最后一项操作尤为有用，因为它允许我们在树上执行符号操作。
The last operation is particularly useful because it lets us perform symbolic manipulations on the tree.
加快开发和内容创建：大多数BPM工具基于专有符号和执行语言。
Faster development and content creation: Most BPM tools are based on proprietary notations and execution languages.
您可以对这些符号执行各种运算（如计算比率），而对于通过使用功能不那么强大的衡量标准获得的数值，您不能使用这些运算。
You can perform various operations on those symbols (such as computing ratios) that you cannot perform using numerical values obtained using less powerful measurement scales.
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