关联实体与关联关系属性的区别？ [英] Difference between associative entity and associative relationship attribute?

问题描述

关联实体和关联关系属性有什么区别？在我的书现代数据库管理（Hoffer，第11版）中，作者指出，两者之间有区别。尽管如此，它并没有真正解释为什么会有所区别，相反，它只是举例说明它们是如何不同的。

从我收集的内容中，具有与其相关联的单个属性的关系是关联关系属性，并用虚线该矩形内具有该属性的圆角矩形。而关联实体是多个描述关系的属性。两者只能用于ER图中的多对多关系。我的思维过程是否正确？

编辑 - 另外，我忘了提及关联实体，他们还有一个属性是唯一的标识符，至少这就是我的想法。

解决方案

在ER图中，M：N关系可以具有描述关系的关联实体或单个关联属性。不同之处在于，关联实体必须具有唯一的标识符和关联属性。根据该书，关联实体必须具有：

  1  - 参与实体类型的所有关系都是M：N关系
 
 2  - 结果关联实体类型对最终用户具有独立意义，并具有标识符
 
 3-该实体具有一个或多个属性
 
 4  - 实体参与独立于相关关系相关实体的1个或多个关系。 
  

What is the difference between an associative entity and an associative relationship attribute? In my book titled, Modern Database Management (Hoffer, 11th edition), the author states that there is a difference between the two. Though, it doesn't really explain why there's a difference, instead, it just gives examples of how they're different.

From what I gather, a relationship that has a single attribute associated with it is an associative relationship attribute and is denoted with a dashed line to a rounded-corner rectangle with that attribute inside that rectangle. Whereas an associative entity is more than one attribute that describe the relationship. Both can only be used for many-to-many relationships in ER diagramming. Is my thought process correct?

Edit - Also, I forgot to mention, with associative entities, they also have an attribute that is an unique identifier, at least, this is what I think.

解决方案

In ER diagramming, M:N relationships can have associative entities OR single associative attributes that describe the relationship. The difference is, associative entities must have a unique identifier and associative attributes don't. According to the book, an associative entity must have:

1-all the relationships for the participating entity types are M:N relationships 

2-the resulting associative entity type has independent meaning to the end user and has an identifier 

3- the entity has one or more attributes 

4-the entity participates in 1 or more relationships independent of the entities related in the associated relationship.

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