196 Chapter 9. Identifying the Tasks and Activities As described in Chapter 8, "Creating the Work Breakdown Structure," building a product-oriented work breakdown structure (WBS) involves decomposing a large activity (the whole project) into successively smaller activities (top-down approach) until the work is described in detail to manage properly. Alternatively, it involves brainstorming everything that needs to be done as detailed ac- tivities and arranging them until enough are present to carry out and manage the work (bottom-up approach). In either case, identifying the right activities for the work is paramount. The triple constraint for any project (scope, schedule, cost) is largely dependent on getting the scope right because it usually drives the schedule and cost of a software development project. In Chapter 10, "Software Size and Reuse Estimating," we'll see how the product-oriented WBS is the primary determinant of the scope and cost portions for software projects, as product size is the primary determinant of effort for software, an intellectual product. In this chapter, we explore the identification of tasks and activities that software engineers use to produce the elements of a product-oriented WBS, and we consider how to arrange them for best effect in the life cycle models described in Chapter 4, "Selecting Software Development Life Cycles."