迁移仅仅只是生命周期过程中的一部分，因此严格的测试应该包括在项目的各个阶段当中。
Migration is just a part of that lifecycle process, and therefore should involve rigorous testing at each stage of the project.
兼容性应该经过彻底的测试，为以防万一，在迁移周期的早期就应该寻找替代产品。
Compatibility should be tested thoroughly — and early in the migration cycle — in case alternatives need to be sought.
这些战略在迁移所需的工作量和迁移周期方面差异很大，见图 1。
These strategies have widely different characteristics with respect to migration effort and migration period, as shown in figure 1.
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