The remaining chapters of Part I present several case studies aimed at demonstrating important techniques used in performance analysis and capacity planning. Each case study has specific learning objectives. For example, in this chapter, a database service example is used to describe how service demands are obtained from different types of measurements and how a model is constructed and used to answer several "what-if" questions. (What if an extra disk is purchased? How much it improves user response time? Would adding a second processor be more cost effective?) The data, computations, and graphs presented in this chapter are easily generated from the provided MS Excel workbooks: DBServiceExample.xls, OpenQN-Chap5.xls, and k-means.xls.