您还会看到我们用 UML 多重性[0..1]将三个属性置为可选的，如图11所示。

You can also see that we have identified three attributes as optional using UML multiplicity [0..1], as shown in Figure 11.

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但是，关联的多重性经常不是任意的，而依赖于属性值，这不能用图形建模语言，例如UM l类模型来表示。

However, the multiplicity of associations often is not arbitrary, but depends on attribute values, which cannot be expressed with graphical modeling languages such as UML class models.

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可跟踪性，是指一个项目的某种期望属性，说明了诸多重要信息之间的相互关系，是项目保持一定的透明度和能见度。

Traceability, is a desired property of the project where a statement is made about the transparency and visibility of important pieces of information and their interrelationships.

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