ER Diagram Entity without attribute

Question

I have designed an er-diagram and have an entity without any attributes. I need this entity (Item) to create a many-to-many relationshop but I guess there is a way to make this more efficient and getting rid of the entity without attributes.

ER DIAGRAM:

Thanks

Answer 1

As I can see from your diagram your Item isn't just entity without attributes. It's a base type for your BAGEL and DRINK (you can think of this relationship as inheritance in OOP languages).

There are some techniques to work with inheritance in database world. So this Item is not a problem for ER-diagram.

Answer 2

ITEM should have at least one attribute - an identifier. A supertype's primary key can be reused as a foreign primary key in its subtypes.