I m doing a E/R model for a project. I finished the ER model and, for me, all is okay. Maybe not perfect, but it s okay. When I gave the ER model to my teacher, he told me this:
"the m:n relations MUST HAVE some properties"
他说,如果<代码>m:n relationshipn t 则其性质是错误的。 在我看来,<代码>m:n 没有必要对这种关系的属性作出规定,但如果你有适合这种关系的人,那么就应该这样做。
What do you think? Who is wrong in this, me, or my teacher?
注:
读一下,看来他所说的不是由于我的ER diagram,而是一般性发言。 我给他的图表没有关系,因此,在那里,只有实体和教会。
"Must" is too strong. I can see where the JOIN table in an m:n relationship need not have attributes; those are common in my applications.
我也可以看到,它们何时有用。
我对一切形式的狗表示仇恨。 了解规则;知道何时打破规则以及原因。 如果你们的教员如此处理问题,他们就会有更多的教育和知识。
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