该系统以PC机为核心单元，实现可视化交互、数据处理和成像；

PC serves as system center, realizing visual interface, data processing and image reconstruction.

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您想要向已存在的模型元素添加一个确认器(核心单元类型)，但是不能访问源代码。

You want to add a validator to an existing model element (the core unit type), but the source code is not accessible.

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查询表达式是在一个树中组装的核心单元或节点，用于指定CriteriaQuery。

Query expressions are the core units or nodes that are assembled in a tree to specify a CriteriaQuery. Figure 1 shows the hierarchy of query expressions defined in the Criteria API.

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