模型语义元素通常可能被多个描述全部规范的不同方面的图所引用。
Model semantic elements might be referenced in common by multiple diagrams that depict different aspects of the overall specification.
其次，更细微的原因是模型，不是图，成为系统的结构、语义和行为的记录的表示。
A second, more subtle reason is that the model, not the diagrams, becomes the expression of record for the structure, semantics, and behavior of the system.
uml模型包含语义元素和图，而图是uml模型中语义元素的视图或投影。
A UML model contains semantic elements and diagrams, and the diagrams are views, or projections, of the semantic elements in the UML model.
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