ER-Diagram: Can an ENTITY be an ATTRIBUTE to ANOTHER ENTITY?

Question

I have an entity called Employee. One of the attributes of employee can be his/her designation .

I have made the Designation also as an entity . Its attributes could be desg_ID and Design_name.

So my question is, can Designation be an entity and an attribute for the same ER model. Or is it conceptually wrong.

If you think Designation is should not be considered as an entity but only an attribute, please suggest so as well.

Thank You :)

Answer 1

May an attribute be an entity as well?

This sounds really confusing, but I'd say that's not possible. However, you could have an attribute referencing a specific entity.

Should a "Designation" be its own entity?

IMO this really depends on how it's handled or what you consider a "Designation". If there's a strict 1:1 relation between an Employee and a Designation, then it's quite obsolete and it could be part of the actual Employee. If it's possible to have more than one Designation and/or a Designation might be reassigned/moved/swapped, then yes, it should be its own entity IMO.

Answer 2

It sounds a bit like you are normalizing your model. If you think Designation can be its own table then, conceptually, it should be considered a building block in your model.

I think the other part of you question relates to foreign keys (FK). Yes, your Employee entity can have a Designation ID FK, for example.