An ER (Entity-Relationship) diagram is a type of diagram used to represent the data requirements and relationships of a system. In an ER diagram, entities are represented as rectangles and are connected to one another by lines, which represent relationships. Entities are typically things or concepts that are unique and can be identified by a set of attributes, which are represented by oval shapes connected to the entity rectangle by lines. Relationships between entities are represented by a diamond shape connected to the rectangles of the related entities.
ER diagrams are useful for modeling the data requirements of a system, and are often used in database design to visually represent the structure of a relational database. They can also be used to represent the relationships between data in other types of systems, such as file systems or data warehouses.
ER diagrams can also include cardinality and optionality symbols on the lines connecting the entities, which indicate the number of instances of an entity that can be associated with a single instance of another entity, and whether the relationship between the entities is required or optional.
