This is the first time that this example is using a relation as a declarative statement to define an expression (in other words, a value assignment) instead of using it for model-to-model mapping.

这是本例子第一次把关联作为一个定义表达式(换句话说，一个赋值语句)的声明性陈述来使用，而不是用它作模型到模型的映射。

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For example, some problems lend themselves to more succinct expression as a state machine than as a set of declarative rules.

比如，有些问题使用状态机比使用声明性规则具有更加简洁的表述。

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