一个1:N联系可转换为一个独立的关系模式，关系的码为
A) N端实体的码
B) 实体的码
C) 各实体码的组合
D) 每个实体的码
参考答案：A
解析： 从E-R图向关系模式转换时，需遵循一定的原则，对于实体间不同类型的联系，可分为几种情况。对于1: N的联系，可以转换为一个独立的关系模式，也可与N端的对应模式合并。如果转换为一个独立的关系模式，则与该联系相连的各实体的码及联系本身的属性均转换为关系的属性，而关系的码为N端实体的码。
Once there lived two brothers. The elder was called Simon and the younger was Victor. They always each other. Every day they worked from morning night, getting as much grain谷物 as possible from their fields. One late autumn evening, after their work was done, Simon said to his wife, "Victor got married last month. He has many bills to . I think I will put a bag of rice in his barn谷仓." "Oh, that's a good idea," said his wife. "But please don't tell him," said Simon, "If he knows I put the rice there, he will take it.” So, late that night Simon took a bag of rice to Victor's barn. The next day, while looking at his own barn, he was surprised. "I took a bag of rice to Victor's house last night, I still have the same number of bags in my barn. did that happen?" Simon decided to take bag of rice to his brother's barn that night. But the next morning, he found the same number of bags in his barn again! "This is very strange," he thought. That night he tried again. He carried a large bag of rice on his shoulder, and went out to his younger brother's house. In the bright moonlight, he could see someone down the road. He was carrying something on his shoulder as well. "Younger Brother!" Simon cried when he came near the man , "What are you doing?" "I was you, Older Brother," said Victor, "Your family is larger than mine. I thought you needed more rice. “The two brothers quickly that they took rice to each other. They laughed about what had happened. "It is good to have a brother like you," they both said. And they lived happily ever since.
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