Drawing Organizational EER Diagrams
A nonprofit organization depends on a number of different types of persons for its successful operations. The organization is interested in the following attributes for all of these persons: SSN, Name, Address, City/State/Zip, and Telephone. Three types of persons are of greatest interest: employees, volunteers, and donors. Employees have only a Date Hired attribute, and volunteers have only a Skill attribute. Donors have only a relationship (name Donates) with an Item entity type. A donor must have donated one or more items, and an item may have no donors, or one or more donors. There are persons other than employees, volunteers, and donors who are of interest to the organization so that a person need not belong to any of these three groups. On the other hand, at a given time, a person may belong to two or more of these groups (e.g., employee and donor). Draw an EER diagram for the above problem. Add a subtype discriminator (name Person Type) to the diagram you created.
In the diagram, the “Person” entity type is the supertype for the three subtypes: Employee, Volunteer, and Donor. Each subtype has its own set of attributes, in addition to the common attributes inherited from the supertype.The subtype discriminator “Person Type” is used to indicate which subtype a particular person belongs to. For example, if a person has a value of “Employee” in the “Person Type” attribute, then that person is an Employee and will have a “Date Hired” attribute. Similarly, if a person has a value of “Donor” in the “Person Type” attribute, then that person is a Donor and will have a relationship with the Item entity type.
Further, the “Item” entity type is not shown in this diagram, as its attributes are not relevant to the problem at hand. The relationship between Donors and Items is represented using a diamond-shaped relationship with the “name Donates” label.
