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We chose the Mobile design as one of our three final designs.
!asdf!
Suppose Amberlee wants to borrow a book, but she doesn't know what to read. She opens her shelf to see if she has set a book aside to read. She hasn't, so she sees if one of her friends has. She clicks on "friends," and then finds a friend whose taste in books she likes, Jason. She sees what books he is reading, and sees he is reading Moby Dick. She selects the book and sees what the book is about, likes it, adds it to her shelf, and can now start reading a the book.
Efficiency: I sacrificed a bit of efficiency in order to make it more learnable. Despite this, It is very efficient overall, by alternating between three panels, such that no action requires more than three touches.
Learnability: The application makes use of colors and color coding to maximize learnability. It is very simple and has a UI similar to Facebook. Since most high school students are familiar with Facebook, they can easily figure out how to use the application.
Safety: The design is very safe, since it uses large, color-coded icons, such that mistakes are unlikely, and has an easily accessible navigation panel to give access to every section of the application, such that mistakes are easily recoverable. However, it could make more use of clearly distinguishable colors in order to make it more safe. Furthermore, it includes a "Back" button on every page to revert from any page to the previous.