ER diagram,
Entities are represented as rectangles and are connected to each other by lines, which represent the relationships between the entities. Each entity has a set of attributes, which are represented as ellipses connected to the entity rectangle.
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There are three types of relationships that can exist between entities in an ER diagram:
One-to-one (1:1) relationship:
This relationship exists when one entity is related to exactly one instance of another entity.
One-to-many (1:N) relationship:
This relationship exists when one entity is related to many instances of another entity.
Many-to-many (M:N) relationship:
This relationship exists when many instances of one entity are related to many instances of another entity.
ER diagrams are used to design and document database systems. They provide a visual representation of the data and relationships in the database, which can be helpful for understanding the structure of the database and for identifying any potential problems or issues.