DB基础知识
“数据库”这个陌生而又数据的东东，从进提高班第二年就开始接触，不管是做过的项目还是自考的学习加起来也有3遍了。这只是一个开始，软考又要对数据库进行全面的分析，那么现在就让我们再一次剖析它吧！ 首先，从一副图中进行整体的把控：由于这不是第一次
“数据库”这个陌生而又数据的东东，从进提高班第二年就开始接触，不管是做过的项目还是自考的学习加起来也有3遍了。这只是一个开始，软考又要对数据库进行全面的分析，那么现在就让我们再一次剖析它吧！
首先，从一副图中进行整体的把控：由于这不是第一次接触，所以就针对重难点进一步探讨。即：E-R模型、关系模型。
通过以上的图可以看出数据库技术基础主要包括两大部分即：基础和构成。现在就针对E—R模型和关系模型的转换及关系代数的介绍：
何为E-R模型？
E-R图也称实体-联系图(EntityRelationship Diagram)，提供了表示实体类型、属性和联系的方法，用来描述现实世界的概念模型。
E-R图中的主要构件：
E-R模型的实例：
从上图可看出实体和实体之间存在着各种联系，如：一对一，一对多，多对多。这也正式E-R模型和关系模型转换的关键。喎?http://www.2cto.com/kf/ware/vc/" target="_blank" class="keylink">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"http://www.2cto.com/uploadfile/Collfiles/20140510/2014051008574430.jpg" alt="">
现在明白了关系模型和E-R模型的概念，问题又来了它们之间如何转换呢？
下面就通过简单通俗的语言来介绍：
在E-R模型中如果关系为一对一，一对多，多对多那么在关系模型中转化为：
一对一：将其中一个实体的主键放到另一个实体中。
一对多：将一对的实体中的主键放到多的实体中。
多对多：将两个实体中的主键抽出来另组成一个关系实体。
如果按着这个方法那么在面对这类问题就不用头疼啦！
总结：
以上就是对数据库知识的简单总结，其中对E-R模型和关系模型的转换进行了详细的介绍，在今后的学习中会慢慢的补充优化！
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