Consider the Time Sheet case study application. 1. Give a diagram for the three-layer application architecture discussed in class. Explain the role of each layer and discuss the types of classes needed by each layer. 2. Explain polymorphism through a simple example. Why is it important for OOP? 3. Why is it important to establish a relation between a UI prototype (or even Ul sketches) and use- cases for a given application. Briefly explain. In your opinion what should an analyst start with first (the Ul prototype or the use-case diagrams)? Briefly explain. 4. Discuss the differences between the class diagrams at the different phases of the life-cyle.