The final issue is that the purchase order itself is defined in the primer as a global element declaration, with a global complex type.

最后一个问题是，购买订单本身在入门中是作为一个全局元素声明的，属于全局复合类型。

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Listing 6 shows a snippet for a new SQL database system capability, including both the element declaration and type definition.

代码清单6为新的SQL数据库系统功能提供了一个代码片段，包括元素声明与类型定义。

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They then traverse a substitution chain of element declarations or a type hierarchy to determine whether the element declaration satisfies the substitution or type derivation requirements.

然后遍历元素声明的代替链或类型层次结构，以决定元素声明是否满足代替或类型衍生要求。

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