问题 填空题

关系的数据操纵语言按照表达式查询方式可分为两大类:关系代数和【 】。

答案

参考答案:关系演算

解析:关系代数是一种抽象的查询语言,是关系数据操纵语言的一种传统表达方式,它是用对关系的运算来表达查询的。关系演算是以数理逻辑中的谓词演算为基础的。按谓词变元的不同,关系演算可分为元组关系演算和域关系演算。

阅读理解

阅读下面短文,根据短文内容,补全表格中所缺的信息。每空最多填写三个单词。

     The idea of Mother's Day is a very old idea. It was started by the ancient Egyptians (埃及人), who

celebrated (庆祝) a day to honour (向……表示敬意) Isis, the mother of the pharaohs. The early Christians

(基督教徒) celebrated a day to honour Mary, the mother of Jesus.

     Later, English Christians celebrated to honour all mothers. This English holiday was called "Mothering

Sunday".When the English came to America, they did not have time for Mothering Sunday, so the holiday

was not celebrated in America. In 1914, the U.S passed a law which designated (规定) the second Sunday

in May as Mother's Day to honour the mothers who had lost sons in war.

     Today, Mother's Day is celebrated in many other countries for all mothers. In Canada, Australia, New

Zealand, Mother's Day is celebrated on the same day as in the United States-the second Sunday in May.

Children give their mothers cards, gifts, and flowers. Schools plan Mother's Day's special activities.

     In China, the holiday is celebrated to show the respect (尊重) the Chinese have for the old people, and

the love they have for their parents. Ten top mothers are chosen by the government. People all over the

country try different ways to help mothers who are poor.

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