How an Entity in ER Diagram can participate in Unary & Binary Relationship at same time?

Question

A Classical Example of Unary relationship in ER Model is available every where. "Manager manages Employee". The ER Diagram goes as -

Now what if Entity Manager & Employee wants to be associated with some other entities. For Ex- In this classical diagram, how can i add 2 more features:1)Employee operates several Machines 2) Manager attends Meeting. How can i modify this ER Diagram to add these 2 relationships.

I cannot simple relate these two associations with Employee, because a Non-Manager Employee cannot attend meetings.

Answer 1

Relational structure is not good to represent object oriented relationship. So you can draw your objects relation in class diagram, then convert to relational structure with table-per-hierachy, table-per-class etc. And the restraints between objects will be applied in application level or by ORM framework such as Hibernate.