structure• Object-action (Noun verb)– Modeless– Action always within the context of objects– Examples• Drag and drop…• Select and delete• Action-Object (Verb noun)– Modal• Mode can be dangerous– Often more efficient– Examples• Pick a tool, then use it…Interface metaphors• Definition– Use of one kind of object or idea in place of another to suggest a likeness or analogy between them• Purposed– Leverages our knowledge of familiar, concrete objects/experiences– Transfer this knowledge to abstract computer and task concepts• Examples– Desktop, files, folders, trash can…– Paintbrush in a painting programMetaphors caveats• Too limited– The metaphor restricts interface possibility• Too powerful– The metaphor makes believe that the system can do things it can’t• Too literal or cute– Make it difficult to operate• Mismatched– The metaphor makes it difficult to carry out the taskDirect manipulation: Good or Evil?• Good for intermediate users– Recognition versus recall trade-off• Explicit versus implicit command– “rename each file by adding ‘_old’ to its name”• Limit of reification– How to align an object?• Metaphor might be too restrictive– WYSIAYG: What You See Is All You Get • Applications mix– Direct manipulation• Tools, drag and drop interactions…– Abstraction • Menus, dialog