E-R diagram and relationships Suppose we have two entities $A$ and $B$ and some relationship between them. If there is an $M:N$ relationship between them (i.e. an $M$ on the line connecting $A$ to the relationship and an $N$ connecting the relationship to $B$), how do we read this? Would it be the following: A single instance of $A$ is related to $N$ of $B$ and a single instance of $B$ is related to $M$ of $A$?
You got it right, I think.


$1 : N$ means: Any $A$ may be connected with any number of $B$, but every $B$ is connected to (exactly) one $A$.

Example: (Biological) Mothers and children.
$M : 1$ means the same, just reversed.
$M : N$ means that any $A$ may be connected with any number of $B$ and vice versa.

Example: Teachers and students.