3.4 Participation Constraints

Participation indicates whether all or only some entity instances participate in a relationship:

1.    TOTAL PARTICIPATION (Mandatory) — Every instance of the entity type MUST participate in the relationship. Drawn as a DOUBLE LINE. E.g., every STUDENT must BELONG-TO a DEPARTMENT.

2.    PARTIAL PARTICIPATION (Optional) — Some instances may not participate. Drawn as a SINGLE LINE. E.g., not every STAFF member has a DEPENDENT.

Complete ER Diagram Example: Newgate University Database

ENTITIES: STUDENT, COURSE, LECTURER, DEPARTMENT, EXAMINATION

 

STUDENT attributes: MatricNo (key), FirstName, LastName, DateOfBirth, Email, PhoneNo (multi-valued), Level

COURSE attributes: CourseCode (key), CourseName, CreditUnits, Semester

LECTURER attributes: StaffID (key), FullName, Rank, Specialisation

DEPARTMENT attributes: DeptCode (key), DeptName, Faculty

EXAMINATION attributes: ExamID (key), ExamDate, Venue, Duration

 

RELATIONSHIPS:

1.    STUDENT ENROLS-IN COURSE [M:N, Total:Total] — Many students enrol in many courses

2.    LECTURER TEACHES COURSE [1:N, Partial:Total] — One lecturer teaches many courses; each course is taught by one lecturer

3.    STUDENT BELONGS-TO DEPARTMENT [N:1, Total:Partial] — Many students belong to one department

4.    COURSE BELONGS-TO DEPARTMENT [N:1, Total:Partial] — Many courses belong to one department

5.    STUDENT SITS EXAMINATION [M:N] — Students sit many examinations; each examination has many students

ER Diagram Notation Summary

Symbol/Representation

Entity Type (strong)

Rectangle

Entity Type (weak)

Double Rectangle

Attribute (simple)

Oval

Attribute (multi-valued)

Double Oval

Attribute (derived)

Dashed Oval

Key Attribute

Underlined text in Oval

Relationship

Diamond

Identifying Relationship (weak)

Double Diamond

Total Participation

Double Line

Partial Participation

Single Line

 

 Reading List / References

Elmasri, R. & Navathe, S. B. (2016). Fundamentals of Database Systems, Chapter 3: ER Model. Pearson.

Connolly, T. & Begg, C. (2015). Database Systems, Chapter 12: ER Modelling. Pearson.

Chen, P. P. (1976). The Entity-Relationship Model: Toward a Unified View of Data. ACM Transactions on Database Systems, 1(1), 9-36.

Activities

Self-Assessment Quiz: 1. What is the difference between an entity and an entity type? 2. Name FOUR types of attributes and give an example of each from a STAFF entity. 3. What is a weak entity? Give a Nigerian example. 4. A department has many lecturers but each lecturer belongs to only one department. What is the cardinality of this relationship?

 

ER Diagram Exercise: Draw a complete ER diagram for a HOSPITAL MANAGEMENT SYSTEM for a Nigerian Teaching Hospital. Include at minimum: PATIENT, DOCTOR, WARD, APPOINTMENT, PRESCRIPTION. For each entity, specify at least 4 attributes including the key attribute. Specify cardinality and participation for all relationships. You may use draw.io, Lucidchart, or pencil and paper.