In many cases, these standards are defined for a particular industry and express the structure of relevant data in the form of XML schema.

在许多情况下，这些标准是为某一特定行业而制定的，并且以XML模式的形式表达相关数据的结构。

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The XML Schema specification (See the Resources section) provides a rich data model that enables you to express sophisticated structure and constraints on your data.

XML模式规范(请参见参考资料部分)提供了一个丰富的数据模型，允许对数据上的复杂结构和约束进行表述。

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Rails migrations let us express the differences between two versions of our schema, and the data they contain, in code (see the article " Rails migrations").

Rails 迁移使我们能够用代码表示模式的两个版本之间的差别，和它们所包含的数据之间的差别（请参阅文章 “ Rails 迁移”）。

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