DEFINITION OF ERD AND RELATED TERMS.

An ERD, or Entity-Relationship Diagram, is a graphical representation of entities, attributes, and relationships that are involved in a particular domain or system. ERDs are commonly used in database design to model the relationships between entities and their attributes.

Entities in an ERD refer to the objects or concepts that are being modelled. They are represented as rectangles with their name written inside. 

Attributes are characteristics or properties of the entities and are represented as ovals connected to their respective entity.

Cardinalities in an ERD describe the relationships between entities and indicate the number of occurrences of one entity that are associated with a single occurrence of the other entity. Cardinality is represented as a number or symbol on the relationship line between the two entities.

Several types of relationships can be represented in an ERD, including:

One-to-One (1:1) Relationship: This type of relationship occurs when each occurrence of one entity is associated with only one occurrence of the other entity.

One-to-Many (1:N) Relationship: This type of relationship occurs when each occurrence of one entity is associated with multiple occurrences of the other entity.

Many-to-One (N:1) Relationship: This type of relationship occurs when multiple occurrences of one entity are associated with only one occurrence of the other entity.

Many-to-Many (N:N) Relationship: This type of relationship occurs when multiple occurrences of one entity are associated with multiple occurrences of the other entity.

In an ERD, relationships are represented as lines connecting the entities, and cardinality is indicated using symbols or numbers on the line.

Overall, an ERD is a useful tool for visualizing the relationships between entities and their attributes and can help to guide the design and development of a database system.

REFERENCE

Entity Relationship Diagram (ERD) (2023) Available at: https://www.smartdraw.com/entity-relationship-diagram/#:~:text=An%20ERD%20visualizes%20the%20relationships,the%20logical%20structure%20of%20databases. (Accessed: 13 March 2023).