The amount of unproven work is very small, which allows the team
to correct some mistakes on the fly, as when coding reveals a design flaw, or when a customer review
reveals that a user interface layout is confusing or ugly.
The tight feedback loop also allows XP teams to refine their plans quickly. It??™s much easier for a customer
to refine a feature idea if she can request it and start to explore a working prototype within a few days.
The same principle applies for tests, design, and team policy. Any information you learn in one phase
can change the way you think about the rest of the software. If you find a design defect during coding
or testing, you can use that knowledge as you continue to analyze requirements and design the system
in subsequent iterations.
Iteration
$
1 week
$ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $
Iteration
Iteration
Iteration
Plan
Deploy
Analysis
Design
Code
Test
$ = Potential release
Figure 3-2. XP lifecycle
* Productivity is notoriously difficult to study. I??™m not aware of any formal research on XP productivity, although anecdotal evidence
indicates that agile teams are more productive than traditional teams.
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