Question

A company database needs to store information about employees (identified by ssn, with salary and phone as attributes), departments (identified by dno, with dname and budget as attributes), and children of employees (with name and age as attributes) 

Employees work in departments; each department is managed by an employee; a child must be identified uniquely by name when the parent (who is an employee; assume that only one parent works for the company) is known. We are not interested in information about a child once the parent leaves the company. 

Q.4.1 Draw an ER diagram that captures this information and/ or showcase your answer using table names and relationships.

 Q.4.2 Explain the difference between a weak and a strong entity set.

Answer 1

4.1 Below is the ER diagram shown where the Children entity is a weak entity type since its record depends on its Parent to be the company's employee. Hence, the relation of the Parent is also a weak relationship; this is shown by double diamond.

4.2 A weak entity set has its existence dependent upon some other string entity set just like in previous example record of children are maintained only if their Parent is an employee while the existence of a strong entity type is not dependent upon any other entity.

Please comment for any clarification.