模型的主实例保持长期状态，并提供应用程序逻辑；而视图使用的副本实际上是一个可任意使用的数据访问对象。

The primary instance of the model is keeping long-term state and providing application logic; the copy used by the view is essentially a disposable data-access object.

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通常，访问器工厂使用路径表达式来定位特定的文档节点，或在状态文档模型中创建阶段（甚至阶段的完整路径）。

Typically, the accessor factory uses a path expression to locate a particular document node or to create a node (or even a complete path of nodes) in the state document model.

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可以使用工具、报告和查询来评价模型的状态，并追踪访问入侵情况。

Metrics, reports, and queries can be used to assess the state of the models, as well as to track access violations.

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