The derived relational algebra operators are widely used in the relational database query languages.

关系代数的派生算子在关系数据库查询语言中得到了广泛应用。

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Traditional relational database query language SQL is designed for relational tables, and not suitable for XML or GML semistructured data;

传统的关系数据库查询语言SQL是针对平面的二维关系数据而设计的，并不适合XML/GML半结构化数据的查询；

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Based on this model, this paper constructs two different kinds of medium relational database query languages: medium relational calculus and medium relational algebra.

给出了中介关系数据模型，在此基础上构造了两类不同的中介关系数据库查询语言：中介关系演算和中介关系代数。

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This traditional database platforms, known as relational database management systems (RDBMS) all use a language called SQL (structured query language).

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With a relational database, you start with the domain objects, and represent them in a way that guarantees that virtually any query can be expressed.

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