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.