WHAT IS ERD

 An ERD, or Entity-Relationship Diagram, is a visual representation of the relationships between entities in a database. It is a modeling tool used to design and understand the structure of a database. The ERD is composed of various symbols and notations, each of which has a specific meaning and use.

Entities are objects or concepts in a database that can be uniquely identified and represented in the ERD. They can represent anything from a physical object, such as a car, to an abstract concept, such as a customer. Each entity in the ERD is represented as a rectangle with its name inside.

Attributes are the characteristics or properties of an entity that describe its features. They are represented in the ERD as ovals connected to the corresponding entity. For example, the attributes of a car entity might include its make, model, and year.

Cardinalities are the relationships between entities, indicating the number of instances of one entity that are related to the number of instances of another entity. They are represented in the ERD as lines connecting the entities. There are three types of cardinalities: one-to-one (1:1), one-to-many (1:N), and many-to-many (N:N).

One-to-one cardinality indicates that one instance of an entity is related to only one instance of another entity. For example, one person can have only one driver's license.

One-to-many cardinality indicates that one instance of an entity is related to multiple instances of another entity. For example, one customer can have multiple orders.

Many-to-many cardinality indicates that multiple instances of an entity are related to multiple instances of another entity. For example, multiple students can be enrolled in multiple courses.

Relationships describe how entities are related to one another. They are represented in the ERD as diamonds connected to the corresponding entities. There are three types of relationships: one-to-one, one-to-many, and many-to-many.

In summary, an ERD is a modeling tool used to design and understand the structure of a database. It consists of entities, attributes, cardinalities, and relationships, each of which has a specific meaning and use. Entities represent objects or concepts in the database, attributes describe their characteristics, cardinalities indicate the relationships between entities, and relationships describe how entities are related to one another.

REFERENCE LIST

Entity Relationship Diagram (ERD). (n.d.). Techopedia. https://www.techopedia.com/definition/2186/entity-relationship-diagram-erd

Gupta, A. (2019). What is an Entity Relationship Diagram? (ERD). Guru99. https://www.guru99.com/entity-relationship-model.html

Cardinality. (n.d.). Oracle. https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/Cardinality.html