 | Level: Introductory Philippe Kruchten, Staff, Consultant
26 Apr 2004 from The Rational Edge: A sidebar for the article "Going over the waterfall with RUP," available at http://www-128.ibm.com/developerworks/rational/library/4626.html
Aligning the Traditional Waterfall Review Sequence with the Iterative Approach (Sidebar for Going Over the Waterfall with the RUP)
The following text is extracted from the RUP. It matches the RUP iterations with some typical reviews found in traditional waterfall processes, such as DOD-STD-2167A and MIL-STD-498.
The default review sequence for a waterfall lifecycle project is a major review upon completion of each important artifact. For example:
- System Requirements Review (SRR), at the completion of the system specification.
- Software Specification Review (SSR), at the completion of the software requirements specification.
- Preliminary Design Review (PDR), at the completion of the architectural design sections of the software design description.
- Critical Design Review (CDR), at the completion of the detailed design sections of the software design description.
In the RUP, parts of the equivalent artifacts are reviewed as they are completed in each iteration, but the major milestones (and therefore reviews) are aligned with the completion of the phases: Inception, Elaboration, Construction, and Transition. Because of contractual obligations, a project manager wanting to adopt the RUP may have to find a way to reconcile this apparent conflict. Ideally, the project manager should convince the customer that the phase and iteration-based approach in fact gives greater true visibility into project progress, and also reduces risk, so that there is no need for an SRR, an SSR, and so forth. However, this is not always possible, and the project manager has to schedule these reviews at appropriate points. It is possible, in the RUP, to locate the points at which these important artifacts (actually, their RUP equivalents) are essentially complete, although this does not always neatly align with phases or iterations.
Matching traditional waterfall reviews with RUP milestones (see
Figure A-1) is done here by assuming that the relative effort spent
on requirements, design, and the like, will be approximately the
same in the RUP as in the (ideal) waterfall lifecycle, but that
the effort will be distributed differently. The result is
the following:
- The SRR (concerned mainly with the Vision) can be scheduled at the end of the Inception phase.
- The SSR (concerned mainly with the Software Requirements Specification) will occur about a third of the way through the Elaboration phase.
- The PDR (concerned mainly with the Software Architecture
Document) will occur at the end of the Elaboration phase.
- The CDR (concerned mainly with the Design Model) will occur about a third of the way through the Construction phase.
Figure A-1: Matching RUP Milestones with Traditional Waterfall Reviews
For efficiency, the project manager, in consultation with the customer, should attempt to combine these reviews with the prescribed RUP reviews. This is clearly possible for the SRR and the PDR; they can be combined with Lifecycle Objectives Milestone Review and the Lifecycle Architecture Milestone Review, respectively. It is not so obvious for the SSR and CDR. However, observing that almost all projects will have at least two iterations in Elaboration and at least two in Construction, it is recommended that SSR be combined with the Iteration Acceptance Review for the first iteration in the Elaboration phase, and CDR be combined with the Iteration Acceptance Review for the first iteration in the Construction phase. In both cases, there is then good visibility of mature artifacts, with enough time remaining for any required correction — although the iterative approach should cope with this as a matter of course.
About the author | 
| | Philippe Kruchten is former Director and General Manager of the IBM Rational Software
Process Business Unit, in charge of the Rational Unified Process (RUP). He worked with Rational for 13 years, in various functions and places: France, Sweden,
US, and Vancouver, Canada.
Philippe's main interests right now, besides software architecture and design,
are software engineering and the development process. He is campaigning, in
Canada, for the concept of state-licensed professional software engineers. |
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