During the early days of a product development life cycle, it is difficult to pin down the cost, schedule, or product quality. But some projects, for very important reasons, need to complete by a specific date. When fixed-phase scheduling is employed, the project phases are apportioned from the top down and scheduled according to the required completion date. (See "Phased Estimating" and "Apportioning" in Chapter 8.) At the end of each phase, the scope of the project is reevaluated (functionality is added or removed) to fit the remaining schedule (see Figure 9.6).
Positive. Since functionality can be added as well as removed, the project will meet the schedule with the best possible product because it was consciously rescoped several times. Quality (product performance) will remain high with this method, because quality-oriented tasks won't be sacrificed at the last minute to meet the schedule.
Negative. Not every product lends itself to functionality changes several times during the life cycle. The design for many products is holistic, encompassing all the functions. During construction of a house, for instance, it isn't appropriate to add another bedroom and bathroom just because the project is ahead of schedule or under budget.
Product development life cycle
Requirements Design Construction
Design Design Design Build Build Build Test Test Test
Fixed completion date
• Use apportioning to determine the duration of each phase given the amount of total development time available.
• Break down the construction phase into detailed design-build-test phases. These subphases are used to control scope, because a shippable product is created at the end of every construction subphase.
• At the end of every product development phase, including requirements, design, and all construction subphases, reestimate how much functionality can be built without changing the ship date.
• Be sure the functionality is prioritized, ensuring only low-priority functions are cut during each phase review.
• If everything is ahead of schedule, add another design-build-test phase to add more functionality.
Best application. Projects whose delivery date is set and whose products can be scaled up or down during development without compromising design lend themselves best to this method. Software (including information systems) is probably the best candidate for fixed-phase estimating, because most software designs are modular. In addition, it's critical that these products meet their delivery date because their market success often depends on beating a competitor to the punch.
Because fixed-phased scheduling does require product scope changes, the project manager must be prepared to present hard choices to the customer and other stakeholders several times during the project.
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