Expand an infinite ERD

i have an erd for a school assignment that contains a many to many relationship that as far as i can tell is un-expandable. I have a class that can be taught by many teachers (as in many teachers in the same room at the same time teaching the same people) and one teacher is assigned as the head teacher, so as far as i can see, one class can be taught by many teachers and many teachers can teach the same class (at the same time). Has anyone got any idea how i could expand this?

I have tried making a week entity eg group. so one class is taugt by one group and one group can teach many classes but i still end up with the issue of one group can have many teachers and many teachers can be in a group. Every way i look开发者_运维问答 at i end up with a many to many relationship between teacher and either class or the weak entity, any help would be greatly appreciated. thanks

The usual (and best) approach to modeling m:n relationships is to create an intermediate association.

In this case you would have a 1:m relationship between Class and the association (since each class can be associated with many teachers) and also a 1:m relationship between Teacher and the associtaion (since each teacher can be associated many classes).

When it comes to creating tables, the association becomes a table in its own right, with foreign keys to both Class and Teacher, thus linking them together.