Since XML data can be very different from relational data, we need a dedicated language to handle XML data efficiently.
由于XML数据可能与关系型数据有很大的差异，因此我们需要一种专门的语言来高效处理XML数据。
The relational data model and use of the SQL language allows for enterprise level performance and scalability.
关系数据库模型和 SQL 语言的使用必须考虑到企业级性能和可伸缩性。
In a relational language, such a query would require a join that might span several data tables and system catalog tables.
而在关系语言中，这种查询需要进行也许跨越了多个数据表和系统目录表的联接。
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