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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该模型定义一组用于存放状态的类，而引擎管理这些信息对象的生命周期。

This model defines a collection of classes for holding the state, and the engine manages the life cycle of these information objects.

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它会将普通的基于字符的状态表示形式从url转换为层次结构对象表示形式(上面介绍的文档模型)。

It transforms the flat, character-based state representation from the URL into a hierarchical object representation (the document model introduced above).

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