Chapter 6

Performing the riskiest tasks first is another benefit. By bringing risk to the forefront and acknowledging that new conditions can arise at any time, the Spiral Method avoids the hidden time bombs that can occur in the Waterfall Model. When unexpected problems arise, they can be dealt with using the same four-stage approach that works for the rest of the process.

Finally, by repeatedly analyzing after each cycle and building new designs, the practical difficulties with the design-then-implement approach are virtually eliminated. With each cycle, there is more knowledge of the system that can influence the design.

Drawbacks of the Spiral Method

The main drawback of the Spiral Method is that it can be difficult to scope each iteration small enough to gain real benefit. In a worst-case scenario, the Spiral Method can degenerate into the Waterfall Model because the iterations are too long. Unfortunately, the Spiral Model only models the software life cycle. It cannot prescribe a specific way to break down a project into single-cycle iterations because that division varies from project to project.

Other possible drawbacks are the overhead of repeating all four phases for each cycle and the difficulty of coordinating cycles. Logistically, it may be difficult to assemble all the group members for design discussions at the right time. If different teams are working on different parts of the product simultaneously, they are probably operating in parallel cycles, which can get out of synch. For example, the user interface group could be ready to start the discovery phase of the Window Manager cycle, but the core OS group is still in the development phase of the memory subsystem.

The Rational Unified Process

The Rational Unified Process (RUP) is a disciplined and formal approach to managing the software development process. The most important characteristic of the RUP is that, unlike the Spiral Method or the Waterfall Model, RUP is more than just a theoretical process model. RUP is actually a software product, marketed and sold by Rational Software, a division of IBM. Treating the process as software is compelling for a number of reasons:

The process itself can be updated and refined, just as software products periodically have updates.

Rather than simply suggesting a development framework, RUP includes a set of software tools for working with that framework.

As a product, RUP can be rolled out to the entire engineering team so that all members are using the exact same processes and tools.

Like many software products, RUP can be customized to the needs of the users.

RUP as a Product

As a product, the RUP takes the form of a suite of software applications that guides developers through the software development process. The product also offers specific guidance for other Rational products, such as the Rational Rose visual modeling tool and the Rational ClearCase configuration management tool. Extensive groupware communication tools are included as part of the “marketplace of ideas” that allow developers to share knowledge.

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