$1-$a$-)$ What are the referential integrity constraints in this model? Write them in the form of FK$--->$PK$.$

Assume that the value of MGR in the last row is NULL.

Hint: A PK may consist of more than one attribute.

b$-)$ Transform this relational database model to its equivalent E$/$R model.

Hint: Notice which tables transform to entities and which tables to relationships. Do not forget to

specify the cardinality constraints in$($max$,$min$)$ notations.