7.3 V E R S ION 1 functional and nonfunctional needs. Remember that the material in the first six chapters describes the essence of my motivation here. If you skipped right to the code and haven't read any of the previous material, I encourage you to check it out now. (Of course, you can choose to wait and see what I'm talking about, because we'll experience this phenomenon as we move through this chapter's exercise. I hope that will peak your curios- ity and you'll review the material in the previous chapters.) Here's a simple, high-level description of the system we'll develop. It's the bill payment system cited in previous chapters' discussions: We've been asked to develop a system to handle payment of bills. Prior to paying the bill, the system should apply a discount to the bill in an amount that has been negotiated with the payee (we call this the process of auditing the bill). Applying this discount is a fairly complex process, and a third-party vendor has been commissioned that will apply this dis- count. Additionally, we must integrate with a legacy financials system that must be fed payment information for reconciliation. We'll flesh out additional details as development progresses.