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Week 3

Site: Newgate University Minna - Elearning Platform
Course: Data Management
Book: Week 3
Printed by: Guest user
Date: Sunday, 14 June 2026, 3:53 AM

Description

Teaching and Learning Methods to be Employed

    i.         Illustrated lecture with step-by-step ER diagram construction

  ii.         Hands-on ER diagram drawing exercise (paper or draw.io)

iii.         Case study: Modelling a Nigerian hospital information system

 iv.         Collection of Assignment 1

Learning Outcomes / Objectives

By the end of this week, students should be able to:

1.    Explain the purpose of conceptual data modelling.

2.    Define entities, attributes, and relationships in the ER model.

3.    Classify attributes by type (simple, composite, multi-valued, derived).

4.    Identify and specify cardinality ratios and participation constraints.

5.    Draw a complete Entity-Relationship (ER) diagram for a given scenario.

Table of contents

3.1 Conceptual Data Modelling

Conceptual data modelling is the process of creating a high-level, abstract representation of the data requirements of an organisation, independent of any specific DBMS or physical implementation. The most widely used conceptual model is the Entity-Relationship (ER) model, introduced by Peter Chen in 1976.

The ER model allows database designers to communicate with non-technical stakeholders (managers, end users) using graphical diagrams that are easy to understand without database expertise.

Entities and Entity Sets

An ENTITY is a real-world object or concept that is distinguishable from other objects and about which data is to be stored.

EXAMPLES of entities in a Nigerian university database:

1.    STUDENT (each registered student is a distinct entity)

2.    COURSE (each taught course is an entity)

3.    LECTURER (each academic staff member is an entity)

4.    DEPARTMENT (each university department is an entity)

5.    EXAMINATION (each examination sitting is an entity)

An ENTITY TYPE is the category/classification. An ENTITY SET is the collection of all entities of a particular type. In ER diagrams, entity types are represented as RECTANGLES.

Strong vs. Weak Entities: A STRONG entity has its own unique identifier (primary key). E.g., STUDENT identified by MatricNumber. A WEAK entity cannot be uniquely identified by its own attributes alone and depends on a strong entity. E.g., a DEPENDENT (spouse/child) of a STAFF member identified only by (StaffID + DependentName). Weak entities are drawn as DOUBLE RECTANGLES.

3.2 Attributes

An ATTRIBUTE is a property or characteristic of an entity type. In ER diagrams, attributes are represented as OVALS connected to their entity type.

Attribute Type

Definition and Example

Simple (Atomic)

Cannot be divided further. E.g., StudentID, DateOfBirth, GPA

Composite

Can be divided into smaller sub-parts. E.g., Address → (StreetNo, StreetName, LGA, State). E.g., FullName → (FirstName, MiddleName, LastName)

Multi-valued

Can have multiple values for one entity. E.g., a Lecturer may have multiple PhoneNumbers. Drawn as DOUBLE OVAL.

Derived

Value is computed from other attributes. E.g., Age derived from DateOfBirth; TotalCreditUnits derived from registered courses. Drawn as DASHED OVAL.

Key Attribute

Uniquely identifies each entity instance. E.g., MatricNumber for STUDENT. Underlined in ER diagram.

Null Attribute

May have no value for some instances. E.g., MiddleName may be absent for some students.

3.3 Relationships and Cardinality Ratios

A RELATIONSHIP TYPE represents an association between two or more entity types. In ER diagrams, relationships are drawn as DIAMONDS connected to the participating entity types.

RELATIONSHIP EXAMPLES from Newgate University:

1.    STUDENT ENROLS-IN COURSE

2.    LECTURER TEACHES COURSE

3.    STUDENT BELONGS-TO DEPARTMENT

4.    STAFF HAS DEPENDENT

Cardinality Ratios

Cardinality describes the maximum number of times an entity instance in one entity type can be associated with instances of another entity type.

Cardinality

Notation

Nigerian Example

One-to-One (1:1)

1 — 1

One STAFF member has exactly one NIN (National Identity Number)

One-to-Many (1:N)

1 — N

One DEPARTMENT has many STUDENTS; each STUDENT belongs to one DEPARTMENT

Many-to-Many (M:N)

M — N

Many STUDENTS enrol in many COURSES; each COURSE has many STUDENTS

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.