Add a subtype discriminator for each of the supertypes shown in Figure 3-10. Show the di...

From the figure 3-10, the following subtype discriminator can be determined:

• The super type entity “PERSON” includes the attributes of “Name, Address, Gender, Date Of Birth, and Person Type”.

• The super type PERSON is further subdivided into the subtypes of “EMPLOYEE, ALUMNUS and STUDENT”.

• The subtype “EMPLOYEE” acts as the super type for “Faculty and Staff” subtypes.

• The subtype “STUDENT” act as the super type for “GRADUATE STUDENT” and “UNDERGRAD STUDENT” subtypes.

The diagrammatic representation of subtype discriminator in university EER diagram is shown below:

a)

Subtype discriminator for PERSON entity:

• The Entity person is super type.

• Here, the Person Type is a composite attribute of the “PERSON” assigned to the subtype discriminator.

• The notation to specify the subtype discriminator expression is,

Person Type = (either the Employee? = “Y” or

Alumnus? = “Y” or Student? = “Y”)

• Super type, “PERSON” contains three subtypes ”EMPLOYEE”,”ALUMNUS”, and ”STUDENT”.

• Here, the rule “overlap” is applied. Then, the “PERSON” super type may have all the subtype entities “STUDENT”, “ALUMNUS”, and ”EMPLOYEE” at same time.

• From super type “PERSON” to subtype “EMPLOYEE, ALUMNUS or STUDENT” there is a total specialization that is Person has to be either “EMPLOYEE, ALUMNUS or STUDENT”.

b)

Subtype discriminator for EMPLOYEE entity:

• The entity “EMPLOYEE” acts as super type for the Sub type entities “FACULTY” and “STAFF”. at the same time acts as sub type for super type “PERSON”

• Here, the “Employee Type” is an attribute of the “EMPLOYEE” and is a subtype discriminator.

• The notation to specify the subtype discriminator expression is,

Employee Type = (either the “Faculty” or “Staff”)

• Here, the rule “disjoint” is applied. That is the “EMPLOYEE” can be either “FACULTY or STAFF”, but not both at the same time.

c)

Subtype discriminator for STUDENT entity:

• The entity “STUDENT” acts as super type for the Sub type entities “GRADUATE STUDENT and UNDERGRAD STUDENT” at the same time acts as sub type for super type “PERSON”

• Here, the Student Type is an attribute of the “STUDENT” assigned to the subtype discriminator.

• The notation to specify the subtype discriminator expression is,

Student Type = (either the “Grad” or “Undergrad”).

• Here, the rule “disjoint” is applied. This is the “STUDENT” can be either “GRADUATE STUDENT and UNDERGRAD STUDENT”, but not both at the same time.

•

From super type “Student” to subtypes “GRADUATE STUDENT and Undergrad STUDENT”, there is total participation that is “Student” has to be either “Graduate STUDENT” or “UNDERGRAD STUDENT”.

Thus, sub type discriminator is added for each of the super types shown in figure 3-10.