扩展和限制是替换的两个有效方法。但是，根据XML模式规范，联合并不是有效的派生技术(参阅参考资料)。

Extension and restriction are both valid methods for a substitution; however, union is not a valid derivation technique according to the XML Schema specification (see Resources).

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每个连接涉及两个远程操作，联合则将所有三个连接的结果合并。

Each join involves two remote operations, and the union merges the results of all three joins.

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指令查看产品支持战略、战役和战术梯队的联合、合并和组件操作，并为所有信息来源融合提供服务。

Command View supports joint, combined and component operations at the strategic, operational and tactical echelons and serves as the integrator for all information sources.

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